One document matched: draft-jones-json-web-signature-00.xml
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<rfc category="std" docName="draft-jones-json-web-signature-00"
ipr="trust200902">
<front>
<title>JSON Web Signature (JWS)</title>
<author fullname="Michael B. Jones" initials="M.B." surname="Jones">
<organization>Microsoft</organization>
<address>
<email>mbj@microsoft.com</email>
<uri>http://self-issued.info/</uri>
</address>
</author>
<author fullname="Dirk Balfanz" initials="D." surname="Balfanz">
<organization>Google</organization>
<address>
<email>balfanz@google.com</email>
</address>
</author>
<author fullname="John Bradley" initials="J." surname="Bradley">
<organization>independent</organization>
<address>
<email>ve7jtb@ve7jtb.com</email>
</address>
</author>
<author fullname="Yaron Y. Goland" initials="Y.Y." surname="Goland">
<organization>Microsoft</organization>
<address>
<email>yarong@microsoft.com</email>
</address>
</author>
<author fullname="John Panzer" initials="J." surname="Panzer">
<organization>Google</organization>
<address>
<email>jpanzer@google.com</email>
</address>
</author>
<author fullname="Nat Sakimura" initials="N." surname="Sakimura">
<organization>Nomura Research Institute</organization>
<address>
<email>n-sakimura@nri.co.jp</email>
</address>
</author>
<author fullname="Paul Tarjan" initials="P." surname="Tarjan">
<organization>Facebook</organization>
<address>
<email>pt@fb.com</email>
</address>
</author>
<date day="28" month="March" year="2011" />
<area>Applications</area>
<keyword>RFC</keyword>
<keyword>Request for Comments</keyword>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<keyword>Assertion</keyword>
<keyword>Simple Web Token</keyword>
<keyword>Security Token</keyword>
<keyword>SWT</keyword>
<keyword>JavaScript Object Notation</keyword>
<keyword>JSON</keyword>
<keyword>JSON Web Token</keyword>
<keyword>JWT</keyword>
<keyword>JSON Web Signature</keyword>
<keyword>JWS</keyword>
<keyword>JSON Web Encryption</keyword>
<keyword>JWE</keyword>
<abstract>
<t>
JSON Web Signature (JWS) is a means of representing signed
content using JSON data structures. Related encryption
capabilities are described in the separate JSON Web Encryption
(JWE) specification.
</t>
</abstract>
<note title="Requirements Language">
<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 <xref target="RFC2119">RFC 2119</xref>.
</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>
JSON Web Signature (JWS) is a compact signature format
intended for space constrained environments such as HTTP
Authorization headers and URI query parameters. The JWS
signature mechanisms are independent of the type of content
being signed, allowing arbitrary content to be signed. A
related encryption capability is described in a separate JSON
Web Encryption (JWE) <xref target="JWE" /> specification.
</t>
</section>
<section title="Terminology">
<t>
<list style="hanging">
<t hangText="JSON Web Signature (JWS)">
A data structure cryptographically securing a JWS Header
Input and a JWS Payload Input with a JWS Crypto Output.
</t>
<t hangText="JWS Header Input">
A string containing a base64url encoded JSON object that
describes the cryptographic operations applied to the JWS
Header Input and the JWS Payload Input.
</t>
<t hangText="JWS Payload Input">
A string containing base64url encoded content.
</t>
<t hangText="JWS Crypto Output">
A string containing base64url encoded cryptographic
material that secures the contents of the JWS Header Input
and the JWS Payload Input.
</t>
<t hangText="Decoded JWS Header Input">
JWS Header Input that has been base64url decoded back into
a JSON object.
</t>
<t hangText="Decoded JWS Payload Input">
JWS Payload Input that has been base64url decoded.
</t>
<t hangText="Decoded JWS Crypto Output">
JWS Crypto Output that has been base64url decoded back
into cryptographic material.
</t>
<t hangText="JWS Signing Input">
The concatenation of the JWS Header Input, a period ('.')
character, and the JWS Payload Input.
</t>
<t hangText="Header Parameter Names">
The names of the members within the JSON object
represented in a JWS Header Input.
</t>
<t hangText="Header Parameter Values">
The values of the members within the JSON object
represented in a JWS Header Input.
</t>
<t hangText="Digital Signature">
For the purposes of this specification, we use this term
to encompass both Hash-based Message Authentication Codes
(HMACs), which can provide authenticity but not
non-repudiation, and digital signatures using public key
algorithms, which can provide both. Readers should be
aware of this distinction, despite the decision to use a
single term for both concepts to improve readability of
the specification.
</t>
<t hangText="Base64url Encoding">
For the purposes of this specification, this term always
refers to the he URL- and filename-safe Base64 encoding
described in <xref target="RFC4648">RFC 4648</xref>,
Section 5, with the '=' padding characters omitted, as
permitted by Section 3.2.
</t>
</list>
</t>
</section>
<section title="JSON Web Signature (JWS) Overview">
<t>
JWSs represent content that is base64url encoded and digitally
signed, and optionally encrypted, using JSON data structures.
A portion of the base64url encoded content that is signed is
the JWS Payload Input.
</t>
<t>
An accompanying base64url encoded JSON object - the JWS Header
Input - describes the signature method used.
</t>
<t>
The names within the header JSON object MUST be unique. These
names are referred to as Header Parameter Names. The
corresponding values are referred to as Header Parameter
Values.
</t>
<t>
JWSs contain a signature that ensures the integrity of the
contents of the JWS Header Input and the JWS Payload Input.
This signature value is the JWS Crypto Output. The JSON
Header object MUST contain an "alg" parameter, the value of
which is a string that unambiguously identifies the algorithm
used to sign the JWS Header Input and the JWS Payload Input to
produce the JWS Crypto Output.
</t>
<section title="Example JWS" anchor="ExampleJWS">
<t>
The following example JSON header object declares that the
encoded object is a JSON Web Token (JWT) <xref target="JWT" />
and the JWS Header Input and the JWS Payload Input are
signed using the HMAC SHA-256 algorithm:
</t>
<artwork><![CDATA[{"typ":"JWT",
"alg":"HS256"}]]></artwork>
<t>
Base64url encoding the UTF-8 representation of the JSON
header object yields this JWS Header Input value:
</t>
<artwork><![CDATA[eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9]]></artwork>
<t>
The following is an example of a JSON object that can be
encoded to produce a JWS Payload Input. (Note that
the payload can be any base64url encoded content, and need
not be a base64url encoded JSON object.)
</t>
<artwork><![CDATA[{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}]]></artwork>
<t>
Base64url encoding the UTF-8 representation of the JSON
object yields the following JWS Payload Input.
</t>
<artwork><![CDATA[eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ]]></artwork>
<t>
Signing the UTF-8 representation of the JWS Signing Input
(the concatenation of the JWS Header Input, a period ('.')
character, and the JWS Payload Input) with the HMAC
SHA-256 algorithm and base64url encoding the result, as per
<xref target="SigningWithHMACSHA256"></xref>, yields this
JWS Crypto Output value:
</t>
<artwork><![CDATA[dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk]]></artwork>
<t>
This computation is illustrated in more detail in <xref
target="HMACSHA256Example"></xref>.
</t>
</section>
</section>
<section title="JWS Header">
<t>
The members of the JSON object represented by the Decoded JWS
Header Input describe the signature applied to the JWS
Header Input and the JWS Payload Input and optionally
additional properties of the JWS. Implementations MUST
understand the entire contents of the header; otherwise, the
JWS MUST be rejected for processing.
</t>
<section title="Reserved Header Parameter Names" anchor="ReservedHeaderParameterName">
<t>
The following header parameter names are reserved. All
the names are short because a core goal of JWSs is for the
representations to be compact.
</t>
<texttable title="Reserved Header Parameter Definitions" anchor="HeaderParameterTable">
<ttcol align="left">Header Parameter Name</ttcol>
<ttcol align="left">JSON Value Type</ttcol>
<ttcol align="left">Header Parameter Syntax</ttcol>
<ttcol align="left">Header Parameter Semantics</ttcol>
<c>alg</c>
<c>string</c>
<c>StringAndURI</c>
<c>
The <spanx style="verb">alg</spanx> (algorithm) header parameter identifies the
cryptographic algorithm used to secure the JWS. A list of
reserved alg values is in <xref target="AlgTable"></xref>.
The processing of the <spanx style="verb">alg</spanx> (algorithm) header
parameter, if present, requires that the value of the
<spanx style="verb">alg</spanx> header parameter MUST be one that is both
supported and for which there exists a key for use with
that algorithm associated with the signer of the content.
This header parameter is REQUIRED.
</c>
<c>typ</c>
<c>string</c>
<c>String</c>
<c>
The <spanx style="verb">typ</spanx> (type) header parameter is used to declare the
type of the signed content.
This header parameter is OPTIONAL.
</c>
<c>jku</c>
<c>string</c>
<c>URL</c>
<c>
The <spanx style="verb">jku</spanx> (JSON Key URL) header parameter is a URL that
points to JSON-encoded public key certificates that can be
used to validate the signature. The specification for
this encoding is TBD. This header parameter is OPTIONAL.
</c>
<c>kid</c>
<c>string</c>
<c>String</c>
<c>
The <spanx style="verb">kid</spanx> (key ID) header parameter is a hint indicating
which specific key owned by the signer should be used to
validate the signature. This allows signers to explicitly
signal a change of key to recipients. Omitting this
parameter is equivalent to setting it to an empty string.
The interpretation of the contents of the <spanx style="verb">kid</spanx> parameter
is unspecified. This header parameter is OPTIONAL.
</c>
<c>x5u</c>
<c>string</c>
<c>URL</c>
<c>
The <spanx style="verb">x5u</spanx> (X.509 URL) header parameter is a URL that
points to an X.509 public key certificate that can be used
to validate the signature. This certificate MUST conform
to <xref target="RFC5280">RFC 5280</xref>. This header
parameter is OPTIONAL.
</c>
<c>x5t</c>
<c>string</c>
<c>String</c>
<c>
The <spanx style="verb">x5t</spanx> (x.509 certificate thumbprint) header parameter
provides a base64url encoded SHA-256 thumbprint
(a.k.a. digest) of the DER encoding of an X.509
certificate that can be used to match a certificate. This
header parameter is OPTIONAL.
</c>
</texttable>
<t>
Additional reserved header parameter names MAY be defined
via the IANA JSON Web Signature Header Parameters registry,
as per <xref target="IANA" />. The syntax values used above
are defined as follows:
</t>
<texttable title="Header Parameter Syntax Definitions" anchor="SyntaxDefinitions">
<ttcol align="left">Syntax Name</ttcol>
<ttcol align="left">Syntax Definition</ttcol>
<c>IntDate</c>
<c>
The number of seconds from 1970-01-01T0:0:0Z as measured
in UTC until the desired date/time. See <xref
target="RFC3339">RFC 3339</xref> for details regarding
date/times in general and UTC in particular.
</c>
<c>String</c>
<c>
Any string value MAY be used.
</c>
<c>StringAndURI</c>
<c>
Any string value MAY be used but a value containing a ":"
character MUST be a URI as defined in <xref
target="RFC3986">RFC 3986</xref>.
</c>
<c>URL</c>
<c>
A URL as defined in <xref target="RFC1738">RFC 1738</xref>.
</c>
</texttable>
</section>
<section title="Public Header Parameter Names" anchor="PublicHeaderParameterName">
<t>
Additional header parameter names can be defined by those
using JWSs. However, in order to prevent collisions, any new
header parameter name or algorithm value SHOULD either be
defined in the IANA JSON Web Signature Header Parameters
registry or be defined as a URI that contains a collision
resistant namespace. In each case, the definer of the name
or value MUST take reasonable precautions to make sure they
are in control of the part of the namespace they use to
define the header parameter name.
</t>
<t>
New header parameters should be introduced sparingly, as
they can result in non-interoperable JWSs.
</t>
</section>
<section title="Private Header Parameter Names" anchor="PrivateHeaderParameterName">
<t>
A producer and consumer of a JWS may agree to any header
parameter name that is not a Reserved Name <xref
target="ReservedHeaderParameterName"></xref> or a Public
Name <xref
target="PublicHeaderParameterName"></xref>. Unlike Public
Names, these private names are subject to collision and
should be used with caution.
</t>
<t>
New header parameters should be introduced sparingly, as
they can result in non-interoperable JWSs.
</t>
</section>
</section>
<section title="Rules for Creating and Validating a JWS">
<t>
To create a JWS, one MUST follow these steps:
<list style="numbers">
<t>
Create the payload content to be encoded as the Decoded
JWS Payload Input.
</t>
<t>
Base64url encode the Decoded JWS Payload Input. This
encoding becomes the JWS Payload Input.
</t>
<t>
Create a JSON object containing a set of desired header
parameters. Note that white space is explicitly allowed
in the representation and no canonicalization is performed
before encoding.
</t>
<t>
Translate this JSON object's Unicode code points into
UTF-8, as defined in <xref target="RFC3629">RFC
3629</xref>.
</t>
<t>
Base64url encode the UTF-8 representation of this JSON
object as defined in this specification (without
padding). This encoding becomes the JWS Header Input.
</t>
<t>
Compute the JWS Crypto Output in the manner defined for
the particular algorithm being used. The JWS Signing
Input is always the concatenation of the JWS Header Input,
a period ('.') character, and the JWS Payload Input. The
<spanx style="verb">alg</spanx> header parameter MUST be
present in the JSON Header Input, with the algorithm value
accurately representing the algorithm used to construct
the JWS Crypto Input.
</t>
</list>
</t>
<t>
When validating a JWS, the following steps MUST be taken. If
any of the listed steps fails, then the signed content MUST be
rejected.
</t>
<t>
<list style="numbers">
<t>
The JWS Payload Input MUST be successfully base64url
decoded following the restriction given in this specification that
no padding characters have been used.
</t>
<t>
The JWS Header Input MUST be successfully base64url
decoded following the restriction given in this specification that
no padding characters have been used.
</t>
<t>
The Decoded JWS Header Input MUST be completely valid
JSON syntax conforming to <xref target="RFC4627">RFC
4627</xref>.
</t>
<t>
The JWS Crypto Output MUST be successfully base64url
decoded following the restriction given in this specification that
no padding characters have been used.
</t>
<t>
The JWS Header Input MUST be validated to only include
parameters and values whose syntax and semantics are both
understood and supported.
</t>
<t>
The JWS Crypto Output MUST be successfully validated
against the JWS Header Input and JWS Payload Input
in the manner defined for the algorithm being used, which
MUST be accurately represented by the value of the <spanx style="verb">alg</spanx>
header parameter, which MUST be present.
</t>
</list>
</t>
<t>
Processing a JWS inevitably requires comparing known strings
to values in the header. For example, in checking what the
algorithm is, the Unicode string encoding <spanx style="verb">alg</spanx> will be
checked against the member names in the Decoded JWS Header
Input to see if there is a matching header parameter
name. A similar process occurs when determining if the value
of the <spanx style="verb">alg</spanx> header parameter represents a supported
algorithm. Comparing Unicode strings, however, has significant
security implications, as per <xref target="Security"></xref>.
</t>
<t>
Comparisons between JSON strings and other Unicode strings
MUST be performed as specified below:
</t>
<t>
<list style="numbers">
<t>
Remove any JSON applied escaping to produce an array of
Unicode code points.
</t>
<t>
<xref target="USA15">Unicode Normalization</xref> MUST NOT
be applied at any point to either the JSON string or to
the string it is to be compared against.
</t>
<t>
Comparisons between the two strings MUST be performed as a
Unicode code point to code point equality comparison.
</t>
</list>
</t>
</section>
<section title="Base64url encoding as used by JWSs" anchor="base64urllogic">
<t>
JWSs make use of the base64url encoding as defined in <xref
target="RFC4648">RFC 4648</xref>. As allowed by Section 3.2 of
the RFC, this specification mandates that base64url encoding
when used with JWSs MUST NOT use padding. The reason for this
restriction is that the padding character ('=') is not URL
safe.
</t>
<t>
For notes on implementing base64url encoding without padding,
see <xref target="base64urlnotes"></xref>.
</t>
</section>
<section title="Signing JWSs with Cryptographic Algorithms" anchor="Signing">
<t>
JWSs use specific cryptographic algorithms to sign the contents
of the JWS Header Input and the JWS Payload Input. The
use of the following algorithms for producing JWSs is defined in
this section. The table below is the list of <spanx style="verb">alg</spanx> header
parameter values reserved by this specification, each of which
is explained in more detail in the following sections:
</t>
<texttable title="JSON Web Signature Reserved Algorithm Values" anchor="AlgTable">
<ttcol align="left">Alg Parameter Value</ttcol>
<ttcol align="left">Algorithm</ttcol>
<c>HS256</c>
<c>HMAC using SHA-256 hash algorithm</c>
<c>HS384</c>
<c>HMAC using SHA-384 hash algorithm</c>
<c>HS512</c>
<c>HMAC using SHA-512 hash algorithm</c>
<c>RS256</c>
<c>RSA using SHA-256 hash algorithm</c>
<c>RS384</c>
<c>RSA using SHA-384 hash algorithm</c>
<c>RS512</c>
<c>RSA using SHA-512 hash algorithm</c>
<c>ES256</c>
<c>ECDSA using P-256 curve and SHA-256 hash algorithm</c>
<c>ES384</c>
<c>ECDSA using P-384 curve and SHA-384 hash algorithm</c>
<c>ES512</c>
<c>ECDSA using P-521 curve and SHA-512 hash algorithm</c>
</texttable>
<t>
Of these algorithms, only HMAC SHA-256 and RSA SHA-256 MUST be
implemented by conforming implementations. It is RECOMMENDED
that implementations also support the ECDSA P-256 SHA-256
algorithm. Support for other algorithms is OPTIONAL.
</t>
<t>
The signed content for a JWS is the same for all algorithms:
the concatenation of the JWS Header Input, a period ('.')
character, and the JWS Payload Input. This character sequence
is referred to as the JWS Signing Input. Note that if the JWS
represents a JWT, this corresponds to the portion of the JWT
representation preceding the second period character. The
UTF-8 representation of the JWS Signing Input is passed to the
respective signing algorithms.
</t>
<section title="Creating a JWS with HMAC SHA-256" anchor="SigningWithHMACSHA256">
<t>
Hash based Message Authentication Codes (HMACs) enable one to
use a secret plus a cryptographic hash function to generate a
Message Authentication Code (MAC). This can be used to
demonstrate that the MAC matches the hashed content, in this
case the JWS Signing Input, which therefore demonstrates that
whoever generated the MAC was in possession of the secret.
</t>
<t>
The algorithm for implementing and validating HMACs is
provided in <xref target="RFC2104">RFC 2104</xref>. Although
any HMAC can be used with JWSs, this section defines the use
of the SHA-256 cryptographic hash function as defined in <xref
target="FIPS.180-3">FIPS 180-3</xref>. The reserved <spanx style="verb">alg</spanx>
header parameter value <spanx style="verb">HS256</spanx> is used in the JWS Header
Input to indicate that the JWS Crypto Output contains a
base64url encoded HMAC SHA-256 HMAC value.
</t>
<t>
The HMAC SHA-256 MAC is generated as follows:
<list style="numbers">
<t>
Apply the HMAC SHA-256 algorithm to the UTF-8
representation of the JWS Signing Input using the shared
key to produce an HMAC.
</t>
<t>
Base64url encode the HMAC as defined in this document.
</t>
</list>
The output is the JWS Crypto Output for that JWS.
</t>
<t>
The HMAC SHA-256 MAC for a JWS is validated as follows:
<list style="numbers">
<t>
Apply the HMAC SHA-256 algorithm to the UTF-8
representation of the JWS Signing Input of the JWS using
the shared key.
</t>
<t>
Base64url encode the previously generated HMAC as defined
in this document.
</t>
<t>
If the JWS Crypto Output and the previously calculated
value exactly match, then one has confirmation that the
key was used to generate the HMAC on the JWS and that the
contents of the JWS have not be tampered with.
</t>
<t>
If the validation fails, the signed content MUST be rejected.
</t>
</list>
</t>
<t>
Signing with the HMAC SHA-384 and HMAC SHA-512 algorithms is
performed identically to the procedure for HMAC SHA-256 - just
with correspondingly longer key and result values.
</t>
</section>
<section title="Creating a JWS with RSA SHA-256" anchor="DefiningRSA">
<t>
This section defines the use of the RSASSA-PKCS1-v1_5
signature algorithm as defined in <xref target="RFC3447">RFC
3447</xref>, Section 8.2 (commonly known as PKCS#1), using
SHA-256 as the hash function. Note that the use of the
RSASSA-PKCS1-v1_5 algorithm is described in <xref
target="FIPS.186-3">FIPS 186-3</xref>, Section 5.5, as is the
SHA-256 cryptographic hash function, which is defined in <xref
target="FIPS.180-3">FIPS 180-3</xref>. The reserved <spanx style="verb">alg</spanx>
header parameter value <spanx style="verb">RS256</spanx> is used in the JWS Header
Input to indicate that the JWS Crypto Output contains an
RSA SHA-256 signature.
</t>
<t>
A 2048-bit or longer key length MUST be used with this
algorithm.
</t>
<t>
The RSA SHA-256 signature is generated as follows:
<list style="numbers">
<t>
Let K be the signer's RSA private key and let M be the
UTF-8 representation of the JWS Signing Input.
</t>
<t>
Compute the octet string S = RSASSA-PKCS1-V1_5-SIGN (K,
M) using SHA-256 as the hash function.
</t>
<t>
Base64url encode the octet string S, as defined in this
document.
</t>
</list>
The output is the JWS Crypto Output for that JWS.
</t>
<t>
The RSA SHA-256 signature for a JWS is validated as follows:
<list style="numbers">
<t>
Take the JWS Crypto Output and base64url decode it into
an octet string S. If decoding fails, then the signed content MUST
be rejected.
</t>
<t>
Let M be the UTF-8 representation of the JWS Signing
Input and let (n, e) be the public key corresponding to
the private key used by the signer.
</t>
<t>
Validate the signature with RSASSA-PKCS1-V1_5-VERIFY ((n,
e), M, S) using SHA-256 as the hash function.
</t>
<t>
If the validation fails, the signed content MUST be rejected.
</t>
</list>
</t>
<t>
Signing with the RSA SHA-384 and RSA SHA-512 algorithms is
performed identically to the procedure for RSA SHA-256 - just
with correspondingly longer key and result values.
</t>
</section>
<section title="Creating a JWS with ECDSA P-256 SHA-256" anchor="DefiningECDSA">
<t>
The Elliptic Curve Digital Signature Algorithm (ECDSA) is
defined by <xref target="FIPS.186-3">FIPS 186-3</xref>. ECDSA
provides for the use of Elliptic Curve cryptography, which is
able to provide equivalent security to RSA cryptography but
using shorter key lengths and with greater processing
speed. This means that ECDSA signatures will be substantially
smaller in terms of length than equivalently strong RSA
Digital Signatures.
</t>
<t>
This specification defines the use of ECDSA with the P-256
curve and the SHA-256 cryptographic hash function. The P-256
curve is also defined in FIPS 186-3. The reserved <spanx style="verb">alg</spanx>
header parameter value <spanx style="verb">ES256</spanx> is used in the JWS Header
Input to indicate that the JWS Crypto Output contains an
ECDSA P-256 SHA-256 signature.
</t>
<t>
A JWS is signed with an ECDSA P-256 SHA-256 signature as
follows:
<list style="numbers">
<t>
Generate a digital signature of the UTF-8 representation
of the JWS Signing Input using ECDSA P-256 SHA-256 with
the desired private key. The output will be the EC point
(R, S), where R and S are unsigned integers.
</t>
<t>
Turn R and S into byte arrays in big endian order. Each
array will be 32 bytes long.
</t>
<t>
Concatenate the two byte arrays in the order R and then S.
</t>
<t>
Base64url encode the 64 byte array as defined in this
specification.
</t>
</list>
The output is the JWS Crypto Output for the JWS.
</t>
<t>
The ECDSA P-256 SHA-256 signature for a JWS is validated as follows:
<list style="numbers">
<t>
Take the JWS Crypto Output and base64url decode it into a
byte array. If decoding fails, the signed content MUST be rejected.
</t>
<t>
The output of the base64url decoding MUST be a 64 byte
array.
</t>
<t>
Split the 64 byte array into two 32 byte arrays. The first
array will be R and the second S. Remember that the byte
arrays are in big endian byte order; please check the
ECDSA validator in use to see what byte order it requires.
</t>
<t>
Submit the UTF-8 representation of the JWS Signing
Input, R, S and the public key (x, y) to the ECDSA P-256
SHA-256 validator.
</t>
<t>
If the validation fails, the signed content MUST be rejected.
</t>
</list>
The ECDSA validator will then determine if the digital
signature is valid, given the inputs. Note that ECDSA digital
signature contains a value referred to as K, which is a random
number generated for each digital signature instance. This
means that two ECDSA digital signatures using exactly the same
input parameters will output different signatures because
their K values will be different. The consequence of this is
that one must validate an ECDSA signature by submitting the
previously specified inputs to an ECDSA validator.
</t>
<t>
Signing with the ECDSA P-384 SHA-384 and ECDSA P-521 SHA-512
algorithms is performed identically to the procedure for ECDSA
P-256 SHA-256 - just with correspondingly longer key and
result values.
</t>
</section>
<section title="Additional Algorithms" anchor="MoreAlgs">
<t>
Additional algorithms MAY be used to protect JWSs with
corresponding <spanx style="verb">alg</spanx> header parameter values being defined to
refer to them. New <spanx style="verb">alg</spanx> header parameter values SHOULD
either be defined in the IANA JSON Web Signature Algorithms
registry or be a URI that contains a collision resistant
namespace. In particular, the use of algorithm identifiers
defined in <xref target="RFC3275">XML DSIG</xref> and
related specifications is permitted.
</t>
</section>
</section>
<section title="IANA Considerations" anchor="IANA">
<t>
This specification calls for:
<list style="symbols">
<t>
A new IANA registry entitled "JSON Web Signature Header
Parameters" for reserved header parameter names is defined
in <xref target="ReservedHeaderParameterName"></xref>.
Inclusion in the registry is RFC Required in the <xref
target="RFC5226">RFC 5226</xref> sense for reserved JWS
header parameter names that are intended to be
interoperable between implementations. The registry will
just record the reserved header parameter name and a
pointer to the RFC that defines it. This specification
defines inclusion of the header parameter names defined in
<xref target="HeaderParameterTable"></xref>.
</t>
<t>
A new IANA registry entitled "JSON Web Signature Algorithms"
for reserved values used with the <spanx style="verb">alg</spanx> header parameter
values is defined in <xref target="MoreAlgs"></xref>. Inclusion
in the registry is RFC Required in the <xref
target="RFC5226">RFC 5226</xref> sense. The registry will
just record the <spanx style="verb">alg</spanx> value and a pointer to the RFC that
defines it. This specification defines inclusion of the
algorithm values defined in <xref
target="AlgTable"></xref>.
</t>
</list>
</t>
</section>
<section title="Security Considerations" anchor="Security">
<t>
TBD: Lots of work to do here. We need to remember to look into
any issues relating to security and JSON parsing. One wonders
just how secure most JSON parsing libraries are. Were they
ever hardened for security scenarios? If not, what kind of
holes does that open up? Also, we need to walk through the
JSON standard and see what kind of issues we have especially
around comparison of names. For instance, comparisons of
header parameter names and other parameters must occur after
they are unescaped. Need to also put in text about: Importance
of keeping secrets secret. Rotating keys. Strengths and
weaknesses of the different algorithms.
</t>
<t>
TBD: Need to put in text about why strict JSON validation is
necessary. Basically, that if malformed JSON is received then
the intent of the sender is impossible to reliably discern.
</t>
<section title="Unicode Comparison Security Issues">
<t>
Header parameter names in JWSs are Unicode strings. For
security reasons, the representations of these names must be
compared verbatim after performing any escape processing (as
per <xref target="RFC4627">RFC 4627</xref>, Section 2.5).
</t>
<t>
This means, for instance, that these JSON strings must
compare as being equal ("sig", "\u0073ig"), whereas these
must all compare as being not equal to the first set or to
each other ("SIG", "Sig", "si\u0047").
</t>
<t>
JSON strings MAY contain characters outside the Unicode
Basic Multilingual Plane. For instance, the G clef
character (U+1D11E) may be represented in a JSON string as
"\uD834\uDD1E". Ideally, JWS implementations SHOULD ensure
that characters outside the Basic Multilingual Plane are
preserved and compared correctly; alternatively, if this is
not possible due to these characters exercising limitations
present in the underlying JSON implementation, then input
containing them MUST be rejected.
</t>
</section>
</section>
<section title="Open Issues and Things To Be Done (TBD)" anchor="TBD">
<t>
The following items remain to be done in this draft (and related drafts):
</t>
<list style="symbols">
<t>
Consider whether there is a better term than "Digital
Signature" for the concept that includes both HMACs and
digital signatures using public keys.
</t>
<t>
Consider whether we really want to allow private header
parameter names that are not registered with IANA and are
not in collision-resistant namespaces. Eventually this
could result in interop nightmares where you need to have
different code to talk to different endpoints that "knows"
about each endpoints' private parameters.
</t>
<t>
Clarify the optional ability to provide type information in
the JWS header. Specifically, clarify the intended use of
the <spanx style="verb">typ</spanx> Header Parameter, whether it conveys syntax or
semantics, and indeed, whether this is the right approach.
Also clarify the relationship between these type values and
<xref target="RFC2045">MIME</xref> types.
</t>
<t>
Clarify the semantics of the <spanx style="verb">kid</spanx> (key ID) header
parameter. Open issues include: What happens if a kid
header is received with an unrecognized value? Is that an
error? Should it be treated as if it's empty? What happens
if the header has a recognized value but the value doesn't
match the key associated with that value, but it does match
another key that is associated with the issuer? Is that an
error?
</t>
<t>
The <spanx style="verb">x5t</spanx> parameter is currently specified as "a base64url
encoded SHA-256 thumbprint of the DER encoding of an X.509
certificate". SHA-1 was traditionally used for certificate
digests but collisions are possible to create and can be
used for denial of service attacks within multi-tenant
services. We need to understand the compatibility issues of
using SHA-256 thumbprints instead. We also likely want to
specify the digest algorithm explicitly.
</t>
<t>
Several people have objected to the requirement for
implementing RSA SHA-256, some because they will only be
using HMACs and symmetric keys, and others because they only
want to use ECDSA when using asymmetric keys, either for
security or key length reasons, or both. I believe
therefore, that we should consider changing the MUST for RSA
SHA-256 to RECOMMENDED.
</t>
<t>
Since RFC 3447 Section 8 explicitly calls for people NOT to
adopt RSASSA-PKCS1 for new applications and instead requests
that people transition to RSASSA-PSS, we probably need some
Security Considerations text explaining why RSASSA-PKCS1 is
being used (it's what's commonly implemented) and what the
potential consequences are.
</t>
<t>
Generalize the normative text on signing algorithms so that
the descriptions apply equally to the use of various key
lengths - not just HMAC SHA-256, RSA SHA-256, and ECDSA
P-256 SHA-256.
</t>
<t>
Add a table cross-referencing the algorithm name strings
used in standard software packages and specifications.
</t>
<t>
Add Security Considerations text on timing attacks.
</t>
<t>
Finish the Security Considerations section.
</t>
<t>
Sort out what to do with the IANA registries if this is
first standardized as an OpenID specification.
</t>
<t>
Write the related specification for encoding public keys
using JSON, as per the agreement documented at
http://self-issued.info/?p=390. This will be used by the
<spanx style="verb">jku</spanx> (JSON Key URL) header parameter.
</t>
<t>
Write the companion encryption specification, per the
agreements documented at http://self-issued.info/?p=378.
</t>
</list>
</section>
</middle>
<back>
<references title="Normative References">
&RFC1738;
&RFC2045;
&RFC2104;
&rfc2119;
&RFC3339;
&RFC3447;
&RFC3629;
&RFC3986;
&RFC4627;
&RFC4648;
&RFC5226;
&RFC5280;
<reference anchor="FIPS.180-3">
<front>
<title>Secure Hash Standard (SHS)</title>
<author>
<organization>National Institute of Standards and
Technology</organization>
</author>
<date month="October" year="2008" />
</front>
<format target="http://csrc.nist.gov/publications/fips/fips180-3/fips180-3_final.pdf" type="PDF" />
<seriesInfo name="FIPS" value="PUB 180-3" />
</reference>
<reference anchor="FIPS.186-3">
<front>
<title>Digital Signature Standard (DSS)</title>
<author>
<organization>National Institute of Standards and
Technology</organization>
</author>
<date month="June" year="2009" />
</front>
<format target="http://csrc.nist.gov/publications/fips/fips186-3/fips_186-3.pdf" type="PDF" />
<seriesInfo name="FIPS" value="PUB 186-3" />
</reference>
<reference anchor="USA15">
<front>
<title>Unicode Normalization Forms</title>
<author fullname="Mark Davis" initials="M." surname="Davis">
<address>
<email>markdavis@google.com</email>
</address>
</author>
<author fullname="Ken Whistler" initials="K." surname="Whistler">
<address>
<email>ken@unicode.org</email>
</address>
</author>
<author fullname="Martin Dürst" initials="M."
surname="Dürst"></author>
<date day="03" month="09" year="2009" />
</front>
<seriesInfo name="Unicode Standard Annex" value="15" />
</reference>
<reference anchor="JWT">
<front>
<title>JSON Web Token (JWT)</title>
<author fullname="Michael B. Jones" initials="M.B." surname="Jones">
<organization>Microsoft</organization>
<address>
<email>mbj@microsoft.com</email>
<uri>http://self-issued.info/</uri>
</address>
</author>
<author fullname="Dirk Balfanz" initials="D." surname="Balfanz">
<organization>Google</organization>
<address>
<email>balfanz@google.com</email>
</address>
</author>
<author fullname="John Bradley" initials="J." surname="Bradley">
<organization>independent</organization>
<address>
<email>ve7jtb@ve7jtb.com</email>
</address>
</author>
<author fullname="Yaron Y. Goland" initials="Y.Y." surname="Goland">
<organization>Microsoft</organization>
<address>
<email>yarong@microsoft.com</email>
</address>
</author>
<author fullname="John Panzer" initials="J." surname="Panzer">
<organization>Google</organization>
<address>
<email>jpanzer@google.com</email>
</address>
</author>
<author fullname="Nat Sakimura" initials="N." surname="Sakimura">
<organization>Nomura Research Institute</organization>
<address>
<email>n-sakimura@nri.co.jp</email>
</address>
</author>
<author fullname="Paul Tarjan" initials="P." surname="Tarjan">
<organization>Facebook</organization>
<address>
<email>pt@fb.com</email>
</address>
</author>
<date day="28" month="March" year="2011" />
</front>
<format target="http://self-issued.info/docs/draft-jones-json-web-token.html" type="HTML" />
</reference>
</references>
<references title="Informative References">
&RFC3275;
<reference anchor="MagicSignatures">
<front>
<title>Magic Signatures</title>
<author fullname="John Panzer (editor)" initials="J." surname="Panzer (editor)"></author>
<author fullname="Ben Laurie" initials="B." surname="Laurie"></author>
<author fullname="Dirk Balfanz" initials="D." surname="Balfanz"></author>
<date month="August" year="2010" />
</front>
<format target="http://salmon-protocol.googlecode.com/svn/trunk/draft-panzer-magicsig-experimental-00.html" type="HTML" />
</reference>
<reference anchor="JSS">
<front>
<title>JSON Simple Sign</title>
<author fullname="John Bradley" initials="J." surname="Bradley">
<organization>independent</organization>
</author>
<author fullname="Nat Sakimura (editor)" initials="N. " surname="Sakimura (editor)">
<organization>Nomura Research Institute</organization>
</author>
<date month="September" year="2010" />
</front>
<format target="http://jsonenc.info/jss/1.0/" type="HTML" />
</reference>
<reference anchor="CanvasApp">
<front>
<title>Canvas Applications</title>
<author fullname="Facebook" surname="Facebook"></author>
<date year="2010" />
</front>
<format target="http://developers.facebook.com/docs/authentication/canvas" type="HTML" />
</reference>
<reference anchor="JWE">
<front>
<title>JSON Web Encryption (JWE)</title>
<author fullname="Michael B. Jones" initials="M.B." surname="Jones">
<organization>Microsoft</organization>
<address>
<email>mbj@microsoft.com</email>
<uri>http://self-issued.info/</uri>
</address>
</author>
<author fullname="John Bradley" initials="J." surname="Bradley">
<organization>independent</organization>
<address>
<email>ve7jtb@ve7jtb.com</email>
</address>
</author>
<author fullname="Nat Sakimura" initials="N." surname="Sakimura">
<organization>Nomura Research Institute</organization>
<address>
<email>n-sakimura@nri.co.jp</email>
</address>
</author>
<date day="28" month="March" year="2011" />
</front>
<format target="http://self-issued.info/docs/draft-jones-json-web-encryption.html" type="HTML" />
</reference>
</references>
<section title="JWS Examples" anchor="JWSExamples">
<t>
This section provides several examples of JWSs. While these
examples all represent JSON Web Tokens (JWTs) <xref
target="JWT" />, note that the payload can be any base64url
encoded content.
</t>
<section title="JWS using HMAC SHA-256" anchor="HMACSHA256Example">
<section title="Encoding">
<t>
The following example JSON header object declares that the
data structure is a JSON Web Token (JWT) <xref target="JWT" />
and the JWS Signing Input is signed using
the HMAC SHA-256 algorithm. Note that white space is
explicitly allowed in Decoded JWS Header Input strings and
no canonicalization is performed before encoding.
</t>
<artwork><![CDATA[{"typ":"JWT",
"alg":"HS256"}]]></artwork>
<t>
The following byte array contains the UTF-8 characters for
the Decoded JWS Header Input:
</t>
<t>
[123, 34, 116, 121, 112, 34, 58, 34, 74, 87, 84, 34, 44, 13, 10, 32, 34, 97, 108, 103, 34, 58, 34, 72, 83, 50, 53, 54, 34, 125]
</t>
<t>
Base64url encoding this UTF-8 representation yields this
JWS Header Input value:
</t>
<artwork><![CDATA[eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9]]></artwork>
<t>
The Decoded JWS Payload Input used in this example
follows. (Note that the payload can be any base64url
encoded content, and need not be a base64url encoded JSON
object.)
</t>
<artwork><![CDATA[{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}]]></artwork>
<t>
The following byte array contains the
UTF-8 characters for the Decoded JWS Payload Input:
</t>
<t>
[123, 34, 105, 115, 115, 34, 58, 34, 106, 111, 101, 34, 44, 13, 10, 32, 34, 101, 120, 112, 34, 58, 49, 51, 48, 48, 56, 49, 57, 51, 56, 48, 44, 13, 10, 32, 34, 104, 116, 116, 112, 58, 47, 47, 101, 120, 97, 109, 112, 108, 101, 46, 99, 111, 109, 47, 105, 115, 95, 114, 111, 111, 116, 34, 58, 116, 114, 117, 101, 125]
</t>
<t>
Base64url encoding the above yields the JWS Payload Input value:
</t>
<artwork><![CDATA[eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ]]></artwork>
<t>
Concatenating the JWS Header Input, a period character,
and the JWS Payload Input yields this JWS Signing Input
value (with line breaks for display purposes only):
</t>
<artwork><![CDATA[eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ]]></artwork>
<t>
The UTF-8 representation of the JWS Signing Input is the
following byte array:
</t>
<t>
[101, 121, 74, 48, 101, 88, 65, 105, 79, 105, 74, 75, 86, 49, 81, 105, 76, 65, 48, 75, 73, 67, 74, 104, 98, 71, 99, 105, 79, 105, 74, 73, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]
</t>
<t>
HMACs are generated using keys. This example uses the key
represented by the following byte array:
</t>
<t>
[3, 35, 53, 75, 43, 15, 165, 188, 131, 126, 6, 101, 119, 123, 166, 143, 90, 179, 40, 230, 240, 84, 201, 40, 169, 15, 132, 178, 210, 80, 46, 191, 211, 251, 90, 146, 210, 6, 71, 239, 150, 138, 180, 195, 119, 98, 61, 34, 61, 46, 33, 114, 5, 46, 79, 8, 192, 205, 154, 245, 103, 208, 128, 163]
</t>
<t>
Running the HMAC SHA-256 algorithm on the UTF-8
representation of the JWS Signing Input with this key
yields the following byte array:
</t>
<t>
[116, 24, 223, 180, 151, 153, 224, 37, 79, 250, 96, 125, 216, 173, 187, 186, 22, 212, 37, 77, 105, 214, 191, 240, 91, 88, 5, 88, 83, 132, 141, 121]
</t>
<t>
Base64url encoding the above HMAC output yields the JWS Crypto
Output value:
</t>
<artwork><![CDATA[dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk]]></artwork>
</section>
<section title="Decoding">
<t>
Decoding the JWS first requires removing the base64url
encoding from the JWS Header Input, the JWS Payload
Input, and the JWS Crypto Output. We base64url decode
the inputs per <xref target="base64urllogic"></xref> and
turn them into the corresponding byte arrays. We
translate the header input byte array containing UTF-8
encoded characters into the Decoded JWS Header Input
string.
</t>
</section>
<section title="Validating">
<t>
Next we validate the decoded results. Since the "alg"
parameter in the header is "HS256", we validate the HMAC
SHA-256 signature contained in the JWS Crypto Output. If
any of the validation steps fail, the signed content MUST be
rejected.
</t>
<t>
First, we validate that the decoded JWS Header Input
string is legal JSON.
</t>
<t>
To validate the signature, we repeat the previous process
of using the correct key and the UTF-8 representation of
the JWS Signing Input as input to a SHA-256 HMAC function
and then taking the output and determining if it matches
the Decoded JWS Crypto Output. If it matches exactly,
the signature has been validated.
</t>
</section>
</section>
<section title="JWS using RSA SHA-256" anchor="RSASHA256Example">
<section title="Encoding">
<t>
The Decoded JWS Header Input in this example is different
from the previous example in two ways: First, because a
different algorithm is being used, the "alg" value is
different. Second, for illustration purposes only, the
optional "typ" parameter is not used. (This difference is
not related to the signature algorithm employed.) The
Decoded JWS Header Input used is:
</t>
<artwork><![CDATA[{"alg":"RS256"}]]></artwork>
<t>
The following byte array contains the UTF-8 characters for
the Decoded JWS Header Input:
</t>
<t>
[123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]
</t>
<t>
Base64url encoding this UTF-8 representation yields this
JWS Header Input value:
</t>
<artwork><![CDATA[eyJhbGciOiJSUzI1NiJ9]]></artwork>
<t>
The Decoded JWS Payload Input used in this example, which
follows, is the same as in the previous example. Since
the JWS Payload Input will therefore be the same, its
computation is not repeated here.
</t>
<artwork><![CDATA[{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}]]></artwork>
<t>
Concatenating the JWS Header Input, a period character,
and the JWS Payload Input yields this JWS Signing Input
value (with line breaks for display purposes only):
</t>
<artwork><![CDATA[eyJhbGciOiJSUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ]]></artwork>
<t>
The UTF-8 representation of the JWS Signing Input is the
following byte array:
</t>
<t>
[101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 83, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]
</t>
<t>
The RSA key consists of a public part (n, e), and a
private exponent d. The values of the RSA key used in
this example, presented as the byte arrays representing
big endian integers are:
</t>
<texttable>
<ttcol align="left">Parameter Name</ttcol>
<ttcol align="left">Value</ttcol>
<c>n</c>
<c>
[161, 248, 22, 10, 226, 227, 201, 180, 101, 206, 141, 45, 101, 98, 99, 54, 43, 146, 125, 190, 41, 225, 240, 36, 119, 252, 22, 37, 204, 144, 161, 54, 227, 139, 217, 52, 151, 197, 182, 234, 99, 221, 119, 17, 230, 124, 116, 41, 249, 86, 176, 251, 138, 143, 8, 154, 220, 75, 105, 137, 60, 193, 51, 63, 83, 237, 208, 25, 184, 119, 132, 37, 47, 236, 145, 79, 228, 133, 119, 105, 89, 75, 234, 66, 128, 211, 44, 15, 85, 191, 98, 148, 79, 19, 3, 150, 188, 110, 155, 223, 110, 189, 210, 189, 163, 103, 142, 236, 160, 198, 104, 247, 1, 179, 141, 191, 251, 56, 200, 52, 44, 226, 254, 109, 39, 250, 222, 74, 90, 72, 116, 151, 157, 212, 185, 207, 154, 222, 196, 199, 91, 5, 133, 44, 44, 15, 94, 248, 165, 193, 117, 3, 146, 249, 68, 232, 237, 100, 193, 16, 198, 182, 71, 96, 154, 164, 120, 58, 235, 156, 108, 154, 215, 85, 49, 48, 80, 99, 139, 131, 102, 92, 111, 111, 122, 130, 163, 150, 112, 42, 31, 100, 27, 130, 211, 235, 242, 57, 34, 25, 73, 31, 182, 134, 135, 44, 87, 22, 245, 10, 248, 53, 141, 154, 139, 157, 23, 195, 64, 114, 143, 127, 135, 216, 154, 24, 216, 252, 171, 103, 173, 132, 89, 12, 46, 207, 117, 147, 57, 54, 60, 7, 3, 77, 111, 96, 111, 158, 33, 224, 84, 86, 202, 229, 233, 161]
</c>
<c>e</c>
<c>
[1, 0, 1]
</c>
<c>d</c>
<c>
[18, 174, 113, 164, 105, 205, 10, 43, 195, 126, 82, 108, 69, 0, 87, 31, 29, 97, 117, 29, 100, 233, 73, 112, 123, 98, 89, 15, 157, 11, 165, 124, 150, 60, 64, 30, 63, 207, 47, 44, 211, 189, 236, 136, 229, 3, 191, 198, 67, 155, 11, 40, 200, 47, 125, 55, 151, 103, 31, 82, 19, 238, 216, 193, 90, 37, 216, 213, 206, 160, 2, 94, 227, 171, 46, 139, 127, 121, 33, 111, 198, 59, 234, 86, 39, 83, 180, 6, 68, 198, 161, 81, 39, 217, 178, 149, 69, 64, 160, 187, 225, 163, 5, 86, 152, 45, 78, 159, 222, 95, 100, 37, 241, 77, 75, 113, 52, 65, 181, 93, 199, 59, 155, 74, 237, 204, 146, 172, 227, 146, 126, 55, 245, 125, 12, 253, 94, 117, 129, 250, 81, 44, 143, 73, 97, 169, 235, 11, 128, 248, 168, 7, 70, 114, 138, 85, 255, 70, 71, 31, 52, 37, 6, 59, 157, 83, 100, 47, 94, 222, 30, 132, 214, 19, 8, 26, 250, 92, 34, 208, 81, 40, 91, 214, 59, 148, 59, 86, 93, 137, 138, 5, 104, 84, 19, 229, 60, 60, 108, 101, 37, 255, 31, 227, 78, 61, 220, 112, 240, 213, 100, 80, 253, 164, 139, 161, 46, 16, 78, 157, 235, 159, 184, 24, 129, 225, 196, 189, 242, 93, 146, 71, 244, 80, 200, 101, 146, 121, 104, 231, 115, 52, 244, 65, 79, 117, 167, 80, 225, 57, 84, 110, 58, 138, 115, 157]
</c>
</texttable>
<t>
The RSA private key (n, d) is then passed to the RSA
signing function, which also takes the hash type, SHA-256,
and the UTF-8 representation of the JWS Signing Input as
inputs. The result of the signature is a byte array S,
which represents a big endian integer. In this example, S
is:
</t>
<texttable>
<ttcol align="left">Result Name</ttcol>
<ttcol align="left">Value</ttcol>
<c>S</c>
<c>
[112, 46, 33, 137, 67, 232, 143, 209, 30, 181, 216, 45, 191, 120, 69, 243, 65, 6, 174, 27, 129, 255, 247, 115, 17, 22, 173, 209, 113, 125, 131, 101, 109, 66, 10, 253, 60, 150, 238, 221, 115, 162, 102, 62, 81, 102, 104, 123, 0, 11, 135, 34, 110, 1, 135, 237, 16, 115, 249, 69, 229, 130, 173, 252, 239, 22, 216, 90, 121, 142, 232, 198, 109, 219, 61, 184, 151, 91, 23, 208, 148, 2, 190, 237, 213, 217, 217, 112, 7, 16, 141, 178, 129, 96, 213, 248, 4, 12, 167, 68, 87, 98, 184, 31, 190, 127, 249, 217, 46, 10, 231, 111, 36, 242, 91, 51, 187, 230, 244, 74, 230, 30, 177, 4, 10, 203, 32, 4, 77, 62, 249, 18, 142, 212, 1, 48, 121, 91, 212, 189, 59, 65, 238, 202, 208, 102, 171, 101, 25, 129, 253, 228, 141, 247, 127, 55, 45, 195, 139, 159, 175, 221, 59, 239, 177, 139, 93, 163, 204, 60, 46, 176, 47, 158, 58, 65, 214, 18, 202, 173, 21, 145, 18, 115, 160, 95, 35, 185, 232, 56, 250, 175, 132, 157, 105, 132, 41, 239, 90, 30, 136, 121, 130, 54, 195, 212, 14, 96, 69, 34, 165, 68, 200, 242, 122, 122, 45, 184, 6, 99, 209, 108, 247, 202, 234, 86, 222, 64, 92, 178, 33, 90, 69, 178, 194, 85, 102, 181, 90, 193, 167, 72, 160, 112, 223, 200, 163, 42, 70, 149, 67, 208, 25, 238, 251, 71]
</c>
</texttable>
<t>
Base64url encoding the signature produces this value for
the JWS Crypto Output:
</t>
<artwork><![CDATA[cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqvhJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrBp0igcN_IoypGlUPQGe77Rw]]></artwork>
</section>
<section title="Decoding">
<t>
Decoding the JWS from this example requires processing the
JWS Header Input and JWS Payload Input exactly as
done in the first example.
</t>
</section>
<section title="Validating">
<t>
Since the "alg" parameter in the header is "RS256", we
validate the RSA SHA-256 signature contained in the JWS
Crypto Output. If any of the validation steps fail, the
signed content MUST be rejected.
</t>
<t>
First, we validate that the decoded JWS Header Input
string is legal JSON.
</t>
<t>
Validating the JWS Crypto Output is a little different
from the previous example. First, we base64url decode the
JWS Crypto Output to produce a signature S to check. We
then pass (n, e), S and the UTF-8 representation of the
JWS Signing Input to an RSA signature verifier that has
been configured to use the SHA-256 hash function.
</t>
</section>
</section>
<section title="JWS using ECDSA P-256 SHA-256" anchor="ECDSASHA256Example">
<section title="Encoding">
<t>
The Decoded JWS Header Input for this example differs from
the previous example because a different algorithm is
being used. The Decoded JWS Header Input used is:
</t>
<artwork><![CDATA[{"alg":"ES256"}]]></artwork>
<t>
The following byte array contains the UTF-8 characters for
the Decoded JWS Header Input:
</t>
<t>
[123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]
</t>
<t>
Base64url encoding this UTF-8 representation yields this
JWS Header Input value:
</t>
<artwork><![CDATA[eyJhbGciOiJFUzI1NiJ9]]></artwork>
<t>
The Decoded JWS Payload Input used in this example, which
follows, is the same as in the previous examples. Since
the JWS Payload Input will therefore be the same, its
computation is not repeated here.
</t>
<artwork><![CDATA[{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}]]></artwork>
<t>
Concatenating the JWS Header Input, a period character,
and the JWS Payload Input yields this JWS Signing Input
value (with line breaks for display purposes only):
</t>
<artwork><![CDATA[eyJhbGciOiJFUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFtcGxlLmNvbS9pc19yb290Ijp0cnVlfQ]]></artwork>
<t>
The UTF-8 representation of the JWS Signing Input is the
following byte array:
</t>
<t>
[101, 121, 74, 104, 98, 71, 99, 105, 79, 105, 74, 70, 85, 122, 73, 49, 78, 105, 74, 57, 46, 101, 121, 74, 112, 99, 51, 77, 105, 79, 105, 74, 113, 98, 50, 85, 105, 76, 65, 48, 75, 73, 67, 74, 108, 101, 72, 65, 105, 79, 106, 69, 122, 77, 68, 65, 52, 77, 84, 107, 122, 79, 68, 65, 115, 68, 81, 111, 103, 73, 109, 104, 48, 100, 72, 65, 54, 76, 121, 57, 108, 101, 71, 70, 116, 99, 71, 120, 108, 76, 109, 78, 118, 98, 83, 57, 112, 99, 49, 57, 121, 98, 50, 57, 48, 73, 106, 112, 48, 99, 110, 86, 108, 102, 81]
</t>
<t>
The ECDSA key consists of a public part, the EC point (x,
y), and a private part d. The values of the ECDSA key
used in this example, presented as the byte arrays
representing big endian integers are:
</t>
<texttable>
<ttcol align="left">Parameter Name</ttcol>
<ttcol align="left">Value</ttcol>
<c>x</c>
<c>
[127, 205, 206, 39, 112, 246, 196, 93, 65, 131, 203, 238, 111, 219, 75, 123, 88, 7, 51, 53, 123, 233, 239, 19, 186, 207, 110, 60, 123, 209, 84, 69]
</c>
<c>y</c>
<c>
[199, 241, 68, 205, 27, 189, 155, 126, 135, 44, 223, 237, 185, 238, 185, 244, 179, 105, 93, 110, 169, 11, 36, 173, 138, 70, 35, 40, 133, 136, 229, 173]
</c>
<c>d</c>
<c>
[142, 155, 16, 158, 113, 144, 152, 191, 152, 4, 135, 223, 31, 93, 119, 233, 203, 41, 96, 110, 190, 210, 38, 59, 95, 87, 194, 19, 223, 132, 244, 178]
</c>
</texttable>
<t>
The ECDSA private part d is then passed to an ECDSA
signing function, which also takes the curve type, P-256,
the hash type, SHA-256, and the UTF-8 representation of
the JWS Signing Input as inputs. The result of the
signature is the EC point (R, S), where R and S are
unsigned integers. In this example, the R and S values,
given as byte arrays representing big endian integers are:
</t>
<texttable>
<ttcol align="left">Result Name</ttcol>
<ttcol align="left">Value</ttcol>
<c>R</c>
<c>
[14, 209, 33, 83, 121, 99, 108, 72, 60, 47, 127, 21, 88, 7, 212, 2, 163, 178, 40, 3, 58, 249, 124, 126, 23, 129, 154, 195, 22, 158, 166, 101]
</c>
<c>S</c>
<c>
[197, 10, 7, 211, 140, 60, 112, 229, 216, 241, 45, 175, 8, 74, 84, 128, 166, 101, 144, 197, 242, 147, 80, 154, 143, 63, 127, 138, 131, 163, 84, 213]
</c>
</texttable>
<t>
Concatenating the S array to the end of the R array and
base64url encoding the result produces this value for the
JWS Crypto Output:
</t>
<artwork><![CDATA[DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSApmWQxfKTUJqPP3-Kg6NU1Q]]></artwork>
</section>
<section title="Decoding">
<t>
Decoding the JWS from this example requires processing the
JWS Header Input and JWS Payload Input exactly as
done in the first example.
</t>
</section>
<section title="Validating">
<t>
Since the "alg" parameter in the header is "ES256", we
validate the ECDSA P-256 SHA-256 signature contained in
the JWS Crypto Output. If any of the validation steps
fail, the signed content MUST be rejected.
</t>
<t>
First, we validate that the decoded JWS Header Input
string is legal JSON.
</t>
<t>
Validating the JWS Crypto Output is a little different
from the first example. First, we base64url decode the JWS
Crypto Output as in the previous examples but we then
need to split the 64 member byte array that must result
into two 32 byte arrays, the first R and the second S. We
then pass (x, y), (R, S) and the UTF-8 representation of
the JWS Signing Input to an ECDSA signature verifier that
has been configured to use the P-256 curve with the
SHA-256 hash function.
</t>
<t>
As explained in <xref target="DefiningECDSA"></xref>, the
use of the k value in ECDSA means that we cannot validate
the correctness of the signature in the same way we
validated the correctness of the HMAC. Instead,
implementations MUST use an ECDSA validator to validate
the signature.
</t>
</section>
</section>
</section>
<section title="Notes on implementing base64url encoding without padding" anchor="base64urlnotes">
<t>
This appendix describes how to implement base64url encoding
and decoding functions without padding based upon standard
base64 encoding and decoding functions that do use padding.
</t>
<t>
To be concrete, example C# code implementing these functions
is shown below. Similar code could be used in other
languages.
</t>
<artwork><![CDATA[static string base64urlencode(byte [] arg)
{
string s = Convert.ToBase64String(arg); // Standard base64 encoder
s = s.Split('=')[0]; // Remove any trailing '='s
s = s.Replace('+', '-'); // 62nd char of encoding
s = s.Replace('/', '_'); // 63rd char of encoding
return s;
}
static byte [] base64urldecode(string arg)
{
string s = arg;
s = s.Replace('-', '+'); // 62nd char of encoding
s = s.Replace('_', '/'); // 63rd char of encoding
switch (s.Length % 4) // Pad with trailing '='s
{
case 0: break; // No pad chars in this case
case 2: s += "=="; break; // Two pad chars
case 3: s += "="; break; // One pad char
default: throw new System.Exception(
"Illegal base64url string!");
}
return Convert.FromBase64String(s); // Standard base64 decoder
}]]></artwork>
<t>
As per the example code above, the number of '=' padding
characters that needs to be added to the end of a base64url
encoded string without padding to turn it into one with
padding is a deterministic function of the length of the
encoded string. Specifically,
if the length mod 4 is 0, no padding is added;
if the length mod 4 is 2, two '=' padding characters are added;
if the length mod 4 is 3, one '=' padding character is added;
if the length mod 4 is 1, the input is malformed.
</t>
<t>
An example correspondence between unencoded and encoded values
follows. The byte sequence below encodes into the string
below, which when decoded, reproduces the byte sequence.
</t>
<artwork>3 236 255 224 193</artwork>
<artwork>A-z_4ME</artwork>
</section>
<section title="Acknowledgements" anchor="Acknowledgements">
<t>
Solutions for signing JSON content were previously explored by
<xref target="MagicSignatures">Magic Signatures</xref>, <xref
target="JSS">JSON Simple Sign</xref>, and <xref
target="CanvasApp">Canvas Applications</xref>, all of which
influenced this draft.
</t>
</section>
<section title='Document History'>
<t>
-00
<list style='symbols'>
<t>
Created first signature draft using content split from
draft-jones-json-web-token-01. This split introduced no
semantic changes.
</t>
</list>
</t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 19:51:50 |