JSON Web Signature (JWS)
draft-ietf-jose-json-web-signature-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7515.
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|---|---|---|---|
| Authors | Nat Sakimura , Michael B. Jones , John Bradley | ||
| Last updated | 2012-01-16 | ||
| Replaces | draft-jones-json-web-signature | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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draft-ietf-jose-json-web-signature-00
JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track J. Bradley
Expires: July 19, 2012 independent
N. Sakimura
Nomura Research Institute
January 16, 2012
JSON Web Signature (JWS)
draft-ietf-jose-json-web-signature-00
Abstract
JSON Web Signature (JWS) is a means of representing content secured
with digital signatures or Hash-based Message Authentication Codes
(HMACs) using JSON data structures. Cryptographic algorithms and
identifiers used with this specification are enumerated in the
separate JSON Web Algorithms (JWA) specification. Related encryption
capabilities are described in the separate JSON Web Encryption (JWE)
specification.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on July 19, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
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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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. JSON Web Signature (JWS) Overview . . . . . . . . . . . . . . 5
3.1. Example JWS . . . . . . . . . . . . . . . . . . . . . . . 5
4. JWS Header . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Reserved Header Parameter Names . . . . . . . . . . . . . 6
4.2. Public Header Parameter Names . . . . . . . . . . . . . . 10
4.3. Private Header Parameter Names . . . . . . . . . . . . . . 10
5. Rules for Creating and Validating a JWS . . . . . . . . . . . 10
6. Securing JWSs with Cryptographic Algorithms . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8.1. Unicode Comparison Security Issues . . . . . . . . . . . . 13
9. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Appendix A. JWS Examples . . . . . . . . . . . . . . . . . . . . 16
A.1. JWS using HMAC SHA-256 . . . . . . . . . . . . . . . . . . 17
A.1.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 17
A.1.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 18
A.1.3. Validating . . . . . . . . . . . . . . . . . . . . . . 19
A.2. JWS using RSA SHA-256 . . . . . . . . . . . . . . . . . . 19
A.2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 19
A.2.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 22
A.2.3. Validating . . . . . . . . . . . . . . . . . . . . . . 22
A.3. JWS using ECDSA P-256 SHA-256 . . . . . . . . . . . . . . 23
A.3.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . 23
A.3.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . 25
A.3.3. Validating . . . . . . . . . . . . . . . . . . . . . . 25
Appendix B. Notes on implementing base64url encoding without
padding . . . . . . . . . . . . . . . . . . . . . . . 25
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 26
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Appendix D. Document History . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
JSON Web Signature (JWS) is a compact format for representing content
secured with digital signatures or Hash-based Message Authentication
Codes (HMACs) intended for space constrained environments such as
HTTP Authorization headers and URI query parameters. It represents
this content using JSON [RFC4627] data structures. The JWS digital
signature and HMAC mechanisms are independent of the type of content
being secured, allowing arbitrary content to be secured.
Cryptographic algorithms and identifiers used with this specification
are enumerated in the separate JSON Web Algorithms (JWA) [JWA]
specification. Related encryption capabilities are described in the
separate JSON Web Encryption (JWE) [JWE] specification.
2. Terminology
JSON Web Signature (JWS) A data structure cryptographically securing
a JWS Header and a JWS Payload with a JWS Signature value.
JWS Header A string representing a JSON object that describes the
digital signature or HMAC applied to the JWS Header and the JWS
Payload to create the JWS Signature value.
JWS Payload The bytes to be secured - a.k.a., the message.
JWS Signature A byte array containing the cryptographic material
that secures the contents of the JWS Header and the JWS Payload.
Encoded JWS Header Base64url encoding of the bytes of the UTF-8 RFC
3629 [RFC3629] representation of the JWS Header.
Encoded JWS Payload Base64url encoding of the JWS Payload.
Encoded JWS Signature Base64url encoding of the JWS Signature.
JWS Secured Input The concatenation of the Encoded JWS Header, a
period ('.') character, and the Encoded JWS Payload.
Header Parameter Names The names of the members within the JSON
object represented in a JWS Header.
Header Parameter Values The values of the members within the JSON
object represented in a JWS Header.
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Base64url Encoding For the purposes of this specification, this term
always refers to the URL- and filename-safe Base64 encoding
described in RFC 4648 [RFC4648], Section 5, with the (non URL-
safe) '=' padding characters omitted, as permitted by Section 3.2.
(See Appendix B for notes on implementing base64url encoding
without padding.)
3. JSON Web Signature (JWS) Overview
JWS represents digitally signed or HMACed content using JSON data
structures and base64url encoding. The representation consists of
three parts: the JWS Header, the JWS Payload, and the JWS Signature.
The three parts are base64url-encoded for transmission, and typically
represented as the concatenation of the encoded strings in that
order, with the three strings being separated by period ('.')
characters.
The JWS Header describes the signature or HMAC method and parameters
employed. The JWS Payload is the message content to be secured. The
JWS Signature ensures the integrity of both the JWS Header and the
JWS Payload.
3.1. Example JWS
The following example JWS Header declares that the encoded object is
a JSON Web Token (JWT) [JWT] and the JWS Header and the JWS Payload
are secured using the HMAC SHA-256 algorithm:
{"typ":"JWT",
"alg":"HS256"}
Base64url encoding the bytes of the UTF-8 representation of the JWS
Header yields this Encoded JWS Header value:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
The following is an example of a JSON object that can be used as a
JWS Payload. (Note that the payload can be any content, and need not
be a representation of a JSON object.)
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Base64url encoding the bytes of the UTF-8 representation of the JSON
object yields the following Encoded JWS Payload (with line breaks for
display purposes only):
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
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Computing the HMAC of the UTF-8 representation of the JWS Secured
Input (the concatenation of the Encoded JWS Header, a period ('.')
character, and the Encoded JWS Payload) with the HMAC SHA-256
algorithm and base64url encoding the result, as per Appendix A.1,
yields this Encoded JWS Signature value:
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
Concatenating these parts in the order Header.Payload.Signature with
period characters between the parts yields this complete JWS
representation (with line breaks for display purposes only):
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
.
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
This computation is illustrated in more detail in Appendix A.1.
4. JWS Header
The members of the JSON object represented by the JWS Header describe
the digital signature or HMAC applied to the Encoded JWS Header and
the Encoded JWS Payload and optionally additional properties of the
JWS. The Header Parameter Names within this object MUST be unique.
Implementations MUST understand the entire contents of the header;
otherwise, the JWS MUST be rejected.
The JWS Header MUST contain an "alg" (algorithm) parameter, the value
of which is a string that unambiguously identifies the algorithm used
to secure the JWS Header and the JWS Payload to produce the JWS
Signature.
There are three classes of Header Parameter Names: Reserved Header
Parameter Names, Public Header Parameter Names, and Private Header
Parameter Names.
4.1. Reserved Header Parameter Names
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.
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+-----------+--------+-------------+--------------------------------+
| Header | JSON | Header | Header Parameter Semantics |
| Parameter | Value | Parameter | |
| Name | Type | Syntax | |
+-----------+--------+-------------+--------------------------------+
| alg | string | StringOrURI | The "alg" (algorithm) header |
| | | | parameter identifies the |
| | | | cryptographic algorithm used |
| | | | to secure the JWS. A list of |
| | | | defined "alg" values is |
| | | | presented in Section 3, Table |
| | | | 1 of the JSON Web Algorithms |
| | | | (JWA) [JWA] specification. |
| | | | The processing of the "alg" |
| | | | header parameter requires that |
| | | | the value MUST be one that is |
| | | | both supported and for which |
| | | | there exists a key for use |
| | | | with that algorithm associated |
| | | | with the party that digitally |
| | | | signed or HMACed the content. |
| | | | The "alg" parameter value is |
| | | | case sensitive. This header |
| | | | parameter is REQUIRED. |
| typ | string | String | The "typ" (type) header |
| | | | parameter is used to declare |
| | | | the type of the secured |
| | | | content. The "typ" value is |
| | | | case sensitive. This header |
| | | | parameter is OPTIONAL. |
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| jku | string | URL | The "jku" (JSON Web Key URL) |
| | | | header parameter is an |
| | | | absolute URL that refers to a |
| | | | resource for a set of |
| | | | JSON-encoded public keys, one |
| | | | of which corresponds to the |
| | | | key that was used to digitally |
| | | | sign the JWS. The keys MUST |
| | | | be encoded as described in the |
| | | | JSON Web Key (JWK) [JWK] |
| | | | specification. The protocol |
| | | | used to acquire the resource |
| | | | MUST provide integrity |
| | | | protection. An HTTP GET |
| | | | request to retrieve the |
| | | | certificate MUST use TLS RFC |
| | | | 2818 [RFC2818] RFC 5246 |
| | | | [RFC5246] with server |
| | | | authentication RFC 6125 |
| | | | [RFC6125]. This header |
| | | | parameter is OPTIONAL. |
| kid | string | String | The "kid" (key ID) header |
| | | | parameter is a hint indicating |
| | | | which specific key owned by |
| | | | the signer should be used to |
| | | | validate the digital |
| | | | signature. This allows |
| | | | signers to explicitly signal a |
| | | | change of key to recipients. |
| | | | The interpretation of the |
| | | | contents of the "kid" |
| | | | parameter is unspecified. |
| | | | This header parameter is |
| | | | OPTIONAL. |
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| x5u | string | URL | The "x5u" (X.509 URL) header |
| | | | parameter is an absolute URL |
| | | | that refers to a resource for |
| | | | the X.509 public key |
| | | | certificate or certificate |
| | | | chain corresponding to the key |
| | | | used to digitally sign the |
| | | | JWS. The identified resource |
| | | | MUST provide a representation |
| | | | of the certificate or |
| | | | certificate chain that |
| | | | conforms to RFC 5280 [RFC5280] |
| | | | in PEM encoded form RFC 1421 |
| | | | [RFC1421]. The protocol used |
| | | | to acquire the resource MUST |
| | | | provide integrity protection. |
| | | | An HTTP GET request to |
| | | | retrieve the certificate MUST |
| | | | use TLS RFC 2818 [RFC2818] RFC |
| | | | 5246 [RFC5246] with server |
| | | | authentication RFC 6125 |
| | | | [RFC6125]. This header |
| | | | parameter is OPTIONAL. |
| x5t | string | String | The "x5t" (x.509 certificate |
| | | | thumbprint) header parameter |
| | | | provides a base64url encoded |
| | | | SHA-1 thumbprint (a.k.a. |
| | | | digest) of the DER encoding of |
| | | | an X.509 certificate that can |
| | | | be used to match the |
| | | | certificate. This header |
| | | | parameter is OPTIONAL. |
+-----------+--------+-------------+--------------------------------+
Table 1: Reserved Header Parameter Definitions
Additional reserved header parameter names MAY be defined via the
IANA JSON Web Signature Header Parameters registry, as per Section 7.
The syntax values used above are defined as follows:
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+-------------+-----------------------------------------------------+
| Syntax Name | Syntax Definition |
+-------------+-----------------------------------------------------+
| IntDate | The number of seconds from 1970-01-01T0:0:0Z as |
| | measured in UTC until the desired date/time. See |
| | RFC 3339 [RFC3339] for details regarding date/times |
| | in general and UTC in particular. |
| String | Any string value MAY be used. |
| StringOrURI | Any string value MAY be used but a value containing |
| | a ":" character MUST be a URI as defined in RFC |
| | 3986 [RFC3986]. |
| URL | A URL as defined in RFC 1738 [RFC1738]. |
+-------------+-----------------------------------------------------+
Table 2: Header Parameter Syntax Definitions
4.2. Public Header Parameter Names
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 needs to take reasonable precautions to make
sure they are in control of the part of the namespace they use to
define the header parameter name.
New header parameters should be introduced sparingly, as they can
result in non-interoperable JWSs.
4.3. Private Header Parameter Names
A producer and consumer of a JWS may agree to any header parameter
name that is not a Reserved Name Section 4.1 or a Public Name
Section 4.2. Unlike Public Names, these private names are subject to
collision and should be used with caution.
New header parameters should be introduced sparingly, as they can
result in non-interoperable JWSs.
5. Rules for Creating and Validating a JWS
To create a JWS, one MUST perform these steps:
1. Create the content to be used as the JWS Payload.
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2. Base64url encode the bytes of the JWS Payload. This encoding
becomes the Encoded JWS Payload.
3. Create a JWS Header containing the desired set of header
parameters. Note that white space is explicitly allowed in the
representation and no canonicalization is performed before
encoding.
4. Base64url encode the bytes of the UTF-8 representation of the JWS
Header to create the Encoded JWS Header.
5. Compute the JWS Signature in the manner defined for the
particular algorithm being used. The JWS Secured Input is always
the concatenation of the Encoded JWS Header, a period ('.')
character, and the Encoded JWS Payload. (Note that if the JWS
represents a JWT, this corresponds to the portion of the JWT
representation preceding the second period character.) The "alg"
(algorithm) header parameter MUST be present in the JSON Header,
with the algorithm value accurately representing the algorithm
used to construct the JWS Signature.
6. Base64url encode the representation of the JWS Signature to
create the Encoded JWS Signature.
When validating a JWS, the following steps MUST be taken. If any of
the listed steps fails, then the JWS MUST be rejected.
1. The Encoded JWS Header MUST be successfully base64url decoded
following the restriction given in this specification that no
padding characters have been used.
2. The JWS Header MUST be completely valid JSON syntax conforming to
RFC 4627 [RFC4627].
3. The JWS Header MUST be validated to only include parameters and
values whose syntax and semantics are both understood and
supported.
4. The Encoded JWS Payload MUST be successfully base64url decoded
following the restriction given in this specification that no
padding characters have been used.
5. The Encoded JWS Signature MUST be successfully base64url decoded
following the restriction given in this specification that no
padding characters have been used.
6. The JWS Signature MUST be successfully validated against the JWS
Header and JWS Payload in the manner defined for the algorithm
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being used, which MUST be accurately represented by the value of
the "alg" (algorithm) header parameter, which MUST be present.
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 "alg" will be checked against the
member names in the JWS Header to see if there is a matching header
parameter name. A similar process occurs when determining if the
value of the "alg" header parameter represents a supported algorithm.
Comparisons between JSON strings and other Unicode strings MUST be
performed as specified below:
1. Remove any JSON applied escaping to produce an array of Unicode
code points.
2. Unicode Normalization [USA15] MUST NOT be applied at any point to
either the JSON string or to the string it is to be compared
against.
3. Comparisons between the two strings MUST be performed as a
Unicode code point to code point equality comparison.
6. Securing JWSs with Cryptographic Algorithms
JWS uses cryptographic algorithms to digitally sign or HMAC the
contents of the JWS Header and the JWS Payload. The JSON Web
Algorithms (JWA) [JWA] specification enumerates a set of
cryptographic algorithms and identifiers to be used with this
specification. Specifically, Section 3, Table 1 enumerates a set of
"alg" (algorithm) header parameter values intended for use this
specification. It also describes the semantics and operations that
are specific to these algorithms and algorithm families.
Public keys employed for digital signing can be identified using the
Header Parameter methods described in Section 4.1 or can be
distributed using methods that are outside the scope of this
specification.
7. IANA Considerations
This specification calls for:
o A new IANA registry entitled "JSON Web Signature Header
Parameters" for reserved header parameter names is defined in
Section 4.1. Inclusion in the registry is RFC Required in the RFC
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5226 [RFC5226] 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 Table 1.
8. Security Considerations
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.
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. One example
of malformed JSON that MUST be rejected is an object in which the
same member name occurs multiple times.
TBD: Write security considerations about the implications of using a
SHA-1 hash (for compatibility reasons) for the "x5t" (x.509
certificate thumbprint).
When utilizing TLS to retrieve information, the authority providing
the resource MUST be authenticated and the information retrieved MUST
be free from modification.
8.1. Unicode Comparison Security Issues
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 RFC 4627 [RFC4627],
Section 2.5).
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").
JSON strings MAY contain characters outside the Unicode Basic
Multilingual Plane. For instance, the G clef character (U+1D11E) may
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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.
9. Open Issues and Things To Be Done (TBD)
The following items remain to be done in this draft:
o Clarify the optional ability to provide type information in the
JWS header. Specifically, clarify the intended use of the "typ"
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 MIME [RFC2045] types.
o Clarify the semantics of the "kid" (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?
o Consider whether a key type parameter should also be introduced.
o Add Security Considerations text on timing attacks.
o It would be good to have a confirmation method element so it could
be used with holder-of-key.
o Consider whether to add parameters for directly including keys in
the header, either as JWK Key Objects, or X.509 cert values, or
both.
o Consider whether to add version numbers.
o Think about how to best describe the concept currently described
as "the bytes of the UTF-8 representation of". Possible terms to
use instead of "bytes of" include "byte sequence", "octet series",
and "octet sequence". Also consider whether we want to add an
overall clarifying statement somewhere in each spec something like
"every place we say 'the UTF-8 representation of X', we mean 'the
bytes of the UTF-8 representation of X'". That would potentially
allow us to omit the "the bytes of" part everywhere else.
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o Finish the Security Considerations section.
o Add an example in which the payload is not a base64url encoded
JSON object.
10. References
10.1. Normative References
[JWA] Jones, M., "JSON Web Algorithms (JWA)", January 2012.
[JWK] Jones, M., "JSON Web Key (JWK)", January 2012.
[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication
Procedures", RFC 1421, February 1993.
[RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the
Internet: Timestamps", RFC 3339, July 2002.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
Jones, et al. Expires July 19, 2012 [Page 15]
Internet-Draft JSON Web Signature (JWS) January 2012
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[USA15] Davis, M., Whistler, K., and M. Duerst, "Unicode
Normalization Forms", Unicode Standard Annex 15, 09 2009.
10.2. Informative References
[CanvasApp]
Facebook, "Canvas Applications", 2010.
[JSS] Bradley, J. and N. Sakimura (editor), "JSON Simple Sign",
September 2010.
[JWE] Jones, M., Rescorla, E., and J. Hildebrand, "JSON Web
Encryption (JWE)", January 2012.
[JWT] Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer,
J., Sakimura, N., and P. Tarjan, "JSON Web Token (JWT)",
December 2011.
[MagicSignatures]
Panzer (editor), J., Laurie, B., and D. Balfanz, "Magic
Signatures", August 2010.
Appendix A. JWS Examples
This section provides several examples of JWSs. While these examples
all represent JSON Web Tokens (JWTs) [JWT], the payload can be any
base64url encoded content.
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A.1. JWS using HMAC SHA-256
A.1.1. Encoding
The following example JWS Header declares that the data structure is
a JSON Web Token (JWT) [JWT] and the JWS Secured Input is secured
using the HMAC SHA-256 algorithm. Note that white space is
explicitly allowed in JWS Header strings and no canonicalization is
performed before encoding.
{"typ":"JWT",
"alg":"HS256"}
The following byte array contains the UTF-8 characters for the JWS
Header:
[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]
Base64url encoding this UTF-8 representation yields this Encoded JWS
Header value:
eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
The JWS Payload used in this example follows. (Note that the payload
can be any base64url encoded content, and need not be a base64url
encoded JSON object.)
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
The following byte array contains the UTF-8 characters for the JWS
Payload:
[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]
Base64url encoding the above yields the Encoded JWS Payload value
(with line breaks for display purposes only):
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
Concatenating the Encoded JWS Header, a period character, and the
Encoded JWS Payload yields this JWS Secured Input value (with line
breaks for display purposes only):
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eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The UTF-8 representation of the JWS Secured Input is the following
byte array:
[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]
HMACs are generated using keys. This example uses the key
represented by the following byte array:
[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]
Running the HMAC SHA-256 algorithm on the UTF-8 representation of the
JWS Secured Input with this key yields the following byte array:
[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]
Base64url encoding the above HMAC output yields the Encoded JWS
Signature value:
dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk
A.1.2. Decoding
Decoding the JWS first requires removing the base64url encoding from
the Encoded JWS Header, the Encoded JWS Payload, and the Encoded JWS
Signature. We base64url decode the inputs and turn them into the
corresponding byte arrays. We translate the header input byte array
containing UTF-8 encoded characters into the JWS Header string.
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A.1.3. Validating
Next we validate the decoded results. Since the "alg" parameter in
the header is "HS256", we validate the HMAC SHA-256 value contained
in the JWS Signature. If any of the validation steps fail, the JWS
MUST be rejected.
First, we validate that the JWS Header string is legal JSON.
To validate the HMAC value, we repeat the previous process of using
the correct key and the UTF-8 representation of the JWS Secured Input
as input to a SHA-256 HMAC function and then taking the output and
determining if it matches the JWS Signature. If it matches exactly,
the HMAC has been validated.
A.2. JWS using RSA SHA-256
A.2.1. Encoding
The JWS Header 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 algorithm employed.) The JWS Header used is:
{"alg":"RS256"}
The following byte array contains the UTF-8 characters for the JWS
Header:
[123, 34, 97, 108, 103, 34, 58, 34, 82, 83, 50, 53, 54, 34, 125]
Base64url encoding this UTF-8 representation yields this Encoded JWS
Header value:
eyJhbGciOiJSUzI1NiJ9
The JWS Payload used in this example, which follows, is the same as
in the previous example. Since the Encoded JWS Payload will
therefore be the same, its computation is not repeated here.
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Concatenating the Encoded JWS Header, a period character, and the
Encoded JWS Payload yields this JWS Secured Input value (with line
breaks for display purposes only):
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eyJhbGciOiJSUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The UTF-8 representation of the JWS Secured Input is the following
byte array:
[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]
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:
+-----------+-------------------------------------------------------+
| Parameter | Value |
| Name | |
+-----------+-------------------------------------------------------+
| n | [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] |
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| e | [1, 0, 1] |
| d | [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] |
+-----------+-------------------------------------------------------+
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 Secured Input as inputs. The result of the
digital signature is a byte array S, which represents a big endian
integer. In this example, S is:
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+--------+----------------------------------------------------------+
| Result | Value |
| Name | |
+--------+----------------------------------------------------------+
| S | [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] |
+--------+----------------------------------------------------------+
Base64url encoding the digital signature produces this value for the
Encoded JWS Signature (with line breaks for display purposes only):
cC4hiUPoj9Eetdgtv3hF80EGrhuB__dzERat0XF9g2VtQgr9PJbu3XOiZj5RZmh7
AAuHIm4Bh-0Qc_lF5YKt_O8W2Fp5jujGbds9uJdbF9CUAr7t1dnZcAcQjbKBYNX4
BAynRFdiuB--f_nZLgrnbyTyWzO75vRK5h6xBArLIARNPvkSjtQBMHlb1L07Qe7K
0GarZRmB_eSN9383LcOLn6_dO--xi12jzDwusC-eOkHWEsqtFZESc6BfI7noOPqv
hJ1phCnvWh6IeYI2w9QOYEUipUTI8np6LbgGY9Fs98rqVt5AXLIhWkWywlVmtVrB
p0igcN_IoypGlUPQGe77Rw
A.2.2. Decoding
Decoding the JWS from this example requires processing the Encoded
JWS Header and Encoded JWS Payload exactly as done in the first
example.
A.2.3. Validating
Since the "alg" parameter in the header is "RS256", we validate the
RSA SHA-256 digital signature contained in the JWS Signature. If any
of the validation steps fail, the JWS MUST be rejected.
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First, we validate that the JWS Header string is legal JSON.
Validating the JWS Signature is a little different from the previous
example. First, we base64url decode the Encoded JWS Signature to
produce a digital signature S to check. We then pass (n, e), S and
the UTF-8 representation of the JWS Secured Input to an RSA signature
verifier that has been configured to use the SHA-256 hash function.
A.3. JWS using ECDSA P-256 SHA-256
A.3.1. Encoding
The JWS Header for this example differs from the previous example
because a different algorithm is being used. The JWS Header used is:
{"alg":"ES256"}
The following byte array contains the UTF-8 characters for the JWS
Header:
[123, 34, 97, 108, 103, 34, 58, 34, 69, 83, 50, 53, 54, 34, 125]
Base64url encoding this UTF-8 representation yields this Encoded JWS
Header value:
eyJhbGciOiJFUzI1NiJ9
The JWS Payload used in this example, which follows, is the same as
in the previous examples. Since the Encoded JWS Payload will
therefore be the same, its computation is not repeated here.
{"iss":"joe",
"exp":1300819380,
"http://example.com/is_root":true}
Concatenating the Encoded JWS Header, a period character, and the
Encoded JWS Payload yields this JWS Secured Input value (with line
breaks for display purposes only):
eyJhbGciOiJFUzI1NiJ9
.
eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt
cGxlLmNvbS9pc19yb290Ijp0cnVlfQ
The UTF-8 representation of the JWS Secured Input is the following
byte array:
[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,
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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]
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:
+-----------+-------------------------------------------------------+
| Parameter | Value |
| Name | |
+-----------+-------------------------------------------------------+
| x | [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] |
| y | [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] |
| d | [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] |
+-----------+-------------------------------------------------------+
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 Secured Input as inputs. The
result of the digital 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:
+--------+----------------------------------------------------------+
| Result | Value |
| Name | |
+--------+----------------------------------------------------------+
| R | [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] |
| S | [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] |
+--------+----------------------------------------------------------+
Concatenating the S array to the end of the R array and base64url
encoding the result produces this value for the Encoded JWS Signature
(with line breaks for display purposes only):
DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA
pmWQxfKTUJqPP3-Kg6NU1Q
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A.3.2. Decoding
Decoding the JWS from this example requires processing the Encoded
JWS Header and Encoded JWS Payload exactly as done in the first
example.
A.3.3. Validating
Since the "alg" parameter in the header is "ES256", we validate the
ECDSA P-256 SHA-256 digital signature contained in the JWS Signature.
If any of the validation steps fail, the JWS MUST be rejected.
First, we validate that the JWS Header string is legal JSON.
Validating the JWS Signature is a little different from the first
example. First, we base64url decode the Encoded JWS Signature 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 Secured Input to an ECDSA signature verifier that has been
configured to use the P-256 curve with the SHA-256 hash function.
As explained in Section 3.3 of the JSON Web Algorithms (JWA) [JWA]
specification, the use of the k value in ECDSA means that we cannot
validate the correctness of the digital signature in the same way we
validated the correctness of the HMAC. Instead, implementations MUST
use an ECDSA validator to validate the digital signature.
Appendix B. Notes on implementing base64url encoding without padding
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.
To be concrete, example C# code implementing these functions is shown
below. Similar code could be used in other languages.
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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
}
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.
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.
3 236 255 224 193
A-z_4ME
Appendix C. Acknowledgements
Solutions for signing JSON content were previously explored by Magic
Signatures [MagicSignatures], JSON Simple Sign [JSS], and Canvas
Applications [CanvasApp], all of which influenced this draft. Dirk
Balfanz, Yaron Y. Goland, John Panzer, and Paul Tarjan all made
significant contributions to the design of this specification.
Jones, et al. Expires July 19, 2012 [Page 26]
Internet-Draft JSON Web Signature (JWS) January 2012
Appendix D. Document History
-00
o Created the initial IETF draft based upon
draft-jones-json-web-signature-04 with no normative changes.
o Changed terminology to no longer call both digital signatures and
HMACs "signatures".
Authors' Addresses
Michael B. Jones
Microsoft
Email: mbj@microsoft.com
URI: http://self-issued.info/
John Bradley
independent
Email: ve7jtb@ve7jtb.com
Nat Sakimura
Nomura Research Institute
Email: n-sakimura@nri.co.jp
Jones, et al. Expires July 19, 2012 [Page 27]