One document matched: draft-hammer-http-token-auth-00.txt
Network Working Group E. Hammer-Lahav
Internet-Draft Yahoo!
Intended status: Standards Track December 7, 2009
Expires: June 10, 2010
HTTP Authentication: Token Access Authentication
draft-hammer-http-token-auth-00
Abstract
This document specifies the HTTP Token Access Authentication scheme.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 10, 2010.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Hammer-Lahav Expires June 10, 2010 [Page 1]
Internet-Draft Token Authentication December 2009
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 6
2. Making Requests . . . . . . . . . . . . . . . . . . . . . . . 6
3. Verifying Requests . . . . . . . . . . . . . . . . . . . . . . 7
4. The WWW-Authenticate Response Header . . . . . . . . . . . . . 8
4.1. The 'class' Attribute . . . . . . . . . . . . . . . . . . 9
4.2. The 'method' Attribute . . . . . . . . . . . . . . . . . . 9
4.3. The 'coverage' Attribute . . . . . . . . . . . . . . . . . 9
4.4. The 'timestamp' Attribute . . . . . . . . . . . . . . . . 10
5. The Authorization Request Header . . . . . . . . . . . . . . . 10
5.1. The 'token' Attribute . . . . . . . . . . . . . . . . . . 11
5.2. The 'class' Attribute . . . . . . . . . . . . . . . . . . 11
5.3. The 'method' Attribute . . . . . . . . . . . . . . . . . . 11
5.4. The 'coverage' Attribute . . . . . . . . . . . . . . . . . 11
5.5. The 'nonce' Attribute . . . . . . . . . . . . . . . . . . 11
5.6. The 'timestamp' Attribute . . . . . . . . . . . . . . . . 11
5.7. The 'auth' Attribute . . . . . . . . . . . . . . . . . . . 11
6. The Authentication-Error Response Header . . . . . . . . . . . 11
6.1. The 'error-code' attribute . . . . . . . . . . . . . . . . 12
6.2. The 'error-info' attribute . . . . . . . . . . . . . . . . 12
6.3. The 'error-message' attribute . . . . . . . . . . . . . . 12
7. Authentication Methods . . . . . . . . . . . . . . . . . . . . 12
7.1. The 'none' Method . . . . . . . . . . . . . . . . . . . . 12
7.2. The 'hmac-sha-1' Method . . . . . . . . . . . . . . . . . 13
7.3. The 'hmac-sha-256' Method . . . . . . . . . . . . . . . . 13
7.4. The 'rsassa-pkcs1-v1.5-sha-256' Method . . . . . . . . . . 14
8. Coverage Methods . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. The 'base' Method . . . . . . . . . . . . . . . . . . . . 15
8.1.1. String Construction . . . . . . . . . . . . . . . . . 15
8.2. The 'base+body-hmac-sha-256' Method . . . . . . . . . . . 16
9. Scheme Extensions . . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10.1. Credentials Transmission . . . . . . . . . . . . . . . . . 17
10.2. Confidentiality of Requests . . . . . . . . . . . . . . . 17
10.3. Spoofing by Counterfeit Servers . . . . . . . . . . . . . 17
10.4. Plaintext Storage of Credentials . . . . . . . . . . . . . 17
10.5. Scoping of Access Requests . . . . . . . . . . . . . . . . 17
10.6. Entropy of Secrets . . . . . . . . . . . . . . . . . . . . 18
10.7. Denial of Service / Resource Exhaustion Attacks . . . . . 18
10.8. Coverage Limitations . . . . . . . . . . . . . . . . . . . 19
Hammer-Lahav Expires June 10, 2010 [Page 2]
Internet-Draft Token Authentication December 2009
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
Appendix A. Document History . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
13.1. Normative References . . . . . . . . . . . . . . . . . . . 19
13.2. Informative References . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
Hammer-Lahav Expires June 10, 2010 [Page 3]
Internet-Draft Token Authentication December 2009
1. Introduction
[[ This draft is submitted for the consideration of the OAuth Working
Group to be adopted as an official working group item per its current
charter. It is presented in its raw form to assist in facilitating a
more effective working group conversation and should not be
considered a complete proposal. Please discuss this draft on the
oauth@ietf.org [1] mailing list. ]]
With the growing use of distributed web services and cloud computing,
clients need to allow other parties access to the resources they
control. When granting access, clients should not be required to
share their credentials (typically a username and password), and
should have the ability to restrict access to a limited subset of the
resources they control or the access methods supported by these
resources. These goals require new classes of authentication
credentials.
The HTTP Basic and Digest Access authentication schemes defined by
[RFC2617], enable clients to make authenticated HTTP requests by
using a username (or userid) and a password. In most cases, the
client uses a single set of credentials to access all the resources
it controls which are hosted by the server.
While the Basic and Digest schemes can be used to send credentials
other than a username and password, their wide deployment and well-
established behavior in user-agents preclude them from being used
with other classes of credentials. Extending these schemes to
support new classes would require impractical changes to their
existing deployment.
The Token Access Authentication scheme provides a method for making
authenticated HTTP requests using a token - an identifier used to
denote an access grant with specific scope, duration, cryptographic
properties, and other attributes. Tokens can issued by the server,
self-issued by the client, or issued by a third party.
The token scheme support an extensible set of credential classes, by
enabling the server to declare the classes it supports. Token
classes determine how tokens are obtained and the context in which
they can be used. It also supports an extensible set of
authentication methods and authentication coverage (the elements of
the HTTP request such as the request URI or entity-body included in
the authentication process).
This specification defines four token authentication methods to
support the most common use cases and describes their security
properties. The methods through which clients obtain tokens
Hammer-Lahav Expires June 10, 2010 [Page 4]
Internet-Draft Token Authentication December 2009
supporting these methods are beyond the scope of this specification.
The OAuth protocol [I-D.ietf-oauth-web-delegation] defines one such
set of methods for obtaining oauth-class token credentials.
1.1. Terminology
client
An HTTP client (per [RFC2616]) capable of making Token-
authenticated requests (Section 2).
server
An HTTP server (per [RFC2616]) capable of accepting Token-
authenticated requests (Section 2).
protected resource
An access-restricted resource (per [RFC2616]) hosted by the
server and accessible by making a Token-authenticated request
(Section 2).
token credentials
A set of a unique identifier (token) and an authentication
method with an OPTIONAL shared secret (symmetric or
asymmetric), as well as other attributes (e.g. class, duration,
scope), used by the client to make authenticated requests.
normalized request string
A string representing various elements of the HTTP request,
normalized and concatenated together. The elements included in
the normalize request string are determined by the
authentication coverage supported by the server.
1.2. Example
The following HTTP request:
GET /resource/1 HTTP/1.1
Host: example.com
returns the following authentication challenge:
HTTP/1.1 401 Unauthorized
WWW-Authenticate: Token class="oauth",
methods="hmac-sha-1 hmac-sha-256",
timestamp="137131190"
This means the server is expecting an "oauth" class token using
Hammer-Lahav Expires June 10, 2010 [Page 5]
Internet-Draft Token Authentication December 2009
either the "hmac-sha-1" or "hmac-sha-256" authentication methods. It
also provides its current time to assist the client in synchronizing
its clock with the server's clock for the purpose of producing a
unique nonce value.
The client attempts the HTTP request again, this time using a set of
token credentials supporting the "hmac-sha-1" method issued by the
server earlier to authenticate:
GET /resource/1 HTTP/1.1
Host: example.com
Authorization: Token token="h480djs93hd8",
class="oauth",
method="hmac-sha-1",
timestamp="137131200",
nonce="dj83hs9s",
auth="djosJKDKJSD8743243/jdk33klY="
to which the server respond with the requested resource
representation after validating the request.
1.3. Notational Conventions
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 [RFC2119].
This document uses the Augmented Backus-Naur Form (ABNF) notation of
[I-D.ietf-httpbis-p1-messaging]. Additionally, the following rules
are included from [RFC2617]: realm, auth-param.
2. Making Requests
The client makes authenticated requests by calculating the values of
a set of attributes and adding them to the HTTP request using the
Authorization header field (Section 5). Authenticated request can be
sent either directly (without first receiving a challenge), or in
response to an authentication challenge.
To make an authenticated request, the client obtains information
about the attributes supported by the server. This information is
provided by the server via the WWW-Authenticate header field
(Section 4). The client SHOULD only send an authenticated request to
the server (without first receiving a challenge) if it has prior
knowledge of the attributes supported by server.
Hammer-Lahav Expires June 10, 2010 [Page 6]
Internet-Draft Token Authentication December 2009
The client chooses an available token with the supported class and
authentication method. It also chooses a supported authentication
coverage. The methods through which the client obtains a valid
token, or the criteria used to choose a token if more than one is
available are beyond the scope of this specification.
Once the client selects the appropriate token credentials it proceeds
to:
1. Assign values based on its selection to the following attributes:
* "token"
* "class"
* "method"
* "coverage"
2. If the client uses a coverage method other than "none" it MUST
assign values to the following attributes:
* "nonce"
* "timestamp"
3. Assigns value to any additional class-specific, method-specific,
or coverage-specific attributes as defined by protocol
extensions.
4. If the client uses a coverage method other than "none" it
constructs the normalized request string based on the selected
coverage as described in Section 8.
5. Calculates the value of the "auth" attribute as defined by the
selected authentication method.
6. Adds the assigned attributes to the request via the Authorization
header field (Section 5).
7. Sends the authenticated HTTP request to the server.
3. Verifying Requests
A servers receiving an authenticated request validates it by
performing the following REQUIRED steps:
Hammer-Lahav Expires June 10, 2010 [Page 7]
Internet-Draft Token Authentication December 2009
1. Verify that the token used by the client as well as the coverage
method matches the server's requirements.
2. If the client used a coverage method other than "none", construct
the normalized request string based on the selected coverage as
described in Section 8.
3. If the client used an authentication method other than "none",
recalculate the value of the "auth" attribute as described in
Section 7 and compare it to the value received from the client
via the "auth" attribute.
4. If the client used a coverage method other than "none", ensure
that the combination of nonce, timestamp, and token received from
the client has not been used before in a previous request (the
server MAY reject requests with stale timestamps; the
determination of staleness is left up to the server to define).
5. Verify the scope and status of the client credentials as
represented by the token.
If the request fails verification, the server SHOULD respond with an
HTTP 401 (unauthorized) status code, and SHOULD include a token
scheme authentication challenge using the WWW-Authenticate header
field (Section 6). The server MAY include further details about why
the request was rejected using the Authorization-Error header field
(Section 6).
4. The WWW-Authenticate Response Header
A server receiving a request for a protected resource without a valid
Authorization header field (Section 5) MUST respond with a 401 status
code (Unauthorized), and includes at least one "WWW-Authenticate"
header field including a token scheme challenge.
The "WWW-Authenticate" header field uses the framework defined by
[RFC2617] as follows:
Hammer-Lahav Expires June 10, 2010 [Page 8]
Internet-Draft Token Authentication December 2009
challenge = "Token" RWS token-challenge
token-challenge = class
CS method-list
[ CS coverage-list ]
[ CS timestamp ]
class = "class" "=" <"> token <">
method-list = "method" "=" <"> 1#method-name <">
method-name = "none" /
"hmac-sha-1" /
"hmac-sha-256" /
"rsassa-pkcs1-v1.5-sha-256" /
token
coverage-list = "coverage" "=" <"> 1#coverage-name <">
coverage-name = "none" /
"base" /
"base+body-sha-256" /
token
timestamp = "timestamp" "=" <"> 1*DIGIT <">
CS = OWF "," OWF
4.1. The 'class' Attribute
The name of the token class supported by the server. Servers MAY
support multiple classes per protected resource by providing multiple
challenges, each with a different class.
4.2. The 'method' Attribute
The list of authentication method names supported by the server,
provided as a space-delimited list. Authentication methods are
described in Section 7.
4.3. The 'coverage' Attribute
The list of authentication coverage names supported by the server,
provided as a space-delimited list. If omitted, the attribute
defaults to "base". Authentication coverage is described in
Section 8.
Hammer-Lahav Expires June 10, 2010 [Page 9]
Internet-Draft Token Authentication December 2009
4.4. The 'timestamp' Attribute
Signature-based and hash-based authentication methods use timestamps
in combination with unique nonce values to protect against replay
attacks when used over an unsecure channel.
The timestamp attribute is used by the server to publish its current
time, enabling clients to synchronize their close with the server.
The timestamp value is the current time expressed in the number of
seconds since January 1, 1970 00:00:00 GMT, and MUST be a positive
integer.
To avoid the need to retain an infinite number of nonce values for
future checks, servers MAY choose to restrict the time period after
which a request with an old timestamp is rejected. Servers applying
such a restriction SHOULD provide their current time to the client
either in every challenge or when a request fails due to a timestamp
outside the allowed window.
5. The Authorization Request Header
A client making a request for a protected resource either directly,
or in retrying a request after receiving a 401 status code
(Unauthorized) with a token challenge, MUST include at least one
"Authorization" header field including token scheme credentials.
The "Authorization" header field uses the framework defined by
[RFC2617] as follows:
credentials = "Token" RWS token-response
token-response = token-id
CS class
CS method
[ CS coverage ]
[ CS nonce ]
[ CS timestamp ]
[ CS auth ]
token-id = "token" "=" <"> token <">
method = "method" "=" <"> method-name <">
coverage = "coverage" "=" <"> coverage-name <">
nonce = "nonce" "=" <"> token <">
auth = "auth" "=" <"> token <">
Hammer-Lahav Expires June 10, 2010 [Page 10]
Internet-Draft Token Authentication December 2009
5.1. The 'token' Attribute
The value used to identify the set of token credentials used by the
client to authenticate. The token identifier can be an opaque string
or use a well-defined internal structure, which is determined by the
token class.
5.2. The 'class' Attribute
The name of the token class used by the client to make the request.
5.3. The 'method' Attribute
The name of the authentication method used by the client to make the
request.
5.4. The 'coverage' Attribute
The name of the authentication coverage method used by the client to
make the request. If the attribute is omitted, its value defaults to
"base".
5.5. The 'nonce' Attribute
A random string, uniquely generated by the client to allow the server
to verify that a request has never been made before and helps prevent
replay attacks when requests are made over a non-secure channel. The
nonce value MUST be unique across all requests with the same
timestamp and token combinations.
5.6. The 'timestamp' Attribute
The timestamp value is the current time expressed in the number of
seconds since January 1, 1970 00:00:00 GMT, and MUST be a positive
integer.
5.7. The 'auth' Attribute
The output of the authentication method function after applying it to
the selected coverage as described in Section 7.
6. The Authentication-Error Response Header
A server receiving a request for a protected resource with an invalid
Authorization header field (Section 5) MAY includes the
"Authentication-Error" header field providing the client with
information to help it successfully authenticate with the server.
Hammer-Lahav Expires June 10, 2010 [Page 11]
Internet-Draft Token Authentication December 2009
The "Authentication-Error" header field is defined as follows:
Authentication-Error = "Authentication-Error" ":"
OWS #1error-param
error-param = error-code /
error-info /
error-message /
auth-param
error-code = "error-code" "=" <"> token <">
error-info = "error-info" "=" <"> token <">
error-message = "error-message" "=" quoted-string
6.1. The 'error-code' attribute
6.2. The 'error-info' attribute
6.3. The 'error-message' attribute
7. Authentication Methods
In order for the server to verify the authenticity of the request and
prevent unauthorized access, the client must prove it is the rightful
owner of the credentials. This is accomplished using the
authentication method associated with the token.
This specification provides three methods for the client to prove its
rightful ownership of the credentials: "hmac-sha-1", "hmac-sha-256",
and "rsassa-pkcs1-v1.5-sha-256". In addition, the "none" method is
defined to allow the use of bearer token which does not utilizes any
cryptographic means.
The authentication process does not change the request or its
parameters, with the exception of the "auth" attribute.
7.1. The 'none' Method
The "none" method does not employ a cryptographic algorithm and does
not provide any security on its own. Servers utilizing this method
use the token identifier as a bearer token, relying solely on the
value of the token identifier to authenticate the client.
The "nonce", "timestamp", and "auth" attributes are not used, and
SHOULD NOT be included in authenticated requests. The "coverage"
attribute MUST be set to "none" but MAY be omitted from the request.
Hammer-Lahav Expires June 10, 2010 [Page 12]
Internet-Draft Token Authentication December 2009
Nevertheless, these attributes MUST be included in the normalized
request string together with any other authentication attributes.
7.2. The 'hmac-sha-1' Method
The "hmac-sha-1" authentication method uses the HMAC-SHA1 algorithm
as defined in [RFC2104]:
digest = HMAC-SHA1 (key, text)
The HMAC-SHA1 function variables are used in following way:
text
is set to the value of the normalize request string as
described in Section 8.
key
is set to the shared-secret associated with the token.
digest
is used to set the value of the "auth" attribute, after the
result octet string is base64-encoded per [RFC2045] section
6.8.
7.3. The 'hmac-sha-256' Method
The "hmac-sha-256" authentication method uses the HMAC algorithm as
defined in [RFC2104] together with the SHA-256 hash function defined
in [NIST FIPS-180-3]:
digest = HMAC-SHA256 (key, text)
The HMAC-SHA256 function variables are used in following way:
text
is set to the value of the normalize request string as
described in Section 8.
key
is set to the shared-secret associated with the token.
digest
is used to set the value of the "auth" attribute, after the
result octet string is base64-encoded per [RFC2045] section
6.8.
Hammer-Lahav Expires June 10, 2010 [Page 13]
Internet-Draft Token Authentication December 2009
7.4. The 'rsassa-pkcs1-v1.5-sha-256' Method
The "rsassa-pkcs1-v1.5-sha-256" signature method uses the RSASSA-
PKCS1-v1_5 signature algorithm as defined in [RFC3447] section 8.2
(also known as PKCS#1), using SHA-256 as the hash function as defined
in [NIST FIPS-180-3] for EMSA-PKCS1-v1_5.
The normalized request string is signed using the RSA private key
associated with the token as defined in [RFC3447] section 8.2.1:
S = RSASSA-PKCS1-V1_5-SIGN (K, M)
Where:
K
is set to the RSA private key associated with the token,
M
is set to the value of the normalized request string described
in Section 8, and
S
is the result signature used to set the value of the "auth"
attribute, after the result octet string is base64-encoded per
[RFC2045] section 6.8.
The server verifies the signature per [RFC3447] section 8.2.2:
RSASSA-PKCS1-V1_5-VERIFY ((n, e), M, S)
Where:
(n, e)
is set to the RSA public key associated with the token,
M
is set to the value of the normalized request string described
in Section 8, and
S
is set to the octet string value of the "auth" attribute
received from the client.
Hammer-Lahav Expires June 10, 2010 [Page 14]
Internet-Draft Token Authentication December 2009
8. Coverage Methods
The normalized request string is a consistent, reproducible
concatenation of several of the HTTP request elements into a single
string. The string is used as an input to the authentication methods
with the exception of "none".
8.1. The 'base' Method
When using the "base" method, the normalized request string includes
the following components of the HTTP request:
o The HTTP request method (e.g. "GET", "POST", etc.).
o The authority as declared by the HTTP "Host" request header.
o The request resource URI.
o The Authorization header field (Section 5) attributes, with the
exception of the "auth" attribute.
The "base" normalized request string does not cover the entire HTTP
request. Most notably, it does not include the entity-body or most
HTTP entity-headers. It is important to note that the server cannot
verify the authenticity of the excluded request elements without
using additional protections such as SSL/TLS or other methods.
8.1.1. String Construction
The normalized request string is constructed by concatenating
together, in order, the following HTTP request elements:
1. The HTTP request method in uppercase. For example: "HEAD",
"GET", "POST", etc.
2. A "," character (ASCII code 44).
3. The hostname, colon-separated (ASCII code 58) from the TCP port
used to make the request as included in the HTTP request "Host"
header field. The port MUST be included even if it is not
included in the "Host" header field (i.e. the default port for
the scheme).
4. A "," character (ASCII code 44).
5. Any authentication attribute, with the exception of the "auth",
which is assigned a value (including default values), are added
to the normalized request string as follows:
Hammer-Lahav Expires June 10, 2010 [Page 15]
Internet-Draft Token Authentication December 2009
1. The name of each parameter is concatenated to its
corresponding value using an "=" character (ASCII code 61) as
separator, even if the value is empty.
2. The name/value pairs are sorted using ascending byte value
ordering.
3. The sorted name/value pairs are concatenated together into a
single string by using a "," character (ASCII code 44) as
separator.
6. A "," character (ASCII code 44).
7. The request resource URI.
8.2. The 'base+body-hmac-sha-256' Method
The "base+body-hmac-sha-256" method added the request entity-body to
the elements included in the normalized request string. It does not
include the entity-body directly in the normalized string. Instead,
it calculates the hash value of the entity-body using the SHA-256
hash function defined in [NIST FIPS-180-3].
The normalized request string is constructed following the same
process defined in Section 8.1.1, with the following addition:
o Before constructing the string, the entity-body hash is calculated
by applying the SHA-256 hash function on the raw entity-body
content.
o The hash value is added to the list of authentication attributes
by assigning its value to the "body-hash" attribute name. This is
done prior to the attributes being sorted and added to the string.
o The "body-hash" attribute is only included in the normalized
request string and is not added to the Authorization header field
(Section 5).
9. Scheme Extensions
10. Security Considerations
As stated in [RFC2617], the greatest sources of risks are usually
found not in the core protocol itself but in policies and procedures
surrounding its use. Implementers are strongly encouraged to assess
how this protocol addresses their security requirements.
Hammer-Lahav Expires June 10, 2010 [Page 16]
Internet-Draft Token Authentication December 2009
10.1. Credentials Transmission
This specification does not describe any mechanism for obtaining or
transmitting raw tokens credentials. Methods used to obtain tokens
should ensure that these transmissions are protected using transport-
layer mechanisms such as TLS or SSL.
10.2. Confidentiality of Requests
While this protocol provides a mechanism for verifying the integrity
of requests, it provides no guarantee of request confidentiality.
Unless further precautions are taken, eavesdroppers will have full
access to request content. Servers should carefully consider the
kinds of data likely to be sent as part of such requests, and should
employ transport-layer security mechanisms to protect sensitive
resources.
10.3. Spoofing by Counterfeit Servers
This protocol makes no attempt to verify the authenticity of the
server. A hostile party could take advantage of this by intercepting
the client's requests and returning misleading or otherwise incorrect
responses. Service providers should consider such attacks when
developing services using this protocol, and should require
transport-layer security for any requests where the authenticity of
the server or of request responses is an issue.
10.4. Plaintext Storage of Credentials
When used with a symmetric shared-secret authentication method, the
token shared-secret function the same way passwords do in traditional
authentication systems. In order to compute the signatures used in
methods, the server must have access to these secrets in plaintext
form. This is in contrast, for example, to modern operating systems,
which store only a one-way hash of user credentials.
If an attacker were to gain access to these secrets - or worse, to
the server's database of all such secrets - he or she would be able
to perform any action on behalf of any resource owner. Accordingly,
it is critical that servers protect these secrets from unauthorized
access.
10.5. Scoping of Access Requests
By itself, this protocol does not provide any method for scoping the
access rights granted to a client. However, most applications do
require greater granularity of access rights. For example, servers
may wish to make it possible to grant access to some protected
Hammer-Lahav Expires June 10, 2010 [Page 17]
Internet-Draft Token Authentication December 2009
resources but not others, or to grant only limited access (such as
read-only access) to those protected resources.
When implementing this protocol, servers should consider the types of
access resource owners may wish to grant clients, and should provide
mechanisms to do so. Servers should also take care to ensure that
resource owners understand the access they are granting, as well as
any risks that may be involved.
10.6. Entropy of Secrets
Unless a transport-layer security protocol is used, eavesdroppers
will have full access to authenticated requests and signatures, and
will thus be able to mount offline brute-force attacks to recover the
credentials used. Servers should be careful to assign shared-secrets
which are long enough, and random enough, to resist such attacks for
at least the length of time that the shared-secrets are valid.
For example, if shared-secrets are valid for two weeks, servers
should ensure that it is not possible to mount a brute force attack
that recovers the shared-secret in less than two weeks. Of course,
servers are urged to err on the side of caution, and use the longest
secrets reasonable.
It is equally important that the pseudo-random number generator
(PRNG) used to generate these secrets be of sufficiently high
quality. Many PRNG implementations generate number sequences that
may appear to be random, but which nevertheless exhibit patterns or
other weaknesses which make cryptanalysis or brute force attacks
easier. Implementers should be careful to use cryptographically
secure PRNGs to avoid these problems.
10.7. Denial of Service / Resource Exhaustion Attacks
This specification includes a number of features which may make
resource exhaustion attacks against servers possible. For example,
this protocol requires servers to track used nonces. If an attacker
is able to use many nonces quickly, the resources required to track
them may exhaust available capacity. And again, this protocol can
require servers to perform potentially expensive computations in
order to verify the signature on incoming requests. An attacker may
exploit this to perform a denial of service attack by sending a large
number of invalid requests to the server.
Resource Exhaustion attacks are by no means specific to this
specification. However, implementers should be careful to consider
the additional avenues of attack that this protocol exposes, and
design their implementations accordingly. For example, entropy
Hammer-Lahav Expires June 10, 2010 [Page 18]
Internet-Draft Token Authentication December 2009
starvation typically results in either a complete denial of service
while the system waits for new entropy or else in weak (easily
guessable) secrets. When implementing this protocol, servers should
consider which of these presents a more serious risk for their
application and design accordingly.
10.8. Coverage Limitations
The normalized request string has been designed to support the
authentication methods defined in this specification. Those
designing additional methods, should evaluated the compatibility of
the normalized request string with their security requirements.
Since the normalized request string does not cover the entire HTTP
request, servers should employ additional mechanisms to protect such
elements.
11. IANA Considerations
12. Acknowledgments
The author would like to thank Richard Barnes, Breno de Medeiros,
Brian Eaton, Ben Laurie, Mark Nottingham, John Panzer, and Peter
Saint-Andre for their suggestions, feedback, and continued support.
Appendix A. Document History
[[ To be removed by the RFC editor before publication as an RFC. ]]
-00
o Initial (incomplete) draft.
13. References
13.1. Normative References
[I-D.ietf-httpbis-p1-messaging]
Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P., Berners-Lee, T., and J. Reschke,
"HTTP/1.1, part 1: URIs, Connections, and Message
Parsing", draft-ietf-httpbis-p1-messaging-08 (work in
progress), October 2009.
[NIST FIPS-180-3]
Hammer-Lahav Expires June 10, 2010 [Page 19]
Internet-Draft Token Authentication December 2009
National Institute of Standards and Technology, "Secure
Hash Standard (SHS). FIPS PUB 180-3, October 2008".
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
13.2. Informative References
[I-D.ietf-oauth-web-delegation]
Hammer-Lahav, E., "The OAuth Protocol: Web Delegation",
draft-ietf-oauth-web-delegation-01 (work in progress),
July 2009.
URIs
[1] <https://www.ietf.org/mailman/listinfo/oauth>
Author's Address
Eran Hammer-Lahav
Yahoo!
Email: eran@hueniverse.com
URI: http://hueniverse.com
Hammer-Lahav Expires June 10, 2010 [Page 20]
| PAFTECH AB 2003-2026 | 2026-04-24 12:11:40 |