One document matched: draft-ietf-acme-acme-02.xml
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<rfc ipr="trust200902" docName="draft-ietf-acme-acme-02" category="std">
<front>
<title abbrev="ACME">Automatic Certificate Management Environment (ACME)</title>
<author initials="R." surname="Barnes" fullname="Richard Barnes">
<organization>Mozilla</organization>
<address>
<email>rlb@ipv.sx</email>
</address>
</author>
<author initials="J." surname="Hoffman-Andrews" fullname="Jacob Hoffman-Andrews">
<organization>EFF</organization>
<address>
<email>jsha@eff.org</email>
</address>
</author>
<author initials="J." surname="Kasten" fullname="James Kasten">
<organization>University of Michigan</organization>
<address>
<email>jdkasten@umich.edu</email>
</address>
</author>
<date year="2016" month="March" day="21"/>
<abstract>
<t>Certificates in the Web’s X.509 PKI (PKIX) are used for a number of purposes,
the most significant of which is the authentication of domain names. Thus,
certificate authorities in the Web PKI are trusted to verify that an applicant
for a certificate legitimately represents the domain name(s) in the certificate.
Today, this verification is done through a collection of ad hoc mechanisms.
This document describes a protocol that a certificate authority (CA) and an
applicant can use to automate the process of verification and certificate
issuance. The protocol also provides facilities for other certificate
management functions, such as certificate revocation.</t>
<t>DISCLAIMER: This is a work in progress draft of ACME and has not yet had a
thorough security analysis.</t>
<t>RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: The source for this draft is
maintained in GitHub. Suggested changes should be submitted as pull requests at
<eref target="https://github.com/ietf-wg-acme/acme">https://github.com/ietf-wg-acme/acme</eref>. Instructions are on that page as well.
Editorial changes can be managed in GitHub, but any substantive change should be
discussed on the ACME mailing list (acme@ietf.org).</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>Certificates in the Web PKI <xref target="RFC5280"/> are most commonly used to authenticate
domain names. Thus, certificate authorities in the Web PKI are trusted to
verify that an applicant for a certificate legitimately represents the domain
name(s) in the certificate.</t>
<t>Existing Web PKI certificate authorities tend to run on a set of ad hoc
protocols for certificate issuance and identity verification. A typical user
experience is something like:</t>
<t><list style="symbols">
<t>Generate a PKCS#10 <xref target="RFC2314"/> Certificate Signing Request (CSR).</t>
<t>Cut-and-paste the CSR into a CA web page.</t>
<t>Prove ownership of the domain by one of the following methods:
<list style="symbols">
<t>Put a CA-provided challenge at a specific place on the web server.</t>
<t>Put a CA-provided challenge at a DNS location corresponding to the target
domain.</t>
<t>Receive CA challenge at a (hopefully) administrator-controlled e-mail
address corresponding to the domain and then respond to it on the CA’s web
page.</t>
</list></t>
<t>Download the issued certificate and install it on their Web Server.</t>
</list></t>
<t>With the exception of the CSR itself and the certificates that are issued, these
are all completely ad hoc procedures and are accomplished by getting the human
user to follow interactive natural-language instructions from the CA rather than
by machine-implemented published protocols. In many cases, the instructions are
difficult to follow and cause significant confusion. Informal usability tests
by the authors indicate that webmasters often need 1-3 hours to obtain and
install a certificate for a domain. Even in the best case, the lack of
published, standardized mechanisms presents an obstacle to the wide deployment
of HTTPS and other PKIX-dependent systems because it inhibits mechanization of
tasks related to certificate issuance, deployment, and revocation.</t>
<t>This document describes an extensible framework for automating the issuance and
domain validation procedure, thereby allowing servers and infrastructural
software to obtain certificates without user interaction. Use of this protocol
should radically simplify the deployment of HTTPS and the practicality of PKIX
authentication for other protocols based on TLS <xref target="RFC5246"/>.</t>
</section>
<section anchor="deployment-model-and-operator-experience" title="Deployment Model and Operator Experience">
<t>The major guiding use case for ACME is obtaining certificates for Web sites
(HTTPS <xref target="RFC2818"/>). In that case, the server is intended to speak for one or
more domains, and the process of certificate issuance is intended to verify that
the server actually speaks for the domain(s).</t>
<t>Different types of certificates reflect different kinds of CA verification of
information about the certificate subject. “Domain Validation” (DV)
certificates are by far the most common type. For DV validation, the CA merely
verifies that the requester has effective control of the web server and/or DNS
server for the domain, but does not explicitly attempt to verify their
real-world identity. (This is as opposed to “Organization Validation” (OV) and
“Extended Validation” (EV) certificates, where the process is intended to also
verify the real-world identity of the requester.)</t>
<t>DV certificate validation commonly checks claims about properties related to
control of a domain name – properties that can be observed by the issuing
authority in an interactive process that can be conducted purely online. That
means that under typical circumstances, all steps in the request, verification,
and issuance process can be represented and performed by Internet protocols with
no out-of-band human intervention.</t>
<t>When deploying a current HTTPS server, an operator generally gets a prompt to
generate a self-signed certificate. When an operator deploys an ACME-compatible
web server, the experience would be something like this:</t>
<t><list style="symbols">
<t>The ACME client prompts the operator for the intended domain name(s) that the
web server is to stand for.</t>
<t>The ACME client presents the operator with a list of CAs from which it could
get a certificate. (This list will change over time based on the capabilities
of CAs and updates to ACME configuration.) The ACME client might prompt the
operator for payment information at this point.</t>
<t>The operator selects a CA.</t>
<t>In the background, the ACME client contacts the CA and requests that a
certificate be issued for the intended domain name(s).</t>
<t>Once the CA is satisfied, the certificate is issued and the ACME client
automatically downloads and installs it, potentially notifying the operator
via e-mail, SMS, etc.</t>
<t>The ACME client periodically contacts the CA to get updated certificates,
stapled OCSP responses, or whatever else would be required to keep the server
functional and its credentials up-to-date.</t>
</list></t>
<t>The overall idea is that it’s nearly as easy to deploy with a CA-issued
certificate as a self-signed certificate, and that once the operator has done
so, the process is self-sustaining with minimal manual intervention. Close
integration of ACME with HTTPS servers, for example, can allow the immediate and
automated deployment of certificates as they are issued, optionally sparing the
human administrator from additional configuration work.</t>
</section>
<section anchor="terminology" title="Terminology">
<t>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL
NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this
document are to be interpreted as described in RFC 2119 <xref target="RFC2119"/>.</t>
<t>The two main roles in ACME are “client” and “server”. The ACME client uses the
protocol to request certificate management actions, such as issuance or
revocation. An ACME client therefore typically runs on a web server, mail
server, or some other server system which requires valid TLS certificates. The
ACME server runs at a certificate authority, and responds to client requests,
performing the requested actions if the client is authorized.</t>
<t>An ACME client is represented by an “account key pair”. The client uses the
private key of this key pair to sign all messages sent to the server. The
server uses the public key to verify the authenticity and integrity of messages
from the client.</t>
</section>
<section anchor="protocol-overview" title="Protocol Overview">
<t>ACME allows a client to request certificate management actions using a set of
JSON messages carried over HTTPS. In some ways, ACME functions much like a
traditional CA, in which a user creates an account, adds identifiers to that
account (proving control of the domains), and requests certificate issuance for
those domains while logged in to the account.</t>
<t>In ACME, the account is represented by an account key pair. The “add a domain”
function is accomplished by authorizing the key pair for a given domain.
Certificate issuance and revocation are authorized by a signature with the key
pair.</t>
<t>The first phase of ACME is for the client to register with the ACME server. The
client generates an asymmetric key pair and associates this key pair with a set
of contact information by signing the contact information. The server
acknowledges the registration by replying with a registration object echoing the
client’s input.</t>
<figure><artwork><![CDATA[
Client Server
Contact Information
Signature ------->
<------- Registration
]]></artwork></figure>
<t>Before a client can issue certificates, it must establish an authorization with
the server for an account key pair to act for the identifier(s) that it wishes
to include in the certificate. To do this, the client must demonstrate to the
server both (1) that it holds the private key of the account key pair, and (2)
that it has authority over the identifier being claimed.</t>
<t>Proof of possession of the account key is built into the ACME protocol. All
messages from the client to the server are signed by the client, and the server
verifies them using the public key of the account key pair.</t>
<t>To verify that the client controls the identifier being claimed, the server
issues the client a set of challenges. Because there are many different ways to
validate possession of different types of identifiers, the server will choose
from an extensible set of challenges that are appropriate for the identifier
being claimed. The client responds with a set of responses that tell the server
which challenges the client has completed. The server then validates the
challenges to check that the client has accomplished the challenge.</t>
<t>For example, if the client requests a domain name, the server might challenge
the client to provision a record in the DNS under that name, or to provision a
file on a web server referenced by an A or AAAA record under that name. The
server would then query the DNS for the record in question, or send an HTTP
request for the file. If the client provisioned the DNS or the web server as
expected, then the server considers the client authorized for the domain name.</t>
<figure><artwork><![CDATA[
Client Server
Identifier
Signature ------->
<------- Challenges
Responses
Signature ------->
<------- Updated Challenge
<~~~~~~~~Validation~~~~~~~~>
Poll ------->
<------- Authorization
]]></artwork></figure>
<t>Once the client has authorized an account key pair for an identifier, it can use
the key pair to authorize the issuance of certificates for the identifier. To
do this, the client sends a PKCS#10 Certificate Signing Request (CSR) to the
server (indicating the identifier(s) to be included in the issued certificate)
and a signature over the CSR by the private key of the account key pair.</t>
<t>Note that as a result, the CSR is signed twice: One by the private key
corresponding to the public key in the CSR, and once by the private key of the
account key pair. The former signature indicates that the holder of the key in
the CSR is willing to act for the indicated identifiers, and the latter
signature indicates to the server that the issuance of the certificate is
authorized by the client (i.e., the domain holder).</t>
<t>If the server agrees to issue the certificate, then it creates the certificate
and provides it in its response. The certificate is assigned a URI, which the
client can use to fetch updated versions of the certificate.</t>
<figure><artwork><![CDATA[
Client Server
CSR
Signature -------->
<-------- Certificate
]]></artwork></figure>
<t>To revoke a certificate, the client simply sends a revocation request indicating
the certificate to be revoked, signed with an authorized key pair. The server
indicates whether the request has succeeded.</t>
<figure><artwork><![CDATA[
Client Server
Revocation request
Signature -------->
<-------- Result
]]></artwork></figure>
<t>Note that while ACME is defined with enough flexibility to handle different
types of identifiers in principle, the primary use case addressed by this
document is the case where domain names are used as identifiers. For example,
all of the identifier validation challenges described in
<xref target="identifier-validation-challenges"/> below address validation of domain names.
The use of ACME for other protocols will require further specification, in order
to describe how these identifiers are encoded in the protocol, and what types of
validation challenges the server might require.</t>
</section>
<section anchor="message-transport" title="Message Transport">
<t>ACME uses a combination of HTTPS and JWS to create a messaging layer with a few
important security properties.</t>
<t>Communications between an ACME client and an ACME server are done over HTTPS,
using JWS to provide som additional security properties for messages sent from
the client to the server. HTTPS provides server authentication and
confidentiality. With some ACME-specific extensions, JWS provides
authentication of the client’s request payloads, anti-replay protection, and a
degree of integrity for the HTTPS request URI.</t>
<section anchor="https-requests" title="HTTPS Requests">
<t>Each ACME function is accomplished by the client sending a sequence of HTTPS
requests to the server, carrying JSON messages <xref target="RFC2818"/><xref target="RFC7159"/>. Use of
HTTPS is REQUIRED. Clients SHOULD support HTTP public key pinning <xref target="RFC7469"/>,
and servers SHOULD emit pinning headers. Each subsection of
<xref target="certificate-management"/> below describes the message formats used by the
function, and the order in which messages are sent.</t>
<t>In all HTTPS transactions used by ACME, the ACME client is the HTTPS client and
the ACME server is the HTTPS server.</t>
<t>ACME servers that are intended to be generally accessible need to use
Cross-Origin Resource Sharing (CORS) in order to be accessible from
browser-based clients <xref target="W3C.CR-cors-20130129"/>. Such servers SHOULD set the
Access-Control-Allow-Origin header field to the value “*”.</t>
<t>Binary fields in the JSON objects used by ACME are encoded using base64url
encoding described in <xref target="RFC4648"/> Section 5, according to the profile specified
in JSON Web Signature <xref target="RFC7515"/> Section 2. This encoding uses a URL safe
character set. Trailing ‘=’ characters MUST be stripped.</t>
</section>
<section anchor="request-authentication" title="Request Authentication">
<t>All ACME requests with a non-empty body MUST encapsulate the body in a JWS
object, signed using the account key pair. The server MUST verify the JWS
before processing the request. (For readability, however, the examples below
omit this encapsulation.) Encapsulating request bodies in JWS provides a simple
authentication of requests by way of key continuity.</t>
<t>JWS objects sent in ACME requests MUST meet the following additional criteria:</t>
<t><list style="symbols">
<t>The JWS MUST use the Flattened JSON Serialization</t>
<t>The JWS MUST be encoded using UTF-8</t>
<t>The JWS Header or Protected Header MUST include “alg” and “jwk” fields</t>
<t>The JWS MUST NOT have the value “none” in its “alg” field</t>
<t>The JWS Protected Header MUST include the “nonce” field (defined below)</t>
</list></t>
<t>Note that this implies that GET requests are not authenticated. Servers MUST
NOT respond to GET requests for resources that might be considered sensitive.</t>
</section>
<section anchor="request-uri-type-integrity" title="Request URI Type Integrity">
<t>It is common in deployment the entity terminating TLS for HTTPS to be different
from the entity operating the logical HTTPS server, with a “request routing”
layer in the middle. For example, an ACME CA might have a content delivery
network terminate TLS connections from clients so that it can inspect client
requests for denial-of-service protection.</t>
<t>These intermediaries can also change values in the request that are not signed
in the HTTPS request, e.g., the request URI and headers. ACME uses JWS to
provides a limited integrity mechanism, which protects against an intermediary
changing the request URI to anothe ACME URI of a different type. (It does not
protect against changing between URIs of the same type, e.g., from one
authorization URI to another).</t>
<t>An ACME request carries a JSON dictionary that provides the details of the
client’s request to the server. Each request object MUST have a “resource”
field that indicates what type of resource the request is addressed to, as
defined in the below table:</t>
<texttable>
<ttcol align='left'>Resource type</ttcol>
<ttcol align='left'>“resource” value</ttcol>
<c>New registration</c>
<c>new-reg</c>
<c>New authorization</c>
<c>new-authz</c>
<c>New certificate</c>
<c>new-cert</c>
<c>Revoke certificate</c>
<c>revoke-cert</c>
<c>Registration</c>
<c>reg</c>
<c>Authorization</c>
<c>authz</c>
<c>Challenge</c>
<c>challenge</c>
<c>Certificate</c>
<c>cert</c>
</texttable>
<t>Other fields in ACME request bodies are described below.</t>
</section>
<section anchor="replay-protection" title="Replay protection">
<t>In order to protect ACME resources from any possible replay attacks, ACME
requests have a mandatory anti-replay mechanism. This mechanism is based on the
server maintaining a list of nonces that it has issued to clients, and requiring
any signed request from the client to carry such a nonce.</t>
<t>An ACME server MUST include a Replay-Nonce header field in each successful
response it provides to a client, with contents as specified below. In
particular, the ACME server MUST provide a Replay-Nonce header field in response
to a HEAD request for any valid resource. (This allows clients to easily obtain
a fresh nonce.) It MAY also provide nonces in error responses.</t>
<t>Every JWS sent by an ACME client MUST include, in its protected header, the
“nonce” header parameter, with contents as defined below. As part of JWS
verification, the ACME server MUST verify that the value of the “nonce” header
is a value that the server previously provided in a Replay-Nonce header field.
Once a nonce value has appeared in an ACME request, the server MUST consider it
invalid, in the same way as a value it had never issued.</t>
<t>When a server rejects a request because its nonce value was unacceptable (or not
present), it SHOULD provide HTTP status code 400 (Bad Request), and indicate the
ACME error code “urn:ietf:params:acme:error:badNonce”.</t>
<t>The precise method used to generate and track nonces is up to the server. For
example, the server could generate a random 128-bit value for each response,
keep a list of issued nonces, and strike nonces from this list as they are used.</t>
<section anchor="replay-nonce" title="Replay-Nonce">
<t>The “Replay-Nonce” header field includes a server-generated value that the
server can use to detect unauthorized replay in future client requests. The
server should generate the value provided in Replay-Nonce in such a way that
they are unique to each message, with high probability.</t>
<t>The value of the Replay-Nonce field MUST be an octet string encoded according to
the base64url encoding described in Section 2 of <xref target="RFC7515"/>. Clients MUST
ignore invalid Replay-Nonce values.</t>
<figure><artwork><![CDATA[
base64url = [A-Z] / [a-z] / [0-9] / "-" / "_"
Replay-Nonce = *base64url
]]></artwork></figure>
<t>The Replay-Nonce header field SHOULD NOT be included in HTTP request messages.</t>
</section>
<section anchor="nonce-nonce-jws-header-parameter" title="“nonce” (Nonce) JWS header parameter">
<t>The “nonce” header parameter provides a unique value that enables the verifier
of a JWS to recognize when replay has occurred. The “nonce” header parameter
MUST be carried in the protected header of the JWS.</t>
<t>The value of the “nonce” header parameter MUST be an octet string, encoded
according to the base64url encoding described in Section 2 of <xref target="RFC7515"/>. If
the value of a “nonce” header parameter is not valid according to this encoding,
then the verifier MUST reject the JWS as malformed.</t>
</section>
</section>
<section anchor="errors" title="Errors">
<t>Errors can be reported in ACME both at the HTTP layer and within ACME payloads.
ACME servers can return responses with an HTTP error response code (4XX or 5XX).
For example: If the client submits a request using a method not allowed in this
document, then the server MAY return status code 405 (Method Not Allowed).</t>
<t>When the server responds with an error status, it SHOULD provide additional
information using problem document <xref target="I-D.ietf-appsawg-http-problem"/>.
To facilitate automatic response
to errors, this document defines the following standard tokens for use in the
“type” field (within the “urn:ietf:params:acme:error:” namespace):</t>
<texttable>
<ttcol align='left'>Code</ttcol>
<ttcol align='left'>Description</ttcol>
<c>badCSR</c>
<c>The CSR is unacceptable (e.g., due to a short key)</c>
<c>badNonce</c>
<c>The client sent an unacceptable anti-replay nonce</c>
<c>connection</c>
<c>The server could not connect to the client for validation</c>
<c>dnssec</c>
<c>The server could not validate a DNSSEC signed domain</c>
<c>malformed</c>
<c>The request message was malformed</c>
<c>serverInternal</c>
<c>The server experienced an internal error</c>
<c>tls</c>
<c>The server experienced a TLS error during validation</c>
<c>unauthorized</c>
<c>The client lacks sufficient authorization</c>
<c>unknownHost</c>
<c>The server could not resolve a domain name</c>
<c>rateLimited</c>
<c>The request exceeds a rate limit</c>
<c>invalidContact</c>
<c>The provided contact URI for a registration was invalid</c>
</texttable>
<t>This list is not exhaustive. The server MAY return errors whose “type” field is
set to a URI other than those defined above. Servers MUST NOT use the ACME URN
namespace for errors other than the standard types. Clients SHOULD display the
“detail” field of such errors.</t>
<t>Authorization and challenge objects can also contain error information to
indicate why the server was unable to validate authorization.</t>
</section>
</section>
<section anchor="certificate-management" title="Certificate Management">
<t>In this section, we describe the certificate management functions that ACME
enables:</t>
<t><list style="symbols">
<t>Account Key Registration</t>
<t>Account Key Authorization</t>
<t>Certificate Issuance</t>
<t>Certificate Renewal</t>
<t>Certificate Revocation</t>
</list></t>
<section anchor="resources" title="Resources">
<t>ACME is structured as a REST application with a few types of resources:</t>
<t><list style="symbols">
<t>Registration resources, representing information about an account</t>
<t>Authorization resources, representing an account’s authorization to act for an
identifier</t>
<t>Challenge resources, representing a challenge to prove control of an
identifier</t>
<t>Certificate resources, representing issued certificates</t>
<t>A “directory” resource</t>
<t>A “new-registration” resource</t>
<t>A “new-authorization” resource</t>
<t>A “new-certificate” resource</t>
<t>A “revoke-certificate” resource</t>
</list></t>
<t>For the “new-X” resources above, the server MUST have exactly one resource for
each function. This resource may be addressed by multiple URIs, but all must
provide equivalent functionality.</t>
<t>ACME uses different URIs for different management functions. Each function is
listed in a directory along with its corresponding URI, so clients only need to
be configured with the directory URI. These URIs are connected by a few
different link relations <xref target="RFC5988"/>.</t>
<t>The “up” link relation is used with challenge resources to indicate the
authorization resource to which a challenge belongs. It is also used from
certificate resources to indicate a resource from which the client may fetch a
chain of CA certificates that could be used to validate the certificate in the
original resource.</t>
<t>The “directory” link relation is present on all resources other than the
directory and indicates the directory URL.</t>
<t>The following diagram illustrates the relations between resources on an ACME
server. The solid lines indicate link relations, and the dotted lines
correspond to relationships expressed in other ways, e.g., the Location header
in a 201 (Created) response.</t>
<figure><artwork><![CDATA[
directory
.
.
....................................................
. . . .
. . . .
V "next" V "next" V V
new-reg ---+----> new-authz ---+----> new-cert revoke-cert
. | . | . ^
. | . | . | "revoke"
V | V | V |
reg* ----+ authz -----+ cert-----------+
. ^ |
. | "up" | "up"
V | V
challenge cert-chain
]]></artwork></figure>
<t>The following table illustrates a typical sequence of requests required to
establish a new account with the server, prove control of an identifier, issue a
certificate, and fetch an updated certificate some time after issuance. The
“->” is a mnemonic for a Location header pointing to a created resource.</t>
<texttable>
<ttcol align='left'>Action</ttcol>
<ttcol align='left'>Request</ttcol>
<ttcol align='left'>Response</ttcol>
<c>Register</c>
<c>POST new-reg</c>
<c>201 -> reg</c>
<c>Request challenges</c>
<c>POST new-authz</c>
<c>201 -> authz</c>
<c>Answer challenges</c>
<c>POST challenge</c>
<c>200</c>
<c>Poll for status</c>
<c>GET authz</c>
<c>200</c>
<c>Request issuance</c>
<c>POST new-cert</c>
<c>201 -> cert</c>
<c>Check for new cert</c>
<c>GET cert</c>
<c>200</c>
</texttable>
<t>The remainder of this section provides the details of how these resources are
structured and how the ACME protocol makes use of them.</t>
<section anchor="registration-objects" title="Registration Objects">
<t>An ACME registration resource represents a set of metadata associated to an
account key pair. Registration resources have the following structure:</t>
<t><list style="hanging">
<t hangText='key (required, dictionary):'>
The public key of the account key pair, encoded as a JSON Web Key object
<xref target="RFC7517"/>.</t>
<t hangText='contact (optional, array of string):'>
An array of URIs that the server can use to contact the client for issues
related to this authorization. For example, the server may wish to notify the
client about server-initiated revocation.</t>
<t hangText='agreement (optional, string):'>
A URI referring to a subscriber agreement or terms of service provided by the
server (see below). Including this field indicates the client’s agreement with
the referenced terms.</t>
<t hangText='authorizations (required, string):'>
A URI from which a list of authorizations granted to this account can be
fetched via a GET request. The result of the GET request MUST be a JSON object
whose “authorizations” field is an array of strings, where each string is the
URI of an authorization belonging to this registration. The server SHOULD
include pending authorizations, and SHOULD NOT include authorizations that are
invalid or expired. The server MAY return an incomplete list, along with a Link
header with link relation “next” indicating a URL to retrieve further entries.</t>
<t hangText='certificates (required, string):'>
A URI from which a list of certificates issued for this account can be fetched
via a GET request. The result of the GET request MUST be a JSON object whose
“certificates” field is an array of strings, where each string is the URI of a
certificate. The server SHOULD NOT include expired or revoked certificates.
The server MAY return an incomplete list, along with a Link header with link
relation “next” indicating a URL to retrieve further entries.</t>
</list></t>
<figure><artwork><![CDATA[
{
"resource": "new-reg",
"contact": [
"mailto:cert-admin@example.com",
"tel:+12025551212"
],
"agreement": "https://example.com/acme/terms",
"authorizations": "https://example.com/acme/reg/1/authz",
"certificates": "https://example.com/acme/reg/1/cert",
}
]]></artwork></figure>
</section>
<section anchor="authorization-objects" title="Authorization Objects">
<t>An ACME authorization object represents server’s authorization for an account to
represent an identifier. In addition to the identifier, an authorization
includes several metadata fields, such as the status of the authorization (e.g.,
“pending”, “valid”, or “revoked”) and which challenges were used to validate
possession of the identifier.</t>
<t>The structure of an ACME authorization resource is as follows:</t>
<t><list style="hanging">
<t hangText='identifier (required, dictionary of string):'>
The identifier that the account is authorized to represent
<list style="hanging">
<t hangText='type (required, string):'>
The type of identifier.</t>
<t hangText='value (required, string):'>
The identifier itself.</t>
</list>
</t>
<t hangText='status (required, string):'>
The status of this authorization. Possible values are: “unknown”, “pending”,
“processing”, “valid”, “invalid” and “revoked”. If this field is missing, then
the default value is “pending”.</t>
<t hangText='expires (optional, string):'>
The timestamp after which the server will consider this authorization invalid,
encoded in the format specified in RFC 3339 <xref target="RFC3339"/>. This field is REQUIRED
for objects with “valid” in the “status field.</t>
<t hangText='challenges (required, array):'>
The challenges that the client needs to fulfill
in order to prove possession of the identifier (for pending authorizations).
For final authorizations, the challenges that were used. Each array entry is a
dictionary with parameters required to validate the challenge, as specified in
<xref target="identifier-validation-challenges"/>.</t>
<t hangText='combinations (optional, array of arrays of integers):'>
A collection of sets of
challenges, each of which would be sufficient to prove possession of the
identifier. Clients complete a set of challenges that covers at least one
set in this array. Challenges are identified by their indices in the challenges
array. If no “combinations” element is included in an authorization object, the
client completes all challenges.</t>
</list></t>
<t>The only type of identifier defined by this specification is a fully-qualified
domain name (type: “dns”). The value of the identifier MUST be the ASCII
representation of the domain name. Wildcard domain names (with “*” as the first
label) MUST NOT be included in authorization requests. See
<xref target="certificate-issuance"/> below for more information about wildcard domains.</t>
<figure><artwork><![CDATA[
{
"status": "valid",
"expires": "2015-03-01T14:09:00Z",
"identifier": {
"type": "dns",
"value": "example.org"
},
"challenges": [
{
"type": "http-01",
"status": "valid",
"validated": "2014-12-01T12:05:00Z",
"keyAuthorization": "SXQe-2XODaDxNR...vb29HhjjLPSggwiE"
}
],
}
]]></artwork></figure>
</section>
</section>
<section anchor="directory" title="Directory">
<t>In order to help clients configure themselves with the right URIs for each ACME
operation, ACME servers provide a directory object. This should be the only URL
needed to configure clients. It is a JSON dictionary, whose keys are the
“resource” values listed in <xref target="https-requests"/>, and whose values are the
URIs used to accomplish the corresponding function.</t>
<t>There is no constraint on the actual URI of the directory except that it
should be different from the other ACME server resources’ URIs, and that it
should not clash with other services. For instance:</t>
<t><list style="symbols">
<t>a host which function as both an ACME and Web server may want to keep
the root path “/” for an HTML “front page”, and and place the ACME
directory under path “/acme”.</t>
<t>a host which only functions as an ACME server could place the directory
under path “/”.</t>
</list></t>
<t>The dictionary MAY additionally contain a key “meta”. If present, it MUST be a
JSON dictionary; each item in the dictionary is an item of metadata relating to
the service provided by the ACME server.</t>
<t>The following metadata items are defined, all of which are OPTIONAL:</t>
<t><list style="hanging">
<t hangText='“terms-of-service” (optional, string):'>
A URI identifying the current terms of service.</t>
<t hangText='“website” (optional, string)):'>
An HTTP or HTTPS URL locating a website providing more
information about the ACME server.</t>
<t hangText='“caa-identities” (optional, array of string):'>
Each string MUST be a lowercase hostname which the ACME server recognises as
referring to itself for the purposes of CAA record validation as defined in
<xref target="RFC6844"/>. This allows clients to determine the correct issuer domain name to
use when configuring CAA record.</t>
</list></t>
<t>Clients access the directory by sending a GET request to the directory URI.</t>
<figure><artwork><![CDATA[
HTTP/1.1 200 OK
Content-Type: application/json
{
"new-reg": "https://example.com/acme/new-reg",
"new-authz": "https://example.com/acme/new-authz",
"new-cert": "https://example.com/acme/new-cert",
"revoke-cert": "https://example.com/acme/revoke-cert",
"meta": {
"terms-of-service": "https://example.com/acme/terms",
"website": "https://www.example.com/",
"caa-identities": ["example.com"]
}
}
]]></artwork></figure>
</section>
<section anchor="registration" title="Registration">
<t>A client creates a new account with the server by sending a POST request to the
server’s new-registration URI. The body of the request is a stub registration
object containing only the “contact” field (along with the required “resource”
field).</t>
<figure><artwork><![CDATA[
POST /acme/new-registration HTTP/1.1
Host: example.com
{
"resource": "new-reg",
"contact": [
"mailto:cert-admin@example.com",
"tel:+12025551212"
],
}
/* Signed as JWS */
]]></artwork></figure>
<t>The server MUST ignore any values provided in the “key”, “authorizations”, and
“certificates” fields in registration bodies sent by the client, as well as any
other fields that it does not recognize. If new fields are specified in the
future, the specification of those fields MUST describe whether they may be
provided by the client.</t>
<t>The server creates a registration object with the included contact information.
The “key” element of the registration is set to the public key used to verify
the JWS (i.e., the “jwk” element of the JWS header). The server returns this
registration object in a 201 (Created) response, with the registration URI in a
Location header field. The server SHOULD also indicate its new-authorization
URI using the “next” link relation.</t>
<t>If the server already has a registration object with the provided account key,
then it MUST return a 409 (Conflict) response and provide the URI of that
registration in a Location header field. This allows a client that has an
account key but not the corresponding registration URI to recover the
registration URI.</t>
<t>If the server wishes to present the client with terms under which the ACME
service is to be used, it MUST indicate the URI where such terms can be accessed
in a Link header with link relation “terms-of-service”. As noted above, the
client may indicate its agreement with these terms by updating its registration
to include the “agreement” field, with the terms URI as its value. When these
terms change in a way that requires an agreement update, the server MUST
use a different URI in the Link header.</t>
<figure><artwork><![CDATA[
HTTP/1.1 201 Created
Content-Type: application/json
Location: https://example.com/acme/reg/asdf
Link: <https://example.com/acme/new-authz>;rel="next"
Link: <https://example.com/acme/terms>;rel="terms-of-service"
Link: <https://example.com/acme/some-directory>;rel="directory"
{
"key": { /* JWK from JWS header */ },
"contact": [
"mailto:cert-admin@example.com",
"tel:+12025551212"
]
}
]]></artwork></figure>
<t>If the client wishes to update this information in the future, it sends a POST
request with updated information to the registration URI. The server MUST
ignore any updates to the “key”, “authorizations, or “certificates” fields, and
MUST verify that the request is signed with the private key corresponding to the
“key” field of the request before updating the registration.</t>
<t>For example, to update the contact information in the above registration, the
client could send the following request:</t>
<figure><artwork><![CDATA[
POST /acme/reg/asdf HTTP/1.1
Host: example.com
{
"resource": "reg",
"contact": [
"mailto:certificates@example.com",
"tel:+12125551212"
],
}
/* Signed as JWS */
]]></artwork></figure>
<t>Servers SHOULD NOT respond to GET requests for registration resources as these
requests are not authenticated. If a client wishes to query the server for
information about its account (e.g., to examine the “contact” or “certificates”
fields), then it SHOULD do so by sending a POST request with an empty update.
That is, it should send a JWS whose payload is trivial ({“resource”:”reg”}).
In this case the server reply MUST contain the same link headers sent for a
new registration, to allow a client to retrieve the “new-authorization” and
“terms-of-service” URI</t>
<section anchor="account-key-roll-over" title="Account Key Roll-over">
<t>A client may wish to change the public key that is associated with a
registration, e.g., in order to mitigate the risk of key compromise. To do
this, the client first constructs a JSON object representing a request to
update the registration:</t>
<t><list style="hanging">
<t hangText='resource (required, string):'>
The string “reg”, indicating an update to the registration.</t>
<t hangText='oldKey (required, string):'>
The JWK thumbprint of the old key <xref target="RFC7638"/>, base64url-encoded</t>
</list></t>
<figure><artwork><![CDATA[
{
"resource": "reg",
"oldKey": "D7J9RL1f-RWUl68JP-gW1KSl2TkIrJB7hK6rLFFeYMU"
}
]]></artwork></figure>
<t>The client signs this object with the new key pair and encodes the object and
signature as a JWS. The client then sends this JWS to the server in the
“newKey” field of a request to update the registration.</t>
<figure><artwork><![CDATA[
POST /acme/reg/asdf HTTP/1.1
Host: example.com
{
"resource": "reg",
"newKey": /* JSON object signed as JWS with new key */
}
/* Signed as JWS with original key */
]]></artwork></figure>
<t>On receiving a request to the registration URL with the “newKey” attribute set,
the server MUST perform the following steps:</t>
<t><list style="numbers">
<t>Check that the contents of the “newKey” attribute are a valid JWS</t>
<t>Check that the “newKey” JWS verifies using the key in the “jwk” header
parameter of the JWS</t>
<t>Check that the payload of the JWS is a valid JSON object</t>
<t>Check that the “resource” field of the object has the value “reg”</t>
<t>Check that the “oldKey” field of the object contains the JWK thumbprint of
the account key for this registration</t>
</list></t>
<t>If all of these checks pass, then the server updates the registration by
replacing the old account key with the public key carried in the “jwk” header
parameter of the “newKey” JWS object.</t>
<t>If the update was successful, then the server sends a response with status code
200 (OK) and the updated registration object as its body. If the update was not
successful, then the server responds with an error status code and a problem
document describing the error.</t>
</section>
<section anchor="deleting-an-account" title="Deleting an Account">
<t>If a client no longer wishes to have an account key registered with the server,
it may request that the server delete its account by sending a POST request to
the account URI containing the “delete” field.</t>
<t>delete (required, boolean):
The boolean value “true”.</t>
<t>The request object MUST contain the “resource” field as required above (with the
value “reg”). It MUST NOT contain any fields besides “resource” and “delete”.</t>
<t>Note that although this object is very simple, the risk of replay or fraudulent
generation via signing oracles is mitigated by the need for an anti-replay
token in the protected header of the JWS.</t>
<figure><artwork><![CDATA[
POST /acme/reg/asdf HTTP/1.1
Host: example.com
{
"resource": "reg",
"delete": true,
}
/* Signed as JWS */
]]></artwork></figure>
<t>On receiving a POST to an account URI containing a “delete” field, the server
MUST verify that no other fields were sent in the object (other than
“resource”), and it MUST verify that the value of the “delete” field is “true”
(as a boolean, not a string). If either of these checks fails, then the server
MUST reject the request with status code 400 (Bad Request).</t>
<t>If the server accepts the deletion request, then it MUST delete the account and
all related objects and send a response with a 200 (OK) status code and an empty
body. The server SHOULD delete any authorization objects related to the deleted
account, since they can no longer be used. The server SHOULD NOT delete
certificate objects related to the account, since certificates issued under the
account continue to be valid until they expire or are revoked.</t>
</section>
</section>
<section anchor="identifier-authorization" title="Identifier Authorization">
<t>The identifier authorization process establishes the authorization of an account
to manage certificates for a given identifier. This process must assure the
server of two things: First, that the client controls the private key of the
account key pair, and second, that the client holds the identifier in question.
This process may be repeated to associate multiple identifiers to a key pair
(e.g., to request certificates with multiple identifiers), or to associate
multiple accounts with an identifier (e.g., to allow multiple entities to
manage certificates).</t>
<t>As illustrated by the figure in the overview section above, the authorization
process proceeds in two phases. The client first requests a new authorization,
and the server issues challenges, then the client responds to those challenges
and the server validates the client’s responses.</t>
<t>To begin the key authorization process, the client sends a POST request to the
server’s new-authorization resource. The body of the POST request MUST contain
a JWS object, whose payload is a partial authorization object. This JWS object
MUST contain only the “identifier” field, so that the server knows what
identifier is being authorized. The server MUST ignore any other fields present
in the client’s request object.</t>
<t>The authorization object is implicitly tied to the account key used to sign the
request. Once created, the authorization may only be updated by that account.</t>
<figure><artwork><![CDATA[
POST /acme/new-authorization HTTP/1.1
Host: example.com
{
"resource": "new-authz",
"identifier": {
"type": "dns",
"value": "example.org"
}
}
/* Signed as JWS */
]]></artwork></figure>
<t>Before processing the authorization further, the server SHOULD determine whether
it is willing to issue certificates for the identifier. For example, the server
should check that the identifier is of a supported type. Servers might also
check names against a blacklist of known high-value identifiers. If the server
is unwilling to issue for the identifier, it SHOULD return a 403 (Forbidden)
error, with a problem document describing the reason for the rejection.</t>
<t>If the server is willing to proceed, it builds a pending authorization object
from the initial authorization object submitted by the client.</t>
<t><list style="symbols">
<t>“identifier” the identifier submitted by the client</t>
<t>“status”: MUST be “pending” unless the server has out-of-band information
about the client’s authorization status</t>
<t>“challenges” and “combinations”: As selected by the server’s policy for this
identifier</t>
</list></t>
<t>The server allocates a new URI for this authorization, and returns a 201
(Created) response, with the authorization URI in a Location header field, and
the JSON authorization object in the body.</t>
<figure><artwork><![CDATA[
HTTP/1.1 201 Created
Content-Type: application/json
Location: https://example.com/authz/asdf
Link: <https://example.com/acme/new-cert>;rel="next"
Link: <https://example.com/acme/some-directory>;rel="directory"
{
"status": "pending",
"identifier": {
"type": "dns",
"value": "example.org"
},
"challenges": [
{
"type": "http-01",
"uri": "https://example.com/authz/asdf/0",
"token": "IlirfxKKXAsHtmzK29Pj8A"
},
{
"type": "dns-01",
"uri": "https://example.com/authz/asdf/1",
"token": "DGyRejmCefe7v4NfDGDKfA"
}
},
"combinations": [[0], [1]]
}
]]></artwork></figure>
<section anchor="responding-to-challenges" title="Responding to Challenges">
<t>To prove control of the identifer and receive authorization, the client needs to
respond with information to complete the challenges. To do this, the client
updates the authorization object received from the server by filling in any
required information in the elements of the “challenges” dictionary. (This is
also the stage where the client should perform any actions required by the
challenge.)</t>
<t>The client sends these updates back to the server in the form of a JSON object
with the response fields required by the challenge type, carried in a POST
request to the challenge URI (not authorization URI or the new-authorization
URI). This allows the client to send information only for challenges it is
responding to.</t>
<t>For example, if the client were to respond to the “http-01” challenge in the
above authorization, it would send the following request:</t>
<figure><artwork><![CDATA[
POST /acme/authz/asdf/0 HTTP/1.1
Host: example.com
{
"resource": "challenge",
"type": "http-01",
"keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggwiE"
}
/* Signed as JWS */
]]></artwork></figure>
<t>The server updates the authorization document by updating its representation of
the challenge with the response fields provided by the client. The server MUST
ignore any fields in the response object that are not specified as response
fields for this type of challenge. The server provides a 200 (OK) response
with the updated challenge object as its body.</t>
<t>If the client’s response is invalid for some reason, or does not provide the
server with appropriate information to validate the challenge, then the server
MUST return an HTTP error. On receiving such an error, the client SHOULD undo
any actions that have been taken to fulfill the challenge, e.g., removing files
that have been provisioned to a web server.</t>
<t>Presumably, the client’s responses provide the server with enough information to
validate one or more challenges. The server is said to “finalize” the
authorization when it has completed all the validations it is going to complete,
and assigns the authorization a status of “valid” or “invalid”, corresponding to
whether it considers the account authorized for the identifier. If the final
state is “valid”, the server MUST add an “expires” field to the authorization.
When finalizing an authorization, the server MAY remove the “combinations” field
(if present) or remove any challenges still pending. The server SHOULD NOT
remove challenges with status “invalid”.</t>
<t>Usually, the validation process will take some time, so the client will need to
poll the authorization resource to see when it is finalized. For challenges
where the client can tell when the server has validated the challenge (e.g., by
seeing an HTTP or DNS request from the server), the client SHOULD NOT begin
polling until it has seen the validation request from the server.</t>
<t>To check on the status of an authorization, the client sends a GET request to
the authorization URI, and the server responds with the current authorization
object. In responding to poll requests while the validation is still in
progress, the server MUST return a 202 (Accepted) response, and MAY include a
Retry-After header field to suggest a polling interval to the client.</t>
<figure><artwork><![CDATA[
GET /acme/authz/asdf HTTP/1.1
Host: example.com
HTTP/1.1 200 OK
{
"status": "valid",
"expires": "2015-03-01T14:09:00Z",
"identifier": {
"type": "dns",
"value": "example.org"
},
"challenges": [
{
"type": "http-01"
"status": "valid",
"validated": "2014-12-01T12:05:00Z",
"token": "IlirfxKKXAsHtmzK29Pj8A",
"keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggwiE"
}
]
}
]]></artwork></figure>
</section>
<section anchor="deleting-an-authorization" title="Deleting an Authorization">
<t>If a client wishes to relinquish its authorization to issue certificates for an
identifier, then it may request that the server delete the authorization. The
client makes this request by sending a POST request to the authorization URI
containing a payload in the same format as in <xref target="deleting-an-account"/>. The only
difference is that the value of the “resource” field is “authz”.</t>
<figure><artwork><![CDATA[
POST /acme/authz/asdf HTTP/1.1
Host: example.com
{
"resource": "authz",
"delete": true,
}
/* Signed as JWS */
]]></artwork></figure>
<t>The server MUST perform the same validity checks as in <xref target="deleting-an-account"/>
and reject the request if they fail. If the server deletes the account then it
MUST send a response with a 200 (OK) status code and an empty body.</t>
</section>
</section>
<section anchor="certificate-issuance" title="Certificate Issuance">
<t>The holder of an account key pair authorized for one or more identifiers may use
ACME to request that a certificate be issued for any subset of those
identifiers. The client makes this request by sending a POST request to the
server’s new-certificate resource. The body of the POST is a JWS object whose
JSON payload contains a Certificate Signing Request (CSR) <xref target="RFC2986"/>. The CSR
encodes the parameters of the requested certificate; authority to issue is
demonstrated by the JWS signature by an account key, from which the server can
look up related authorizations. Some attributes which cannot be reflected in a
CSR are placed directly in the certificate request.</t>
<t><list style="hanging">
<t hangText='csr (required, string):'>
A CSR encoding the parameters for the certificate being requested. The CSR is
sent in the Base64url-encoded version of the DER format. (Note: This field uses
the same modified Base64 encoding rules used elsewhere in this document, so it
is different from PEM.)</t>
<t hangText='notBefore (optional, string):'>
The requested value of the notBefore field in the certificate, in the date
format defined in <xref target="RFC3339"/></t>
<t hangText='notAfter (optional, string):'>
The requested value of the notAfter field in the certificate, in the date
format defined in <xref target="RFC3339"/></t>
</list></t>
<figure><artwork><![CDATA[
POST /acme/new-cert HTTP/1.1
Host: example.com
Accept: application/pkix-cert
{
"resource": "new-cert",
"csr": "5jNudRx6Ye4HzKEqT5...FS6aKdZeGsysoCo4H9P",
"notBefore": "2016-01-01T00:00:00Z",
"notAfter": "2016-01-08T00:00:00Z"
}
/* Signed as JWS */
]]></artwork></figure>
<t>The CSR encodes the client’s requests with regard to the content of the
certificate to be issued. The CSR MUST indicate the requested identifiers,
either in the commonName portion of the requested subject name, or in an
extensionRequest attribute <xref target="RFC2985"/> requesting a subjectAltName extension.</t>
<t>The values provided in the CSR are only a request, and are not guaranteed. The
server SHOULD return an error if it cannot fulfil the request as specified, but
MAY issue a certificate with contents other than those requested, according to
its local policy (e.g., removing identifiers for which the client is not
authorized).</t>
<t>It is up to the server’s local policy to decide which names are acceptable in a
certificate, given the authorizations that the server associates with the
client’s account key. A server MAY consider a client authorized for a wildcard
domain if it is authorized for the underlying domain name (without the “*”
label). Servers SHOULD NOT extend authorization across identifier types. For
example, if a client is authorized for “example.com”, then the server should not
allow the client to issue a certificate with an iPAddress subjectAltName, even
if it contains an IP address to which example.com resolves.</t>
<t>If the CA decides to issue a certificate, then the server creates a new
certificate resource and returns a URI for it in the Location header field of a
201 (Created) response.</t>
<figure><artwork><![CDATA[
HTTP/1.1 201 Created
Location: https://example.com/acme/cert/asdf
]]></artwork></figure>
<t>If the certificate is available at the time of the response, it is provided in
the body of the response. If the CA has not yet issued the certificate, the
body of this response will be empty. The client should then send a GET request
to the certificate URI to poll for the certificate. As long as the certificate
is unavailable, the server MUST provide a 202 (Accepted) response and include a
Retry-After header to indicate when the server believes the certificate will be
issued (as in the example above).</t>
<figure><artwork><![CDATA[
GET /acme/cert/asdf HTTP/1.1
Host: example.com
Accept: application/pkix-cert
HTTP/1.1 202 Accepted
Retry-After: 120
]]></artwork></figure>
<t>The default format of the certificate is DER (application/pkix-cert). The
client may request other formats by including an Accept header in its request.</t>
<t>The server provides metadata about the certificate in HTTP headers. In
particular, the server MUST include a Link relation header field <xref target="RFC5988"/>
with relation “up” to provide a certificate under which this certificate was
issued, and one with relation “author” to indicate the registration under which
this certificate was issued.</t>
<t>The server MAY include an Expires header as a hint to the client about when to
renew the certificate. (Of course, the real expiration of the certificate is
controlled by the notAfter time in the certificate itself.)</t>
<t>If the CA participates in Certificate Transparency (CT) <xref target="RFC6962"/>, then they
may want to provide the client with a Signed Certificate Timestamp (SCT) that
can be used to prove that a certificate was submitted to a CT log. An SCT can
be included as an extension in the certificate or as an extension to OCSP
responses for the certificate. The server can also provide the client with
direct access to an SCT for a certificate using a Link relation header field
with relation “ct-sct”.</t>
<figure><artwork><![CDATA[
GET /acme/cert/asdf HTTP/1.1
Host: example.com
Accept: application/pkix-cert
HTTP/1.1 200 OK
Content-Type: application/pkix-cert
Link: <https://example.com/acme/ca-cert>;rel="up";title="issuer"
Link: <https://example.com/acme/revoke-cert>;rel="revoke"
Link: <https://example.com/acme/reg/asdf>;rel="author"
Link: <https://example.com/acme/sct/asdf>;rel="ct-sct"
Link: <https://example.com/acme/some-directory>;rel="directory"
Location: https://example.com/acme/cert/asdf
Content-Location: https://example.com/acme/cert-seq/12345
[DER-encoded certificate]
]]></artwork></figure>
<t>A certificate resource always represents the most recent certificate issued for
the name/key binding expressed in the CSR. If the CA allows a certificate to be
renewed, then it publishes renewed versions of the certificate through the same
certificate URI.</t>
<t>Clients retrieve renewed versions of the certificate using a GET query to the
certificate URI, which the server should then return in a 200 (OK) response.
The server SHOULD provide a stable URI for each specific certificate in the
Content-Location header field, as shown above. Requests to stable certificate
URIs MUST always result in the same certificate.</t>
<t>To avoid unnecessary renewals, the CA may choose not to issue a renewed
certificate until it receives such a request (if it even allows renewal at all).
In such cases, if the CA requires some time to generate the new certificate, the
CA MUST return a 202 (Accepted) response, with a Retry-After header field that
indicates when the new certificate will be available. The CA MAY include the
current (non-renewed) certificate as the body of the response.</t>
<t>Likewise, in order to prevent unnecessary renewal due to queries by parties
other than the account key holder, certificate URIs should be structured as
capability URLs <xref target="W3C.WD-capability-urls-20140218"/>.</t>
<t>From the client’s perspective, there is no difference between a certificate URI
that allows renewal and one that does not. If the client wishes to obtain a
renewed certificate, and a GET request to the certificate URI does not yield
one, then the client may initiate a new-certificate transaction to request one.</t>
</section>
<section anchor="certificate-revocation" title="Certificate Revocation">
<t>To request that a certificate be revoked, the client sends a POST request to
the ACME server’s revoke-cert URI. The body of the POST is a JWS object whose
JSON payload contains the certificate to be revoked:</t>
<t><list style="hanging">
<t hangText='certificate (required, string):'>
The certificate to be revoked, in the base64url-encoded version of the DER
format. (Note: This field uses the same modified Base64 encoding rules used
elsewhere in this document, so it is different from PEM.)</t>
</list></t>
<figure><artwork><![CDATA[
POST /acme/revoke-cert HTTP/1.1
Host: example.com
{
"resource": "revoke-cert",
"certificate": "MIIEDTCCAvegAwIBAgIRAP8..."
}
/* Signed as JWS */
]]></artwork></figure>
<t>Revocation requests are different from other ACME request in that they can be
signed either with an account key pair or the key pair in the certificate.
Before revoking a certificate, the server MUST verify that the key used to sign
the request is authorized to revoke the certificate. The server SHOULD consider
at least the following keys authorized for a given certificate:</t>
<t><list style="symbols">
<t>the public key in the certificate.</t>
<t>an account key that is authorized to act for all of the identifier(s) in the
certificate.</t>
</list></t>
<t>If the revocation succeeds, the server responds with status code 200 (OK). If
the revocation fails, the server returns an error.</t>
<figure><artwork><![CDATA[
HTTP/1.1 200 OK
Content-Length: 0
--- or ---
HTTP/1.1 403 Forbidden
Content-Type: application/problem+json
Content-Language: en
{
"type": "urn:ietf:params:acme:error:unauthorized"
"detail": "No authorization provided for name example.net"
"instance": "http://example.com/doc/unauthorized"
}
]]></artwork></figure>
</section>
</section>
<section anchor="identifier-validation-challenges" title="Identifier Validation Challenges">
<t>There are few types of identifiers in the world for which there is a standardized
mechanism to prove possession of a given identifier. In all practical cases,
CAs rely on a variety of means to test whether an entity applying for a
certificate with a given identifier actually controls that identifier.</t>
<t>Challenges provide the server with assurance that an account key holder is also
the entity that controls an identifier. For each type of challenge, it must be
the case that in order for an entity to successfully complete the challenge the
entity must both:</t>
<t><list style="symbols">
<t>Hold the private key of the account key pair used to respond to the challenge</t>
<t>Control the identifier in question</t>
</list></t>
<t><xref target="security-considerations"/> documents how the challenges defined in this
document meet these requirements. New challenges will need to document how they
do.</t>
<t>ACME uses an extensible challenge/response framework for identifier validation.
The server presents a set of challenge in the authorization object it sends to a
client (as objects in the “challenges” array), and the client responds by
sending a response object in a POST request to a challenge URI.</t>
<t>This section describes an initial set of challenge types. Each challenge must
describe:</t>
<t><list style="numbers">
<t>Content of challenge objects</t>
<t>Content of response objects</t>
<t>How the server uses the challenge and response to verify control of an
identifier</t>
</list></t>
<t>Challenge objects all contain the following basic fields:</t>
<t><list style="hanging">
<t hangText='type (required, string):'>
The type of challenge encoded in the object.</t>
<t hangText='uri (required, string):'>
The URI to which a response can be posted.</t>
<t hangText='status (required, string):'>
The status of this authorization. Possible values are: “pending”, “valid”,
and “invalid”. If this field is missing, then the default value is “pending”.</t>
<t hangText='validated (optional, string):'>
The time at which this challenge was completed by the server, encoded in the
format specified in RFC 3339 <xref target="RFC3339"/>. This field is REQUIRED if the
“status” field is “valid”.</t>
<t hangText='error (optional, dictionary of string):'>
The error that occurred while the server was validating the challenge, if any.
This field is structured as a problem document
<xref target="I-D.ietf-appsawg-http-problem"/>.</t>
</list></t>
<t>All additional fields are specified by the challenge type. If the server sets a
challenge’s “status” to “invalid”, it SHOULD also include the “error” field to
help the client diagnose why they failed the challenge.</t>
<t>Different challenges allow the server to obtain proof of different aspects of
control over an identifier. In some challenges, like HTTP and TLS SNI, the
client directly proves its ability to do certain things related to the
identifier. The choice of which challenges to offer to a client under which
circumstances is a matter of server policy.</t>
<t>The identifier validation challenges described in this section all relate to
validation of domain names. If ACME is extended in the future to support other
types of identifier, there will need to be new challenge types, and they will
need to specify which types of identifier they apply to.</t>
<t>[[ Editor’s Note: In pre-RFC versions of this specification, challenges are
labeled by type, and with the version of the draft in which they were
introduced. For example, if an HTTP challenge were introduced in version -03
and a breaking change made in version -05, then there would be a challenge
labeled “http-03” and one labeled “http-05” – but not one labeled “http-04”,
since challenge in version -04 was compatible with one in version -04. ]]</t>
<t>[[ Editor’s Note: Operators SHOULD NOT issue “combinations” arrays in
authorization objects that require the client to perform multiple challenges
over the same type, e.g., [“http-03”, “http-05”]. Challenges within a type are
testing the same capability of the domain owner, and it may not be possible to
satisfy both at once. ]]</t>
<section anchor="key-authorizations" title="Key Authorizations">
<t>Several of the challenges in this document makes use of a key authorization
string. A key authorization is a string that expresses a domain holder’s
authorization for a specified key to satisfy a specified challenge, by
concatenating the token for the challenge with a key fingerprint, separated by a
“.” character:</t>
<figure><artwork><![CDATA[
key-authz = token || '.' || base64url(JWK\_Thumbprint(accountKey))
]]></artwork></figure>
<t>The “JWK_Thumbprint” step indicates the computation specified in <xref target="RFC7638"/>,
using the SHA-256 digest. As specified in the individual challenges below, the
token for a challenge is a JSON string comprised entirely of characters in the
URL-safe Base64 alphabet. The “||” operator indicates concatenation of strings.</t>
<t>In computations involving key authorizations, such as the digest computations
required for the DNS and TLS SNI challenges, the key authorization string MUST
be represented in UTF-8 form (or, equivalently, ASCII).</t>
<t>An example of how to compute a JWK thumbprint can be found in Section 3.1 of
<xref target="RFC7638"/>. Note that some cryptographic libraries prepend a zero octet to the
representation of the RSA public key parameters N and E, in order to avoid
ambiguity with regard to the sign of the number. As noted in JWA <xref target="RFC7518"/>, a
JWK object MUST NOT include this zero octet. That is, any initial zero octets
MUST be stripped before the values are base64url-encoded.</t>
</section>
<section anchor="http" title="HTTP">
<t>With HTTP validation, the client in an ACME transaction proves its control over
a domain name by proving that it can provision resources on an HTTP server that
responds for that domain name. The ACME server challenges the client to
provision a file at a specific path, with a specific string as its content.</t>
<t>As a domain may resolve to multiple IPv4 and IPv6 addresses, the server will
connect to at least one of the hosts found in A and AAAA records. Because many
web servers allocate a default HTTPS virtual host to a particular low-privilege
tenant user in a subtle and non-intuitive manner, the challenge must be
completed over HTTP, not HTTPS.</t>
<t><list style="hanging">
<t hangText='type (required, string):'>
The string “http-01”</t>
<t hangText='token (required, string):'>
A random value that uniquely identifies the challenge. This value MUST have
at least 128 bits of entropy, in order to prevent an attacker from guessing it.
It MUST NOT contain any characters outside the URL-safe Base64 alphabet and MUST
NOT contain any padding characters (“=”).</t>
</list></t>
<figure><artwork><![CDATA[
{
"type": "http-01",
"token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA",
}
]]></artwork></figure>
<t>A client responds to this challenge by constructing a key authorization from
the “token” value provided in the challenge and the client’s account key. The
client then provisions the key authorization as a resource on the HTTP server
for the domain in question.</t>
<t>The path at which the resource is provisioned is comprised of the fixed prefix
“.well-known/acme-challenge/”, followed by the “token” value in the challenge.
The value of the resource MUST be the ASCII representation of the key
authorization.</t>
<figure><artwork><![CDATA[
.well-known/acme-challenge/evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA
]]></artwork></figure>
<t>The client’s response to this challenge indicates its agreement to this
challenge by sending the server the key authorization covering the challenge’s
token and the client’s account key. In addition, the client MAY advise the
server at which IP the challenge is provisioned.</t>
<t><list style="hanging">
<t hangText='keyAuthorization (required, string):'>
The key authorization for this challenge. This value MUST match the token
from the challenge and the client’s account key.</t>
<t hangText='address (optional, string):'>
An IPv4 or IPv6 address, in dotted decimal form or <xref target="RFC4291"/> form,
respectively. If given, this address MUST be included in the set of IP
addresses to which the domain name resolves when the server attempts validation.
If given, the server SHOULD connect to that specific IP address instead of
arbitrarily choosing an IP from the set of A and AAAA records to which the
domain name resolves.</t>
</list></t>
<figure><artwork><![CDATA[
{
"keyAuthorization": "evaGxfADs...62jcerQ"
}
/* Signed as JWS */
]]></artwork></figure>
<t>On receiving a response, the server MUST verify that the key authorization in
the response matches the “token” value in the challenge and the client’s account
key. If they do not match, then the server MUST return an HTTP error in
response to the POST request in which the client sent the challenge.</t>
<t>Given a challenge/response pair, the server verifies the client’s control of the
domain by verifying that the resource was provisioned as expected.</t>
<t><list style="numbers">
<t>Form a URI by populating the URI template <xref target="RFC6570"/>
“http://{domain}/.well-known/acme-challenge/{token}”, where:
<list style="symbols">
<t>the domain field is set to the domain name being verified; and</t>
<t>the token field is set to the token in the challenge.</t>
</list></t>
<t>Verify that the resulting URI is well-formed.</t>
<t>If the client has supplied an address to use, verify that the address is
included in the A or AAAA records to which the domain name resolves. If
the address is not included in the result, the validation fails.</t>
<t>Dereference the URI using an HTTP GET request. If an address was supplied
by the client, use that address to establish the HTTP connection.</t>
<t>Verify that the body of the response is well-formed key authorization. The
server SHOULD ignore whitespace characters at the end of the body.</t>
<t>Verify that key authorization provided by the server matches the token for
this challenge and the client’s account key.</t>
</list></t>
<t>If all of the above verifications succeed, then the validation is successful.
If the request fails, or the body does not pass these checks, then it has
failed.</t>
</section>
<section anchor="tls-with-server-name-indication-tls-sni" title="TLS with Server Name Indication (TLS SNI)">
<t>The TLS with Server Name Indication (TLS SNI) validation method
proves control over a domain name by requiring the client to configure a TLS
server referenced by an A/AAAA record under the domain name to respond to
specific connection attempts utilizing the Server Name Indication extension
<xref target="RFC6066"/>. The server verifies the client’s challenge by accessing the
reconfigured server and verifying a particular challenge certificate is
presented.</t>
<t><list style="hanging">
<t hangText='type (required, string):'>
The string “tls-sni-02”</t>
<t hangText='token (required, string):'>
A random value that uniquely identifies the challenge. This value MUST have
at least 128 bits of entropy, in order to prevent an attacker from guessing it.
It MUST NOT contain any characters outside the URL-safe Base64 alphabet and MUST
NOT contain any padding characters (“=”).</t>
</list></t>
<figure><artwork><![CDATA[
{
"type": "tls-sni-02",
"token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
}
]]></artwork></figure>
<t>A client responds to this challenge by constructing a self-signed certificate
which the client MUST provision at the domain name concerned in order to pass
the challenge.</t>
<t>The certificate may be constructed arbitrarily, except that each certificate
MUST have exactly two subjectAlternativeNames, SAN A and SAN B. Both MUST be
dNSNames.</t>
<t>SAN A MUST be constructed as follows: compute the SHA-256 digest of the
UTF-8-encoded challenge token and encode it in lowercase hexadecimal form. The
dNSName is “x.y.token.acme.invalid”, where x is the first half of the
hexadecimal representation and y is the second half.</t>
<t>SAN B MUST be constructed as follows: compute the SHA-256 digest of
the UTF-8 encoded key authorization and encode it in lowercase hexadecimal
form. The dNSName is “x.y.ka.acme.invalid” where x is the first half of the
hexadecimal representation and y is the second half.</t>
<t>The client MUST ensure that the certificate is served to TLS connections
specifying a Server Name Indication (SNI) value of SAN A.</t>
<t>The response to the TLS-SNI challenge simply acknowledges that the client is
ready to fulfill this challenge.</t>
<t><list style="hanging">
<t hangText='keyAuthorization (required, string):'>
The key authorization for this challenge. This value MUST match the token
from the challenge and the client’s account key.</t>
</list></t>
<figure><artwork><![CDATA[
{
"keyAuthorization": "evaGxfADs...62jcerQ",
}
/* Signed as JWS */
]]></artwork></figure>
<t>On receiving a response, the server MUST verify that the key authorization in
the response matches the “token” value in the challenge and the client’s account
key. If they do not match, then the server MUST return an HTTP error in
response to the POST request in which the client sent the challenge.</t>
<t>Given a challenge/response pair, the ACME server verifies the client’s control
of the domain by verifying that the TLS server was configured appropriately,
using these steps:</t>
<t><list style="numbers">
<t>Compute SAN A and SAN B in the same way as the client.</t>
<t>Open a TLS connection to the domain name being validated on the requested
port, presenting SAN A in the SNI field. In the ClientHello initiating the
TLS handshake, the server MUST include a server_name extension (i.e., SNI)
containing SAN A. The server SHOULD ensure that it does not reveal SAN B in
any way when making the TLS connection, such that the presentation of SAN B
in the returned certificate proves association with the client.</t>
<t>Verify that the certificate contains a subjectAltName extension containing
dNSName entries of SAN A and SAN B and no other entries.
The comparison MUST be insensitive to case and ordering of names.</t>
</list></t>
<t>It is RECOMMENDED that the ACME server validation TLS connections from multiple
vantage points to reduce the risk of DNS hijacking attacks.</t>
<t>If all of the above verifications succeed, then the validation is successful.
Otherwise, the validation fails.</t>
</section>
<section anchor="dns" title="DNS">
<t>When the identifier being validated is a domain name, the client can prove
control of that domain by provisioning a resource record under it. The DNS
challenge requires the client to provision a TXT record containing a designated
value under a specific validation domain name.</t>
<t><list style="hanging">
<t hangText='type (required, string):'>
The string “dns-01”</t>
<t hangText='token (required, string):'>
A random value that uniquely identifies the challenge. This value MUST have
at least 128 bits of entropy, in order to prevent an attacker from guessing it.
It MUST NOT contain any characters outside the URL-safe Base64 alphabet and MUST
NOT contain any padding characters (“=”).</t>
</list></t>
<figure><artwork><![CDATA[
{
"type": "dns-01",
"token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
}
]]></artwork></figure>
<t>A client responds to this challenge by constructing a key authorization from the
“token” value provided in the challenge and the client’s account key. The
client then computes the SHA-256 digest of the key authorization.</t>
<t>The record provisioned to the DNS is the base64url encoding of this digest. The
client constructs the validation domain name by prepending the label
“_acme-challenge” to the domain name being validated, then provisions a TXT
record with the digest value under that name. For example, if the domain name
being validated is “example.com”, then the client would provision the following
DNS record:</t>
<figure><artwork><![CDATA[
_acme-challenge.example.com. 300 IN TXT "gfj9Xq...Rg85nM"
]]></artwork></figure>
<t>The response to the DNS challenge provides the computed key authorization to
acknowledge that the client is ready to fulfill this challenge.</t>
<t><list style="hanging">
<t hangText='keyAuthorization (required, string):'>
The key authorization for this challenge. This value MUST match the token
from the challenge and the client’s account key.</t>
</list></t>
<figure><artwork><![CDATA[
{
"keyAuthorization": "evaGxfADs...62jcerQ",
}
/* Signed as JWS */
]]></artwork></figure>
<t>On receiving a response, the server MUST verify that the key authorization in
the response matches the “token” value in the challenge and the client’s account
key. If they do not match, then the server MUST return an HTTP error in
response to the POST request in which the client sent the challenge.</t>
<t>To validate a DNS challenge, the server performs the following steps:</t>
<t><list style="numbers">
<t>Compute the SHA-256 digest of the key authorization</t>
<t>Query for TXT records under the validation domain name</t>
<t>Verify that the contents of one of the TXT records matches the digest value</t>
</list></t>
<t>If all of the above verifications succeed, then the validation is successful.
If no DNS record is found, or DNS record and response payload do not pass these
checks, then the validation fails.</t>
</section>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<t>[[ Editor’s Note: Should we create a registry for tokens that go into the
various JSON objects used by this protocol, i.e., the field names in the JSON
objects? ]]</t>
</section>
<section anchor="well-known-uri-for-the-http-challenge" title="Well-Known URI for the HTTP Challenge">
<t>The “Well-Known URIs” registry should be updated with the following additional
value (using the template from <xref target="RFC5785"/>):</t>
<t>URI suffix: acme-challenge</t>
<t>Change controller: IETF</t>
<t>Specification document(s): This document, Section <xref target="http"/></t>
<t>Related information: N/A</t>
<section anchor="replay-nonce-http-header" title="Replay-Nonce HTTP Header">
<t>The “Message Headers” registry should be updated with the following additional
value:</t>
<t>| Header Field Name | Protocol | Status | Reference |
+:——————+:———+:———+:—————–+
| Replay-Nonce | http | standard | <xref target="replay-nonce"/> |</t>
</section>
<section anchor="nonce-jws-header-parameter" title="“nonce” JWS Header Parameter">
<t>The “JSON Web Signature and Encryption Header Parameters” registry should be
updated with the following additional value:</t>
<t><list style="symbols">
<t>Header Parameter Name: “nonce”</t>
<t>Header Parameter Description: Nonce</t>
<t>Header Parameter Usage Location(s): JWE, JWS</t>
<t>Change Controller: IESG</t>
<t>Specification Document(s): <xref target="nonce-nonce-jws-header-parameter"/> of
RFC XXXX</t>
</list></t>
<t>[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned to this
document ]]</t>
</section>
<section anchor="urn-sub-namespace-for-acme-urnietfparamsacme" title="URN Sub-namespace for ACME (urn:ietf:params:acme)">
<t>The “IETF URN Sub-namespace for Registered Protocol Parameter Identifiers”
registry should be updated with the following additional value, following the
template in <xref target="RFC3553"/>:</t>
<t><list style="hanging">
<t hangText='Registry name:'>
acme</t>
<t hangText='Specification:'>
RFC XXXX</t>
<t hangText='Repository:'>
URL-TBD</t>
<t hangText='Index value:'>
No transformation needed. The</t>
</list></t>
<t>[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned to this
document, and replace URL-TBD with the URL assigned by IANA for registries of
ACME parameters. ]]</t>
</section>
<section anchor="new-registries" title="New Registries">
<t>This document requests that IANA create three new registries:</t>
<t><list style="numbers">
<t>ACME Error Codes</t>
<t>ACME Identifier Types</t>
<t>ACME Challenge Types</t>
</list></t>
<t>All of these registries should be administered under a Specification Required
policy <xref target="RFC5226"/>.</t>
<section anchor="error-codes" title="Error Codes">
<t>This registry lists values that are used within URN values that are provided in
the “type” field of problem documents in ACME.</t>
<t>Template:</t>
<t><list style="symbols">
<t>Code: The label to be included in the URN for this error, following
“urn:ietf:params:acme:”</t>
<t>Description: A human-readable description of the error</t>
<t>Reference: Where the error is defined</t>
</list></t>
<t>Initial contents: The codes and descriptions in the table in <xref target="errors"/> above,
with the Reference field set to point to this specification.</t>
</section>
<section anchor="identifier-types" title="Identifier Types">
<t>This registry lists the types of identifiers that ACME clients may request
authorization to issue in certificates.</t>
<t>Template:</t>
<t><list style="symbols">
<t>Label: The value to be put in the “type” field of the identifier object</t>
<t>Reference: Where the identifier type is defined</t>
</list></t>
<t>Initial contents:</t>
<texttable>
<ttcol align='left'>Label</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>dns</c>
<c>RFC XXXX</c>
</texttable>
<t>[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned to this
document ]]</t>
</section>
<section anchor="challenge-types" title="Challenge Types">
<t>This registry lists the ways that ACME servers can offer to validate control of
an identifier. The “Identifier Type” field in template MUST be contained in the
Label column of the ACME Identifier Types registry.</t>
<t>Template:</t>
<t><list style="symbols">
<t>Label: The value to be put in the “type” field of challenge objects using this
validation mechanism</t>
<t>Identifier Type: The type of identifier that this mechanism applies to</t>
<t>Reference: Where the challenge type is defined</t>
</list></t>
<t>Initial Contents</t>
<texttable>
<ttcol align='left'>Label</ttcol>
<ttcol align='left'>Identifier Type</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>http</c>
<c>dns</c>
<c>RFC XXXX</c>
<c>tls-sni</c>
<c>dns</c>
<c>RFC XXXX</c>
<c>dns</c>
<c>dns</c>
<c>RFC XXXX</c>
</texttable>
<t>[[ RFC EDITOR: Please replace XXXX above with the RFC number assigned to this
document ]]</t>
</section>
</section>
</section>
<section anchor="security-considerations" title="Security Considerations">
<t>ACME is a protocol for managing certificates that attest to identifier/key
bindings. Thus the foremost security goal of ACME is to ensure the integrity of
this process, i.e., to ensure that the bindings attested by certificates are
correct, and that only authorized entities can manage certificates. ACME
identifies clients by their account keys, so this overall goal breaks down into
two more precise goals:</t>
<t><list style="numbers">
<t>Only an entity that controls an identifier can get an account key authorized
for that identifier</t>
<t>Once authorized, an account key’s authorizations cannot be improperly
transferred to another account key</t>
</list></t>
<t>In this section, we discuss the threat model that underlies ACME and the ways
that ACME achieves these security goals within that threat model. We also
discuss the denial-of-service risks that ACME servers face, and a few other
miscellaneous considerations.</t>
<section anchor="threat-model" title="Threat model">
<t>As a service on the Internet, ACME broadly exists within the Internet threat
model <xref target="RFC3552"/>. In analyzing ACME, it is useful to think of an ACME server
interacting with other Internet hosts along three “channels”:</t>
<t><list style="symbols">
<t>An ACME channel, over which the ACME HTTPS requests are exchanged</t>
<t>A validation channel, over which the ACME server performs additional requests
to validate a client’s control of an identifier</t>
<t>A contact channel, over which the ACME server sends messages to the registered
contacts for ACME clients</t>
</list></t>
<figure><artwork><![CDATA[
+------------+
| ACME | ACME Channel
| Client |--------------------+
+------------+ |
^ V
| Contact Channel +------------+
+--------------------| ACME |
| Server |
+------------+
+------------+ |
| Validation |<-------------------+
| Server | Validation Channel
+------------+
]]></artwork></figure>
<t>In practice, the risks to these channels are not entirely separate, but they are
different in most cases. Each of the three channels, for example, uses a
different communications pattern: the ACME channel will comprise inbound HTTPS
connections to the ACME server, the validation channel outbound HTTP or DNS
requests, and the contact channel will use channels such as email and PSTN.</t>
<t>Broadly speaking, ACME aims to be secure against active and passive attackers on
any individual channel. Some vulnerabilities arise (noted below), when an
attacker can exploit both the ACME channel and one of the others.</t>
<t>On the ACME channel, in addition to network-layer attackers, we also need to
account for application-layer man in the middle attacks, and for abusive use of
the protocol itself. Protection against application-layer MitM addresses
potential attackers such as Content Distribution Networks (CDNs) and middleboxes
with a TLS MitM function. Preventing abusive use of ACME means ensuring that an
attacker with access to the validation or contact channels can’t obtain
illegitimate authorization by acting as an ACME client (legitimately, in terms
of the protocol).</t>
</section>
<section anchor="integrity-of-authorizations" title="Integrity of Authorizations">
<t>ACME allows anyone to request challenges for an identifier by registering an
account key and sending a new-authorization request under that account key. The
integrity of the authorization process thus depends on the identifier validation
challenges to ensure that the challenge can only be completed by someone who
both (1) holds the private key of the account key pair, and (2) controls the
identifier in question.</t>
<t>Validation responses need to be bound to an account key pair in order to avoid
situations where an ACME MitM can switch out a legitimate domain holder’s
account key for one of his choosing, e.g.:</t>
<t><list style="symbols">
<t>Legitimate domain holder registers account key pair A</t>
<t>MitM registers account key pair B</t>
<t>Legitimate domain holder sends a new-authorization request signed under
account key A</t>
<t>MitM suppresses the legitimate request, but sends the same request signed
under account key B</t>
<t>ACME server issues challenges and MitM forwards them to the legitimate domain
holder</t>
<t>Legitimate domain holder provisions the validation response</t>
<t>ACME server performs validation query and sees the response provisioned by the
legitimate domain holder</t>
<t>Because the challenges were issued in response to a message signed account key
B, the ACME server grants authorization to account key B (the MitM) instead of
account key A (the legitimate domain holder)</t>
</list></t>
<t>All of the challenges above that require an out-of-band query by the server have
a binding to the account private key, such that only the account private key
holder can successfully respond to the validation query:</t>
<t><list style="symbols">
<t>HTTP: The value provided in the validation request is signed by the
account private key.</t>
<t>TLS SNI: The validation TLS request uses the account key pair as the server’s
key pair.</t>
<t>DNS: The MAC covers the account key, and the MAC key is derived from an ECDH
public key signed with the account private key.</t>
</list></t>
<t>The association of challenges to identifiers is typically done by requiring the
client to perform some action that only someone who effectively controls the
identifier can perform. For the challenges in this document, the actions are:</t>
<t><list style="symbols">
<t>HTTP: Provision files under .well-known on a web server for the domain</t>
<t>TLS SNI: Configure a TLS server for the domain</t>
<t>DNS: Provision DNS resource records for the domain</t>
</list></t>
<t>There are several ways that these assumptions can be violated, both by
misconfiguration and by attack. For example, on a web server that allows
non-administrative users to write to .well-known, any user can claim to own the
server’s hostname by responding to an HTTP challenge, and likewise for TLS
configuration and TLS SNI.</t>
<t>The use of hosting providers is a particular risk for ACME validation. If the
owner of the domain has outsourced operation of DNS or web services to a hosting
provider, there is nothing that can be done against tampering by the hosting
provider. As far as the outside world is concerned, the zone or web site
provided by the hosting provider is the real thing.</t>
<t>More limited forms of delegation can also lead to an unintended party gaining
the ability to successfully complete a validation transaction. For example,
suppose an ACME server follows HTTP redirects in HTTP validation and a
web site operator provisions a catch-all redirect rule that redirects requests
for unknown resources to different domain. Then the target of the redirect
could use that to get a certificate through HTTP validation, since the
validation path will not be known to the primary server.</t>
<t>The DNS is a common point of vulnerability for all of these challenges. An
entity that can provision false DNS records for a domain can attack the DNS
challenge directly, and can provision false A/AAAA records to direct the ACME
server to send its TLS SNI or HTTP validation query to a server of the
attacker’s choosing. There are a few different mitigations that ACME servers
can apply:</t>
<t><list style="symbols">
<t>Always querying the DNS using a DNSSEC-validating resolver (enhancing
security for zones that are DNSSEC-enabled)</t>
<t>Querying the DNS from multiple vantage points to address local attackers</t>
<t>Applying mitigations against DNS off-path attackers, e.g., adding entropy to
requests <xref target="I-D.vixie-dnsext-dns0x20"/> or only using TCP</t>
</list></t>
<t>Given these considerations, the ACME validation process makes it impossible for
any attacker on the ACME channel, or a passive attacker on the validation
channel to hijack the authorization process to authorize a key of the attacker’s
choice.</t>
<t>An attacker that can only see the ACME channel would need to convince the
validation server to provide a response that would authorize the attacker’s
account key, but this is prevented by binding the validation response to the
account key used to request challenges. A passive attacker on the validation
channel can observe the correct validation response and even replay it, but that
response can only be used with the account key for which it was generated.</t>
<t>An active attacker on the validation channel can subvert the ACME process, by
performing normal ACME transactions and providing a validation response for his
own account key. The risks due to hosting providers noted above are a
particular case. For identifiers where the server already has some public key
associated with the domain this attack can be prevented by requiring the client
to prove control of the corresponding private key.</t>
</section>
<section anchor="denial-of-service-considerations" title="Denial-of-Service Considerations">
<t>As a protocol run over HTTPS, standard considerations for TCP-based and
HTTP-based DoS mitigation also apply to ACME.</t>
<t>At the application layer, ACME requires the server to perform a few potentially
expensive operations. Identifier validation transactions require the ACME
server to make outbound connections to potentially attacker-controlled servers,
and certificate issuance can require interactions with cryptographic hardware.</t>
<t>In addition, an attacker can also cause the ACME server to send validation
requests to a domain of its choosing by submitting authorization requests for
the victim domain.</t>
<t>All of these attacks can be mitigated by the application of appropriate rate
limits. Issues closer to the front end, like POST body validation, can be
addressed using HTTP request limiting. For validation and certificate requests,
there are other identifiers on which rate limits can be keyed. For example, the
server might limit the rate at which any individual account key can issue
certificates, or the rate at which validation can be requested within a given
subtree of the DNS.</t>
</section>
<section anchor="ca-policy-considerations" title="CA Policy Considerations">
<t>The controls on issuance enabled by ACME are focused on validating that a
certificate applicant controls the identifier he claims. Before issuing a
certificate, however, there are many other checks that a CA might need to
perform, for example:</t>
<t><list style="symbols">
<t>Has the client agreed to a subscriber agreement?</t>
<t>Is the claimed identifier syntactically valid?</t>
<t>For domain names:
<list style="symbols">
<t>If the leftmost label is a ‘*’, then have the appropriate checks been
applied?</t>
<t>Is the name on the Public Suffix List?</t>
<t>Is the name a high-value name?</t>
<t>Is the name a known phishing domain?</t>
</list></t>
<t>Is the key in the CSR sufficiently strong?</t>
<t>Is the CSR signed with an acceptable algorithm?</t>
</list></t>
<t>CAs that use ACME to automate issuance will need to ensure that their servers
perform all necessary checks before issuing.</t>
</section>
</section>
<section anchor="operational-considerations" title="Operational Considerations">
<t>There are certain factors that arise in operational reality that operators of
ACME-based CAs will need to keep in mind when configuring their services.
For example:</t>
<t><list style="symbols">
<t>It is advisable to perform DNS queries via TCP to mitigate DNS forgery
attacks over UDP</t>
</list></t>
<t>[[ TODO: Other operational considerations ]]</t>
<section anchor="default-virtual-hosts" title="Default Virtual Hosts">
<t>In many cases, TLS-based services are deployed on hosted platforms that use
the Server Name Indication (SNI) TLS extension to distinguish between
different hosted services or “virtual hosts”. When a client initiates a
TLS connection with an SNI value indicating a provisioned host, the hosting
platform routes the connection to that host.</t>
<t>When a connection come in with an unknown SNI value, one might expect the
hosting platform to terminate the TLS connection. However, some hosting
platforms will choose a virtual host to be the “default”, and route connections
with unknown SNI values to that host.</t>
<t>In such cases, the owner of the default virtual host can complete a TLS-based challenge (e.g., “tls-sni-02”)
for any domain with an A record that points to the hosting platform. This could
result in mis-issuance in cases where there are multiple hosts with different
owners resident on the hosting platform.</t>
<t>A CA that accepts TLS-based proof of domain control should attempt to check
whether a domain is hosted on a domain with a default virtual host before
allowing an authorization request for this host to use a TLS-based challenge.
A default virtual host can be detected by initiating TLS connections to the host
with random SNI values within the namespace used for the TLS-based challenge
(the “acme.invalid” namespace for “tls-sni-02”).</t>
</section>
<section anchor="use-of-dnssec-resolvers" title="Use of DNSSEC Resolvers">
<t>An ACME-based CA will often need to make DNS queries, e.g., to validate control
of DNS names. Because the security of such validations ultimately depends on
the authenticity of DNS data, every possible precaution should be taken to
secure DNS queries done by the CA. It is therefore RECOMMENDED that ACME-based
CAs make all DNS queries via DNSSEC-validating stub or recursive resolvers. This
provides additional protection to domains which choose to make use of DNSSEC.</t>
<t>An ACME-based CA must use only a resolver if it trusts the resolver and every
component of the network route by which it is accessed. It is therefore
RECOMMENDED that ACME-based CAs operate their own DNSSEC-validating resolvers
within their trusted network and use these resolvers both for both CAA record
lookups and all record lookups in furtherance of a challenge scheme (A, AAAA,
TXT, etc.).</t>
</section>
</section>
<section anchor="acknowledgements" title="Acknowledgements">
<t>In addition to the editors listed on the front page, this document has benefited
from contributions from a broad set of contributors, all the way back to its
inception.</t>
<t><list style="symbols">
<t>Peter Eckersley, EFF</t>
<t>Eric Rescorla, Mozilla</t>
<t>Seth Schoen, EFF</t>
<t>Alex Halderman, University of Michigan</t>
<t>Martin Thomson, Mozilla</t>
<t>Jakub Warmuz, University of Oxford</t>
</list></t>
<t>This document draws on many concepts established by Eric Rescorla’s “Automated
Certificate Issuance Protocol” draft. Martin Thomson provided helpful guidance
in the use of HTTP.</t>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor='RFC2119' target='http://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>
<reference anchor='RFC2314' target='http://www.rfc-editor.org/info/rfc2314'>
<front>
<title>PKCS #10: Certification Request Syntax Version 1.5</title>
<author initials='B.' surname='Kaliski' fullname='B. Kaliski'><organization /></author>
<date year='1998' month='March' />
<abstract><t>This document describes a syntax for certification requests. This memo provides information for the Internet community. It does not specify an Internet standard of any kind.</t></abstract>
</front>
<seriesInfo name='RFC' value='2314'/>
<seriesInfo name='DOI' value='10.17487/RFC2314'/>
</reference>
<reference anchor='RFC2818' target='http://www.rfc-editor.org/info/rfc2818'>
<front>
<title>HTTP Over TLS</title>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<date year='2000' month='May' />
<abstract><t>This memo describes how to use Transport Layer Security (TLS) to secure Hypertext Transfer Protocol (HTTP) connections over the Internet. This memo provides information for the Internet community.</t></abstract>
</front>
<seriesInfo name='RFC' value='2818'/>
<seriesInfo name='DOI' value='10.17487/RFC2818'/>
</reference>
<reference anchor='RFC2985' target='http://www.rfc-editor.org/info/rfc2985'>
<front>
<title>PKCS #9: Selected Object Classes and Attribute Types Version 2.0</title>
<author initials='M.' surname='Nystrom' fullname='M. Nystrom'><organization /></author>
<author initials='B.' surname='Kaliski' fullname='B. Kaliski'><organization /></author>
<date year='2000' month='November' />
<abstract><t>This memo represents a republication of PKCS #9 v2.0 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from that specification. This memo provides information for the Internet community.</t></abstract>
</front>
<seriesInfo name='RFC' value='2985'/>
<seriesInfo name='DOI' value='10.17487/RFC2985'/>
</reference>
<reference anchor='RFC2986' target='http://www.rfc-editor.org/info/rfc2986'>
<front>
<title>PKCS #10: Certification Request Syntax Specification Version 1.7</title>
<author initials='M.' surname='Nystrom' fullname='M. Nystrom'><organization /></author>
<author initials='B.' surname='Kaliski' fullname='B. Kaliski'><organization /></author>
<date year='2000' month='November' />
<abstract><t>This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document. This memo provides information for the Internet community.</t></abstract>
</front>
<seriesInfo name='RFC' value='2986'/>
<seriesInfo name='DOI' value='10.17487/RFC2986'/>
</reference>
<reference anchor='RFC3339' target='http://www.rfc-editor.org/info/rfc3339'>
<front>
<title>Date and Time on the Internet: Timestamps</title>
<author initials='G.' surname='Klyne' fullname='G. Klyne'><organization /></author>
<author initials='C.' surname='Newman' fullname='C. Newman'><organization /></author>
<date year='2002' month='July' />
</front>
<seriesInfo name='RFC' value='3339'/>
<seriesInfo name='DOI' value='10.17487/RFC3339'/>
</reference>
<reference anchor='RFC3553' target='http://www.rfc-editor.org/info/rfc3553'>
<front>
<title>An IETF URN Sub-namespace for Registered Protocol Parameters</title>
<author initials='M.' surname='Mealling' fullname='M. Mealling'><organization /></author>
<author initials='L.' surname='Masinter' fullname='L. Masinter'><organization /></author>
<author initials='T.' surname='Hardie' fullname='T. Hardie'><organization /></author>
<author initials='G.' surname='Klyne' fullname='G. Klyne'><organization /></author>
<date year='2003' month='June' />
<abstract><t>This document describes a new sub-delegation for the 'ietf' URN namespace for registered protocol items. The 'ietf' URN namespace is defined in RFC 2648 as a root for persistent URIs that refer to IETF- defined resources. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='73'/>
<seriesInfo name='RFC' value='3553'/>
<seriesInfo name='DOI' value='10.17487/RFC3553'/>
</reference>
<reference anchor='RFC4291' target='http://www.rfc-editor.org/info/rfc4291'>
<front>
<title>IP Version 6 Addressing Architecture</title>
<author initials='R.' surname='Hinden' fullname='R. Hinden'><organization /></author>
<author initials='S.' surname='Deering' fullname='S. Deering'><organization /></author>
<date year='2006' month='February' />
<abstract><t>This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses.</t><t>This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4291'/>
<seriesInfo name='DOI' value='10.17487/RFC4291'/>
</reference>
<reference anchor='RFC4648' target='http://www.rfc-editor.org/info/rfc4648'>
<front>
<title>The Base16, Base32, and Base64 Data Encodings</title>
<author initials='S.' surname='Josefsson' fullname='S. Josefsson'><organization /></author>
<date year='2006' month='October' />
<abstract><t>This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4648'/>
<seriesInfo name='DOI' value='10.17487/RFC4648'/>
</reference>
<reference anchor='RFC5226' target='http://www.rfc-editor.org/info/rfc5226'>
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials='T.' surname='Narten' fullname='T. Narten'><organization /></author>
<author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'><organization /></author>
<date year='2008' month='May' />
<abstract><t>Many protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).</t><t>In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.</t><t>This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='26'/>
<seriesInfo name='RFC' value='5226'/>
<seriesInfo name='DOI' value='10.17487/RFC5226'/>
</reference>
<reference anchor='RFC5246' target='http://www.rfc-editor.org/info/rfc5246'>
<front>
<title>The Transport Layer Security (TLS) Protocol Version 1.2</title>
<author initials='T.' surname='Dierks' fullname='T. Dierks'><organization /></author>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<date year='2008' month='August' />
<abstract><t>This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5246'/>
<seriesInfo name='DOI' value='10.17487/RFC5246'/>
</reference>
<reference anchor='RFC5280' target='http://www.rfc-editor.org/info/rfc5280'>
<front>
<title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title>
<author initials='D.' surname='Cooper' fullname='D. Cooper'><organization /></author>
<author initials='S.' surname='Santesson' fullname='S. Santesson'><organization /></author>
<author initials='S.' surname='Farrell' fullname='S. Farrell'><organization /></author>
<author initials='S.' surname='Boeyen' fullname='S. Boeyen'><organization /></author>
<author initials='R.' surname='Housley' fullname='R. Housley'><organization /></author>
<author initials='W.' surname='Polk' fullname='W. Polk'><organization /></author>
<date year='2008' month='May' />
<abstract><t>This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5280'/>
<seriesInfo name='DOI' value='10.17487/RFC5280'/>
</reference>
<reference anchor='RFC5785' target='http://www.rfc-editor.org/info/rfc5785'>
<front>
<title>Defining Well-Known Uniform Resource Identifiers (URIs)</title>
<author initials='M.' surname='Nottingham' fullname='M. Nottingham'><organization /></author>
<author initials='E.' surname='Hammer-Lahav' fullname='E. Hammer-Lahav'><organization /></author>
<date year='2010' month='April' />
<abstract><t>This memo defines a path prefix for "well-known locations", "/.well-known/", in selected Uniform Resource Identifier (URI) schemes. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5785'/>
<seriesInfo name='DOI' value='10.17487/RFC5785'/>
</reference>
<reference anchor='RFC5988' target='http://www.rfc-editor.org/info/rfc5988'>
<front>
<title>Web Linking</title>
<author initials='M.' surname='Nottingham' fullname='M. Nottingham'><organization /></author>
<date year='2010' month='October' />
<abstract><t>This document specifies relation types for Web links, and defines a registry for them. It also defines the use of such links in HTTP headers with the Link header field. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5988'/>
<seriesInfo name='DOI' value='10.17487/RFC5988'/>
</reference>
<reference anchor='RFC6066' target='http://www.rfc-editor.org/info/rfc6066'>
<front>
<title>Transport Layer Security (TLS) Extensions: Extension Definitions</title>
<author initials='D.' surname='Eastlake 3rd' fullname='D. Eastlake 3rd'><organization /></author>
<date year='2011' month='January' />
<abstract><t>This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6066'/>
<seriesInfo name='DOI' value='10.17487/RFC6066'/>
</reference>
<reference anchor='RFC6570' target='http://www.rfc-editor.org/info/rfc6570'>
<front>
<title>URI Template</title>
<author initials='J.' surname='Gregorio' fullname='J. Gregorio'><organization /></author>
<author initials='R.' surname='Fielding' fullname='R. Fielding'><organization /></author>
<author initials='M.' surname='Hadley' fullname='M. Hadley'><organization /></author>
<author initials='M.' surname='Nottingham' fullname='M. Nottingham'><organization /></author>
<author initials='D.' surname='Orchard' fullname='D. Orchard'><organization /></author>
<date year='2012' month='March' />
<abstract><t>A URI Template is a compact sequence of characters for describing a range of Uniform Resource Identifiers through variable expansion. This specification defines the URI Template syntax and the process for expanding a URI Template into a URI reference, along with guidelines for the use of URI Templates on the Internet. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6570'/>
<seriesInfo name='DOI' value='10.17487/RFC6570'/>
</reference>
<reference anchor='RFC6844' target='http://www.rfc-editor.org/info/rfc6844'>
<front>
<title>DNS Certification Authority Authorization (CAA) Resource Record</title>
<author initials='P.' surname='Hallam-Baker' fullname='P. Hallam-Baker'><organization /></author>
<author initials='R.' surname='Stradling' fullname='R. Stradling'><organization /></author>
<date year='2013' month='January' />
<abstract><t>The Certification Authority Authorization (CAA) DNS Resource Record allows a DNS domain name holder to specify one or more Certification Authorities (CAs) authorized to issue certificates for that domain. CAA Resource Records allow a public Certification Authority to implement additional controls to reduce the risk of unintended certificate mis-issue. This document defines the syntax of the CAA record and rules for processing CAA records by certificate issuers. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6844'/>
<seriesInfo name='DOI' value='10.17487/RFC6844'/>
</reference>
<reference anchor='RFC6962' target='http://www.rfc-editor.org/info/rfc6962'>
<front>
<title>Certificate Transparency</title>
<author initials='B.' surname='Laurie' fullname='B. Laurie'><organization /></author>
<author initials='A.' surname='Langley' fullname='A. Langley'><organization /></author>
<author initials='E.' surname='Kasper' fullname='E. Kasper'><organization /></author>
<date year='2013' month='June' />
<abstract><t>This document describes an experimental protocol for publicly logging the existence of Transport Layer Security (TLS) certificates as they are issued or observed, in a manner that allows anyone to audit certificate authority (CA) activity and notice the issuance of suspect certificates as well as to audit the certificate logs themselves. The intent is that eventually clients would refuse to honor certificates that do not appear in a log, effectively forcing CAs to add all issued certificates to the logs.</t><t>Logs are network services that implement the protocol operations for submissions and queries that are defined in this document.</t></abstract>
</front>
<seriesInfo name='RFC' value='6962'/>
<seriesInfo name='DOI' value='10.17487/RFC6962'/>
</reference>
<reference anchor='RFC7159' target='http://www.rfc-editor.org/info/rfc7159'>
<front>
<title>The JavaScript Object Notation (JSON) Data Interchange Format</title>
<author initials='T.' surname='Bray' fullname='T. Bray' role='editor'><organization /></author>
<date year='2014' month='March' />
<abstract><t>JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.</t><t>This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.</t></abstract>
</front>
<seriesInfo name='RFC' value='7159'/>
<seriesInfo name='DOI' value='10.17487/RFC7159'/>
</reference>
<reference anchor='RFC7469' target='http://www.rfc-editor.org/info/rfc7469'>
<front>
<title>Public Key Pinning Extension for HTTP</title>
<author initials='C.' surname='Evans' fullname='C. Evans'><organization /></author>
<author initials='C.' surname='Palmer' fullname='C. Palmer'><organization /></author>
<author initials='R.' surname='Sleevi' fullname='R. Sleevi'><organization /></author>
<date year='2015' month='April' />
<abstract><t>This document defines a new HTTP header that allows web host operators to instruct user agents to remember ("pin") the hosts' cryptographic identities over a period of time. During that time, user agents (UAs) will require that the host presents a certificate chain including at least one Subject Public Key Info structure whose fingerprint matches one of the pinned fingerprints for that host. By effectively reducing the number of trusted authorities who can authenticate the domain during the lifetime of the pin, pinning may reduce the incidence of man-in-the-middle attacks due to compromised Certification Authorities.</t></abstract>
</front>
<seriesInfo name='RFC' value='7469'/>
<seriesInfo name='DOI' value='10.17487/RFC7469'/>
</reference>
<reference anchor='RFC7515' target='http://www.rfc-editor.org/info/rfc7515'>
<front>
<title>JSON Web Signature (JWS)</title>
<author initials='M.' surname='Jones' fullname='M. Jones'><organization /></author>
<author initials='J.' surname='Bradley' fullname='J. Bradley'><organization /></author>
<author initials='N.' surname='Sakimura' fullname='N. Sakimura'><organization /></author>
<date year='2015' month='May' />
<abstract><t>JSON Web Signature (JWS) represents content secured with digital signatures or Message Authentication Codes (MACs) using JSON-based data structures. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and an IANA registry defined by that specification. Related encryption capabilities are described in the separate JSON Web Encryption (JWE) specification.</t></abstract>
</front>
<seriesInfo name='RFC' value='7515'/>
<seriesInfo name='DOI' value='10.17487/RFC7515'/>
</reference>
<reference anchor='RFC7517' target='http://www.rfc-editor.org/info/rfc7517'>
<front>
<title>JSON Web Key (JWK)</title>
<author initials='M.' surname='Jones' fullname='M. Jones'><organization /></author>
<date year='2015' month='May' />
<abstract><t>A JSON Web Key (JWK) is a JavaScript Object Notation (JSON) data structure that represents a cryptographic key. This specification also defines a JWK Set JSON data structure that represents a set of JWKs. Cryptographic algorithms and identifiers for use with this specification are described in the separate JSON Web Algorithms (JWA) specification and IANA registries established by that specification.</t></abstract>
</front>
<seriesInfo name='RFC' value='7517'/>
<seriesInfo name='DOI' value='10.17487/RFC7517'/>
</reference>
<reference anchor='RFC7518' target='http://www.rfc-editor.org/info/rfc7518'>
<front>
<title>JSON Web Algorithms (JWA)</title>
<author initials='M.' surname='Jones' fullname='M. Jones'><organization /></author>
<date year='2015' month='May' />
<abstract><t>This specification registers cryptographic algorithms and identifiers to be used with the JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers.</t></abstract>
</front>
<seriesInfo name='RFC' value='7518'/>
<seriesInfo name='DOI' value='10.17487/RFC7518'/>
</reference>
<reference anchor='RFC7638' target='http://www.rfc-editor.org/info/rfc7638'>
<front>
<title>JSON Web Key (JWK) Thumbprint</title>
<author initials='M.' surname='Jones' fullname='M. Jones'><organization /></author>
<author initials='N.' surname='Sakimura' fullname='N. Sakimura'><organization /></author>
<date year='2015' month='September' />
<abstract><t>This specification defines a method for computing a hash value over a JSON Web Key (JWK). It defines which fields in a JWK are used in the hash computation, the method of creating a canonical form for those fields, and how to convert the resulting Unicode string into a byte sequence to be hashed. The resulting hash value can be used for identifying or selecting the key represented by the JWK that is the subject of the thumbprint.</t></abstract>
</front>
<seriesInfo name='RFC' value='7638'/>
<seriesInfo name='DOI' value='10.17487/RFC7638'/>
</reference>
<reference anchor='I-D.ietf-appsawg-http-problem'>
<front>
<title>Problem Details for HTTP APIs</title>
<author initials='m' surname='mnot' fullname='mnot'>
<organization />
</author>
<author initials='E' surname='Wilde' fullname='Erik Wilde'>
<organization />
</author>
<date month='January' day='19' year='2016' />
<abstract><t>This document defines a "problem detail" as a way to carry machine- readable details of errors in a HTTP response, to avoid the need to define new error response formats for HTTP APIs. Note to Readers This draft should be discussed on the apps-discuss mailing list [1]. This section is to be removed before publication. Note to RFC Editor Please replace all occurrences of "XXXX" with the final RFC number chosen for this draft. This section is to be removed before publication.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-appsawg-http-problem-03' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-appsawg-http-problem-03.txt' />
</reference>
</references>
<references title='Informative References'>
<reference anchor='RFC3552' target='http://www.rfc-editor.org/info/rfc3552'>
<front>
<title>Guidelines for Writing RFC Text on Security Considerations</title>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<author initials='B.' surname='Korver' fullname='B. Korver'><organization /></author>
<date year='2003' month='July' />
<abstract><t>All RFCs are required to have a Security Considerations section. Historically, such sections have been relatively weak. This document provides guidelines to RFC authors on how to write a good Security Considerations section. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='72'/>
<seriesInfo name='RFC' value='3552'/>
<seriesInfo name='DOI' value='10.17487/RFC3552'/>
</reference>
<reference anchor='W3C.CR-cors-20130129'
target='http://www.w3.org/TR/2013/CR-cors-20130129'>
<front>
<title>Cross-Origin Resource Sharing</title>
<author initials='A.' surname='Kesteren' fullname='Anne van Kesteren'>
<organization />
</author>
<date month='January' day='29' year='2013' />
</front>
<seriesInfo name='World Wide Web Consortium CR' value='CR-cors-20130129' />
<format type='HTML' target='http://www.w3.org/TR/2013/CR-cors-20130129' />
</reference>
<reference anchor='W3C.WD-capability-urls-20140218'
target='http://www.w3.org/TR/2014/WD-capability-urls-20140218'>
<front>
<title>Good Practices for Capability URLs</title>
<author initials='J.' surname='Tennison' fullname='Jeni Tennison'>
<organization />
</author>
<date month='February' day='18' year='2014' />
</front>
<seriesInfo name='World Wide Web Consortium WD' value='WD-capability-urls-20140218' />
<format type='HTML' target='http://www.w3.org/TR/2014/WD-capability-urls-20140218' />
</reference>
<reference anchor='I-D.vixie-dnsext-dns0x20'>
<front>
<title>Use of Bit 0x20 in DNS Labels to Improve Transaction Identity</title>
<author initials='P' surname='Vixie' fullname='Paul Vixie'>
<organization />
</author>
<author initials='D' surname='Dagon' fullname='David Dagon'>
<organization />
</author>
<date month='March' day='18' year='2008' />
<abstract><t>The small (16-bit) size of the DNS transaction ID has made it a frequent target for forgery, with the unhappy result of many cache pollution vulnerabilities demonstrated throughout Internet history. Even with perfectly and unpredictably random transaction ID's, random and birthday attacks are still theoretically feasible. This document describes a method by which an initiator can improve transaction identity using the 0x20 bit in DNS labels.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-vixie-dnsext-dns0x20-00' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-vixie-dnsext-dns0x20-00.txt' />
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 07:07:37 |