JSON Web Encryption (JWE)
draft-ietf-jose-json-web-encryption-02
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 7516.
|
|
|---|---|---|---|
| Authors | Michael B. Jones , Eric Rescorla , Joe Hildebrand | ||
| Last updated | 2012-05-12 | ||
| Replaces | draft-jones-json-web-encryption | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 7516 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-ietf-jose-json-web-encryption-02
JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track E. Rescorla
Expires: November 13, 2012 RTFM
J. Hildebrand
Cisco
May 12, 2012
JSON Web Encryption (JWE)
draft-ietf-jose-json-web-encryption-02
Abstract
JSON Web Encryption (JWE) is a means of representing encrypted
content using JSON data structures. Cryptographic algorithms and
identifiers used with this specification are enumerated in the
separate JSON Web Algorithms (JWA) specification. Related digital
signature and MAC capabilities are described in the separate JSON Web
Signature (JWS) 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 November 13, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. JSON Web Encryption (JWE) Overview . . . . . . . . . . . . . . 6
3.1. Example JWE with an Integrated Integrity Check . . . . . . 6
3.2. Example JWE with a Separate Integrity Check . . . . . . . 7
4. JWE Header . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Reserved Header Parameter Names . . . . . . . . . . . . . 8
4.1.1. "alg" (Algorithm) Header Parameter . . . . . . . . . . 9
4.1.2. "enc" (Encryption Method) Header Parameter . . . . . . 9
4.1.3. "int" (Integrity Algorithm) Header Parameter . . . . . 9
4.1.4. "iv" (Initialization Vector) Header Parameter . . . . 10
4.1.5. "epk" (Ephemeral Public Key) Header Parameter . . . . 10
4.1.6. "zip" (Compression Algorithm) Header Parameter . . . . 10
4.1.7. "jku" (JWK Set URL) Header Parameter . . . . . . . . . 10
4.1.8. "jwk" (JSON Web Key) Header Parameter . . . . . . . . 10
4.1.9. "x5u" (X.509 URL) Header Parameter . . . . . . . . . . 11
4.1.10. "x5t" (X.509 Certificate Thumbprint) Header
Parameter . . . . . . . . . . . . . . . . . . . . . . 11
4.1.11. "x5c" (X.509 Certificate Chain) Header Parameter . . . 11
4.1.12. "kid" (Key ID) Header Parameter . . . . . . . . . . . 12
4.1.13. "typ" (Type) Header Parameter . . . . . . . . . . . . 12
4.2. Public Header Parameter Names . . . . . . . . . . . . . . 12
4.3. Private Header Parameter Names . . . . . . . . . . . . . . 12
5. Message Encryption . . . . . . . . . . . . . . . . . . . . . . 13
6. Message Decryption . . . . . . . . . . . . . . . . . . . . . . 14
7. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . . 15
8. CMK Encryption . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Asymmetric Encryption . . . . . . . . . . . . . . . . . . 16
8.2. Symmetric Encryption . . . . . . . . . . . . . . . . . . . 16
9. Integrity Value Calculation . . . . . . . . . . . . . . . . . 16
10. Encrypting JWEs with Cryptographic Algorithms . . . . . . . . 17
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11.1. Registration of application/jwe MIME Media Type . . . . . 17
11.2. Registration of "JWE" Type Value . . . . . . . . . . . . . 18
12. Security Considerations . . . . . . . . . . . . . . . . . . . 19
13. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 19
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
14.1. Normative References . . . . . . . . . . . . . . . . . . . 19
14.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. JWE Examples . . . . . . . . . . . . . . . . . . . . 21
A.1. JWE Example using TBD Algorithm . . . . . . . . . . . . . 21
A.1.1. Encrypting . . . . . . . . . . . . . . . . . . . . . . 21
A.1.2. Decrypting . . . . . . . . . . . . . . . . . . . . . . 21
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 21
Appendix C. Document History . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
JSON Web Encryption (JWE) is a compact encryption format intended for
space constrained environments such as HTTP Authorization headers and
URI query parameters. It provides a wrapper for encrypted content
using JSON RFC 4627 [RFC4627] data structures. The JWE encryption
mechanisms are independent of the type of content being encrypted.
Cryptographic algorithms and identifiers used with this specification
are enumerated in the separate JSON Web Algorithms (JWA) [JWA]
specification. Related digital signature and MAC capabilities are
described in the separate JSON Web Signature (JWS) [JWS]
specification.
2. Terminology
JSON Web Encryption (JWE) A data structure representing an encrypted
version of a Plaintext. The structure consists of four parts: the
JWE Header, the JWE Encrypted Key, the JWE Ciphertext, and the JWE
Integrity Value.
Plaintext The bytes to be encrypted - a.k.a., the message. The
plaintext can contain an arbitrary sequence of bytes.
Ciphertext The encrypted version of the Plaintext.
Content Encryption Key (CEK) A symmetric key used to encrypt the
Plaintext for the recipient to produce the Ciphertext.
Content Integrity Key (CIK) A key used with a MAC function to ensure
the integrity of the Ciphertext and the parameters used to create
it.
Content Master Key (CMK) A key from which the CEK and CIK are
derived. When key wrapping or key encryption are employed, the
CMK is randomly generated and encrypted to the recipient as the
JWE Encrypted Key. When key agreement is employed, the CMK is the
result of the key agreement algorithm.
JWE Header A string representing a JSON object that describes the
encryption operations applied to create the JWE Encrypted Key, the
JWE Ciphertext, and the JWE Integrity Value.
JWE Encrypted Key When key wrapping or key encryption are employed,
the Content Master Key (CMK) is encrypted with the intended
recipient's key and the resulting encrypted content is recorded as
a byte array, which is referred to as the JWE Encrypted Key.
Otherwise, when key agreement is employed, the JWE Encrypted Key
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is the empty byte array.
JWE Ciphertext A byte array containing the Ciphertext.
JWE Integrity Value A byte array containing a MAC value that ensures
the integrity of the Ciphertext and the parameters used to create
it.
Encoded JWE Header Base64url encoding of the bytes of the UTF-8 RFC
3629 [RFC3629] representation of the JWE Header.
Encoded JWE Encrypted Key Base64url encoding of the JWE Encrypted
Key.
Encoded JWE Ciphertext Base64url encoding of the JWE Ciphertext.
Encoded JWE Integrity Value Base64url encoding of the JWE Integrity
Value.
Header Parameter Names The names of the members within the JWE
Header.
Header Parameter Values The values of the members within the JWE
Header.
JWE Compact Serialization A representation of the JWE as the
concatenation of the Encoded JWE Header, the Encoded JWE Encrypted
Key, the Encoded JWE Ciphertext, and the Encoded JWE Integrity
Value in that order, with the four strings being separated by
period ('.') characters.
AEAD Algorithm An Authenticated Encryption with Associated Data
(AEAD) [RFC5116] encryption algorithm is one that provides an
integrated content integrity check. AES Galois/Counter Mode (GCM)
is one such algorithm.
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 of [JWS] for notes on implementing base64url
encoding without padding.)
StringOrURI A JSON string value, with the additional requirement
that while arbitrary string values MAY be used, any value
containing a ":" character MUST be a URI as defined in RFC 3986
[RFC3986].
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3. JSON Web Encryption (JWE) Overview
JWE represents encrypted content using JSON data structures and
base64url encoding. The representation consists of four parts: the
JWE Header, the JWE Encrypted Key, the JWE Ciphertext, and the JWE
Integrity Value. In the Compact Serialization, the four parts are
base64url-encoded for transmission, and represented as the
concatenation of the encoded strings in that order, with the four
strings being separated by period ('.') characters. (A JSON
Serialization for this information is defined in the separate JSON
Web Encryption JSON Serialization (JWE-JS) [JWE-JS] specification.)
JWE utilizes encryption to ensure the confidentiality of the contents
of the Plaintext. JWE adds a content integrity check if not provided
by the underlying encryption algorithm.
3.1. Example JWE with an Integrated Integrity Check
The following example JWE Header declares that:
o the Content Master Key is encrypted to the recipient using the
RSA-PKCS1_1.5 algorithm to produce the JWE Encrypted Key,
o the Plaintext is encrypted using the AES-256-GCM algorithm to
produce the JWE Ciphertext,
o the specified 96 bit Initialization Vector with the base64url
encoding "__79_Pv6-fj39vX0" was used, and
o a JSON Web Key Set (JWK Set) representation of the public key used
to encrypt the JWE is located at
"https://example.com/public_key.jwk".
{"alg":"RSA1_5",
"enc":"A256GCM",
"iv":"__79_Pv6-fj39vX0",
"jku":"https://example.com/public_key.jwk"}
Base64url encoding the bytes of the UTF-8 representation of the JWE
Header yields this Encoded JWE Header value (with line breaks for
display purposes only):
eyJhbGciOiJSU0ExXzUiLA0KICJlbmMiOiJBMjU2R0NNIiwNCiAiaXYiOiJfXzc5
X1B2Ni1mZyIsDQogImprdSI6Imh0dHBzOi8vZXhhbXBsZS5jb20vcHVibGljX2tl
eS5qd2sifQ
TBD: Finish this example by showing generation of a Content Master
Key (CMK), saying that the CMK is used as the CEK and there is no
separate integrity check since AES GCM is an AEAD algorithm, using
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the recipient's key to encrypt the CMK to produce the JWE Encrypted
Key, using the CEK, IV, Encoded JWE Header, and Encoded JWE Encrypted
Key to encrypt the Plaintext to produce the Ciphertext and
"authentication tag" value, base64url encoding these values, and
assembling the result.
Concatenating these parts in the order
Header.EncryptedKey.Ciphertext.IntegrityValue with period characters
between the parts yields this complete JWE representation (with line
breaks for display purposes only):
eyJhbGciOiJSU0ExXzUiLA0KICJlbmMiOiJBMjU2R0NNIiwNCiAiaXYiOiJfXzc5
X1B2Ni1mZyIsDQogImprdSI6Imh0dHBzOi8vZXhhbXBsZS5jb20vcHVibGljX2tl
eS5qd2sifQ
.
TBD_encrypted_key_value_TBD
.
TBD_ciphertext_value_TBD
.
TBD_integrity_value_TBD
3.2. Example JWE with a Separate Integrity Check
The following example JWE Header declares that:
o the Content Master Key is encrypted to the recipient using the
RSA-PKCS1_1.5 algorithm to produce the JWE Encrypted Key,
o the Plaintext is encrypted using the AES-256-CBC algorithm to
produce the JWE Ciphertext,
o the JWE Integrity Value safeguarding the integrity of the
Ciphertext and the parameters used to create it was computed with
the HMAC SHA-256 algorithm,
o the specified 128 bit Initialization Vector with the base64url
encoding "AxY8DCtDaGlsbGljb3RoZQ" was used, and
o the thumbprint of the X.509 certificate that corresponds to the
key used to encrypt the JWE has the base64url encoding
"7noOPq-hJ1_hCnvWh6IeYI2w9Q0".
{"alg":"RSA1_5",
"enc":"A256CBC",
"int":"HS256",
"iv":"AxY8DCtDaGlsbGljb3RoZQ",
"x5t":"7noOPq-hJ1_hCnvWh6IeYI2w9Q0"}
Because AES CBC is not an AEAD algorithm (and so provides no
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integrated content integrity check), a separate integrity check value
is used.
Base64url encoding the bytes of the UTF-8 representation of the JWE
Header yields this Encoded JWE Header value (with line breaks for
display purposes only):
eyJhbGciOiJSU0ExXzUiLA0KICJlbmMiOiJBMjU2Q0JDIiwNCiAiaW50IjoiSFMy
NTYiLA0KICJpdiI6Ik16LW1XXzRKSGZnIiwNCiAieDV0IjoiN25vT1BxLWhKMV9o
Q252V2g2SWVZSTJ3OVEwIn0
TBD: Finish this example by showing generation of a Content Master
Key (CMK), showing the derivation of the CEK and the CIK from the
CMK, using the recipient's key to encrypt the CMK to produce the JWE
Encrypted Key, using the CEK and IV to encrypt the Plaintext to
produce the Ciphertext, showing the computation of the JWE Integrity
Value, base64url encoding these values, and assembling the result.
eyJhbGciOiJSU0ExXzUiLA0KICJlbmMiOiJBMjU2Q0JDIiwNCiAiaW50IjoiSFMy
NTYiLA0KICJpdiI6Ik16LW1XXzRKSGZnIiwNCiAieDV0IjoiN25vT1BxLWhKMV9o
Q252V2g2SWVZSTJ3OVEwIn0
.
TBD_encrypted_key_value_TBD
.
TBD_ciphertext_value_TBD
.
TBD_integrity_value_TBD
4. JWE Header
The members of the JSON object represented by the JWE Header describe
the encryption applied to the Plaintext and optionally additional
properties of the JWE. The Header Parameter Names within this object
MUST be unique; JWEs with duplicate Header Parameter Names MUST be
rejected. Implementations MUST understand the entire contents of the
header; otherwise, the JWE MUST be rejected.
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 with meanings as
defined below. All the names are short because a core goal of JWE is
for the representations to be compact.
Additional reserved header parameter names MAY be defined via the
IANA JSON Web Signature and Encryption Header Parameters registry
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[JWA]. As indicated by the common registry, JWSs and JWEs share a
common header parameter space; when a parameter is used by both
specifications, its usage must be compatible between the
specifications.
4.1.1. "alg" (Algorithm) Header Parameter
The "alg" (algorithm) header parameter identifies the cryptographic
algorithm used to secure the JWE Encrypted Key. A list of defined
"alg" values for use with JWE is presented in Section 4.1 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 intended recipient. The "alg" value is
case sensitive. Its value MUST be a string containing a StringOrURI
value. This header parameter is REQUIRED.
"alg" values SHOULD either be defined in the IANA JSON Web Signature
and Encryption Algorithms registry [JWA] or be a URI that contains a
collision resistant namespace.
4.1.2. "enc" (Encryption Method) Header Parameter
The "enc" (encryption method) header parameter identifies the
symmetric encryption algorithm used to secure the Ciphertext. A list
of defined "enc" values is presented in Section 4.2 of the JSON Web
Algorithms (JWA) [JWA] specification. The processing of the "enc"
(encryption method) header parameter requires that the value MUST be
one that is supported. The "enc" value is case sensitive. Its value
MUST be a string containing a StringOrURI value. This header
parameter is REQUIRED.
"enc" values SHOULD either be defined in the IANA JSON Web Signature
and Encryption Algorithms registry [JWA] or be a URI that contains a
collision resistant namespace.
4.1.3. "int" (Integrity Algorithm) Header Parameter
The "int" (integrity algorithm) header parameter identifies the
cryptographic algorithm used to safeguard the integrity of the
Ciphertext and the parameters used to create it. A list of defined
"int" values is presented in Section 4.3 of the JSON Web Algorithms
(JWA) [JWA] specification. The "int" parameter uses the MAC subset
of the algorithm values used by the JWS "alg" parameter. The "int"
value is case sensitive. Its value MUST be a string containing a
StringOrURI value. This header parameter is REQUIRED when an AEAD
algorithm is not used to encrypt the Plaintext and MUST NOT be
present when an AEAD algorithm is used.
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"int" values SHOULD either be defined in the IANA JSON Web Signature
and Encryption Algorithms registry [JWA] or be a URI that contains a
collision resistant namespace.
4.1.4. "iv" (Initialization Vector) Header Parameter
The "iv" (initialization vector) value for algorithms requiring it,
represented as a base64url encoded string. This header parameter is
OPTIONAL.
4.1.5. "epk" (Ephemeral Public Key) Header Parameter
The "epk" (ephemeral public key) value created by the originator for
the use in ECDH-ES RFC 6090 [RFC6090] encryption. This key is
represented as a JSON Web Key [JWK] value, containing "crv" (curve),
"x", and "y" members. The inclusion of the JWK "alg" (algorithm)
member is OPTIONAL. This header parameter is OPTIONAL.
4.1.6. "zip" (Compression Algorithm) Header Parameter
The "zip" (compression algorithm) applied to the Plaintext before
encryption, if any. If present, the value of the "zip" header
parameter MUST be the case sensitive string "DEF". Compression is
performed with the DEFLATE [RFC1951] algorithm. If no "zip"
parameter is present, no compression is applied to the Plaintext
before encryption. This header parameter is OPTIONAL.
4.1.7. "jku" (JWK Set URL) Header Parameter
The "jku" (JWK Set 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 used to encrypt the JWE. The keys MUST
be encoded as a JSON Web Key Set (JWK Set) as defined 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]; the identity of the server MUST be validated, as per
Section 3.1 of HTTP Over TLS [RFC2818]. This header parameter is
OPTIONAL.
4.1.8. "jwk" (JSON Web Key) Header Parameter
The "jwk" (JSON Web Key) header parameter is a public key that
corresponds to the key used to encrypt the JWE. This key is
represented as a JSON Web Key [JWK]. This header parameter is
OPTIONAL.
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4.1.9. "x5u" (X.509 URL) Header Parameter
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 encrypt the JWE. 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 certificate containing the
public key of the entity that encrypted the JWE MUST be the first
certificate. This MAY be followed by additional certificates, with
each subsequent certificate being the one used to certify the
previous one. 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]; the identity of
the server MUST be validated, as per Section 3.1 of HTTP Over TLS
[RFC2818]. This header parameter is OPTIONAL.
4.1.10. "x5t" (X.509 Certificate Thumbprint) Header Parameter
The "x5t" (X.509 Certificate Thumbprint) header parameter provides a
base64url encoded SHA-1 thumbprint (a.k.a. digest) of the DER
encoding of the X.509 certificate corresponding to the key used to
encrypt the JWE. This header parameter is OPTIONAL.
If, in the future, certificate thumbprints need to be computed using
hash functions other than SHA-1, it is suggested that additional
related header parameters be defined for that purpose. For example,
it is suggested that a new "x5t#S256" (X.509 Certificate Thumbprint
using SHA-256) header parameter could be defined by registering it in
the IANA JSON Web Signature and Encryption Header Parameters registry
[JWA].
4.1.11. "x5c" (X.509 Certificate Chain) Header Parameter
The "x5c" (X.509 Certificate Chain) header parameter contains the
X.509 public key certificate or certificate chain corresponding to
the key used to encrypt the JWE. The certificate or certificate
chain is represented as an array of certificate values. Each value
is a base64-encoded (not base64url encoded) DER/BER PKIX certificate
value. The certificate containing the public key of the entity that
encrypted the JWE MUST be the first certificate. This MAY be
followed by additional certificates, with each subsequent certificate
being the one used to certify the previous one. The recipient MUST
verify the certificate chain according to [RFC5280] and reject the
JWE if any validation failure occurs. This header parameter is
OPTIONAL.
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4.1.12. "kid" (Key ID) Header Parameter
The "kid" (key ID) header parameter is a hint indicating which key
was used to encrypt the JWE. This allows originators to explicitly
signal a change of key to recipients. Should the recipient be unable
to locate a key corresponding to the "kid" value, they SHOULD treat
that condition as an error. The interpretation of the contents of
the "kid" parameter is unspecified. Its value MUST be a string.
This header parameter is OPTIONAL.
4.1.13. "typ" (Type) Header Parameter
The "typ" (type) header parameter is used to declare the type of the
encrypted content. The type value "JWE" MAY be used to indicate that
the encrypted content is a JWE. The "typ" value is case sensitive.
Its value MUST be a string. This header parameter is OPTIONAL.
MIME Media Type RFC 2045 [RFC2045] values MAY be used as "typ"
values.
"typ" values SHOULD either be defined in the IANA JSON Web Signature
and Encryption "typ" Values registry [JWA] or be a URI that contains
a collision resistant namespace.
4.2. Public Header Parameter Names
Additional header parameter names can be defined by those using JWEs.
However, in order to prevent collisions, any new header parameter
name SHOULD either be defined in the IANA JSON Web Signature and
Encryption Header Parameters registry [JWA] or be 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 JWEs.
4.3. Private Header Parameter Names
A producer and consumer of a JWE 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.
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5. Message Encryption
The message encryption process is as follows. The order of the steps
is not significant in cases where there are no dependencies between
the inputs and outputs of the steps.
1. When key wrapping or key encryption are employed, generate a
random Content Master Key (CMK). See RFC 4086 [RFC4086] for
considerations on generating random values. Otherwise, when key
agreement is employed, use the key agreement algorithm to
compute the value of the Content Master Key (CMK). The CMK MUST
have a length equal to that of the larger of the required
encryption and integrity keys.
2. When key wrapping or key encryption are employed, encrypt the
CMK for the recipient (see Section 8) and let the result be the
JWE Encrypted Key. Otherwise, when key agreement is employed,
let the JWE Encrypted Key be an empty byte array.
3. Base64url encode the JWE Encrypted Key to create the Encoded JWE
Encrypted Key.
4. Generate a random Initialization Vector (IV) of the correct size
for the algorithm (if required for the algorithm).
5. If not using an AEAD algorithm, run the key derivation algorithm
(see Section 7) to generate the Content Encryption Key (CEK) and
the Content Integrity Key (CIK); otherwise (when using an AEAD
algorithm), set the CEK to be the CMK.
6. Compress the Plaintext if a "zip" parameter was included.
7. Serialize the (compressed) Plaintext into a byte sequence M.
8. Encrypt M using the CEK and IV to form the byte sequence C. If
an AEAD algorithm is used, use the concatenation of the Encoded
JWE Header, a period ('.') character, and the Encoded JWE
Encrypted Key as the "additional authenticated data" parameter
value for the encryption.
9. Base64url encode C to create the Encoded JWE Ciphertext.
10. Create a JWE Header containing the encryption parameters used.
Note that white space is explicitly allowed in the
representation and no canonicalization need be performed before
encoding.
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11. Base64url encode the bytes of the UTF-8 representation of the
JWE Header to create the Encoded JWE Header.
12. If not using an AEAD algorithm, run the integrity algorithm (see
Section 9) using the CIK to compute the JWE Integrity Value;
otherwise (when using an AEAD algorithm), set the JWE Integrity
Value to be the "authentication tag" value produced by the AEAD
algorithm.
13. Base64url encode the JWE Integrity Value to create the Encoded
JWE Integrity Value.
14. The four encoded parts, taken together, are the result. The
Compact Serialization of this result is the concatenation of the
Encoded JWE Header, the Encoded JWE Encrypted Key, the Encoded
JWE Ciphertext, and the Encoded JWE Integrity Value in that
order, with the four strings being separated by period ('.')
characters.
6. Message Decryption
The message decryption process is the reverse of the encryption
process. The order of the steps is not significant in cases where
there are no dependencies between the inputs and outputs of the
steps. If any of these steps fails, the JWE MUST be rejected.
1. Parse the four parts of the input (which are separated by period
characters when using the JWE Compact Serialization) into the
Encoded JWE Header, the Encoded JWE Encrypted Key, the Encoded
JWE Ciphertext, and the Encoded JWE Integrity Value.
2. The Encoded JWE Header, the Encoded JWE Encrypted Key, the
Encoded JWE Ciphertext, and the Encoded JWE Integrity Value MUST
be successfully base64url decoded following the restriction that
no padding characters have been used.
3. The resulting JWE Header MUST be completely valid JSON syntax
conforming to RFC 4627 [RFC4627].
4. The resulting JWE Header MUST be validated to only include
parameters and values whose syntax and semantics are both
understood and supported.
5. Verify that the JWE Header references a key known to the
recipient.
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6. When key wrapping or key encryption are employed, decrypt the
JWE Encrypted Key to produce the Content Master Key (CMK).
Otherwise, when key agreement is employed, use the key agreement
algorithm to compute the value of the Content Master Key (CMK).
The CMK MUST have a length equal to that of the larger of the
required encryption and integrity keys.
7. If not using an AEAD algorithm, run the key derivation algorithm
(see Section 7) to generate the Content Encryption Key (CEK) and
the Content Integrity Key (CIK); otherwise (when using an AEAD
algorithm), set the CEK to be the CMK.
8. Decrypt the binary representation of the JWE Ciphertext using
the CEK and IV. If an AEAD algorithm is used, use the
concatenation of the Encoded JWE Header, a period ('.')
character, and the Encoded JWE Encrypted Key as the "additional
authenticated data" parameter value for the decryption.
9. If not using an AEAD algorithm, run the integrity algorithm (see
Section 9) using the CIK to compute an integrity value for the
input received. This computed value MUST match the received JWE
Integrity Value; otherwise (when using an AEAD algorithm), the
received JWE Integrity Value MUST match the "authentication tag"
value produced by the AEAD algorithm.
10. Uncompress the result of the previous step, if a "zip" parameter
was included.
11. Output the resulting Plaintext.
7. Key Derivation
The key derivation process converts the CMK into a CEK and a CIK. It
assumes as a primitive a Key Derivation Function (KDF) which
notionally takes three arguments:
MasterKey: The master key used to compute the individual use keys
Label: The use key label, used to differentiate individual use keys
Length: The desired length of the use key
The only KDF used in this document is the Concat KDF, as defined in
Section 5.8.1 of [NIST.800-56A], where the Digest Method is SHA-256,
the SuppPubInfo parameter is the Label, and the remaining OtherInfo
parameters are the empty bit string.
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To compute the CEK from the CMK, the ASCII label "Encryption" ([69,
110, 99, 114, 121, 112, 116, 105, 111, 110]) is used. Use the key
size for the "enc" algorithm as the CEK desired key length.
To compute the CIK from the CMK, the ASCII label "Integrity" ([73,
110, 116, 101, 103, 114, 105, 116, 121]) is used. Use the minimum
key size for the "int" algorithm (for instance, 256 bits for "HS256")
as the CIK desired key length.
8. CMK Encryption
JWE supports two forms of CMK encryption:
o Asymmetric encryption under the recipient's public key.
o Symmetric encryption under a shared key.
8.1. Asymmetric Encryption
In the asymmetric encryption mode, the CMK is encrypted under the
recipient's public key. The asymmetric encryption modes defined for
use with this in this specification are listed in Section 4.1 of the
JSON Web Algorithms (JWA) [JWA] specification.
8.2. Symmetric Encryption
In the symmetric encryption mode, the CMK is encrypted under a
symmetric key shared between the sender and receiver. The symmetric
encryption modes defined for use with this in this specification are
listed in Section 4.1 of the JSON Web Algorithms (JWA) [JWA]
specification.
9. Integrity Value Calculation
When a non-AEAD algorithm is used (an algorithm without an integrated
content check), JWE adds an explicit integrity check value to the
representation. This value is computed in the manner described in
the JSON Web Signature (JWS) [JWS] specification, with these
modifications:
o The algorithm used is taken from the "int" (integrity algorithm)
header parameter rather than the "alg" header parameter.
o The algorithm MUST be a MAC algorithm (normally HMAC SHA-256).
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o The JWS Secured Input used is the concatenation of the Encoded JWE
Header, a period ('.') character, the Encoded JWE Encrypted Key, a
period ('.') character, and the Encoded JWE Ciphertext.
o The CIK is used as the MAC key.
The computed JWS Signature value is the resulting integrity value.
10. Encrypting JWEs with Cryptographic Algorithms
JWE uses cryptographic algorithms to encrypt the Plaintext and the
Content Encryption Key (CMK) and to provide integrity protection for
the JWE Header, JWE Encrypted Key, and JWE Ciphertext. The JSON Web
Algorithms (JWA) [JWA] specification enumerates a set of
cryptographic algorithms and identifiers to be used with this
specification. Specifically, Section 4.1 enumerates a set of "alg"
(algorithm) header parameter values, Section 4.2 enumerates a set of
"enc" (encryption method) header parameter values, and Section 4.3
enumerates a set of "int" (integrity 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 encryption 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.
11. IANA Considerations
11.1. Registration of application/jwe MIME Media Type
This specification registers the "application/jwe" MIME Media Type
RFC 2045 [RFC2045].
Type name:
application
Subtype name:
jwe
Required parameters:
n/a
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Optional parameters:
n/a
Encoding considerations:
n/a
Security considerations:
See the Security Considerations section of this document
Interoperability considerations:
n/a
Published specification:
[[ this document ]]
Applications that use this media type:
OpenID Connect
Additional information:
Magic number(s): n/a
File extension(s): n/a
Macintosh file type code(s): n/a
Person & email address to contact for further information:
Michael B. Jones
mbj@microsoft.com
Intended usage:
COMMON
Restrictions on usage:
none
Author:
Michael B. Jones
mbj@microsoft.com
Change controller:
IETF
11.2. Registration of "JWE" Type Value
This specification registers the following "typ" header parameter
value in the JSON Web Signature and Encryption "typ" Values registry
established by the JSON Web Algorithms (JWA) [JWA] specification:
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"typ" header parameter value:
"JWE"
Abbreviation for MIME type:
application/jwe
Change controller:
IETF
Description:
[[ this document ]]
12. Security Considerations
All the security considerations in the JWS specification also apply
to this specification, other than those that are signature specific.
Likewise, all the security considerations in XML Encryption 1.1
[W3C.CR-xmlenc-core1-20120313] also apply to JWE, other than those
that are XML specific.
13. Open Issues and Things To Be Done (TBD)
The following items remain to be done in this draft:
o Add examples, including a KDF and a key agreement example.
14. References
14.1. Normative References
[JWA] Jones, M., "JSON Web Algorithms (JWA)", May 2012.
[JWK] Jones, M., "JSON Web Key (JWK)", May 2012.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", May 2012.
[NIST.800-56A]
National Institute of Standards and Technology (NIST),
"Recommendation for Pair-Wise Key Establishment Schemes
Using Discrete Logarithm Cryptography (Revised)", NIST PUB
800-56A, March 2007.
[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication
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Procedures", RFC 1421, February 1993.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
[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.
[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.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 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.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 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.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, February 2011.
14.2. Informative References
[I-D.rescorla-jsms]
Rescorla, E. and J. Hildebrand, "JavaScript Message
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Security Format", draft-rescorla-jsms-00 (work in
progress), March 2011.
[JSE] Bradley, J. and N. Sakimura (editor), "JSON Simple
Encryption", September 2010.
[JWE-JS] Jones, M., "JSON Web Encryption JSON Serialization
(JWE-JS)", March 2012.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[W3C.CR-xmlenc-core1-20120313]
Eastlake, D., Reagle, J., Roessler, T., and F. Hirsch,
"XML Encryption Syntax and Processing Version 1.1", World
Wide Web Consortium CR CR-xmlenc-core1-20120313,
March 2012,
<http://www.w3.org/TR/2012/CR-xmlenc-core1-20120313>.
Appendix A. JWE Examples
This section provides several examples of JWEs.
A.1. JWE Example using TBD Algorithm
A.1.1. Encrypting
TBD: Demonstrate encryption steps with this algorithm
A.1.2. Decrypting
TBD: Demonstrate decryption steps with this algorithm
Appendix B. Acknowledgements
Solutions for encrypting JSON content were also explored by JSON
Simple Encryption [JSE] and JavaScript Message Security Format
[I-D.rescorla-jsms], both of which significantly influenced this
draft. This draft attempts to explicitly reuse as many of the
relevant concepts from XML Encryption 1.1
[W3C.CR-xmlenc-core1-20120313] and RFC 5652 [RFC5652] as possible,
while utilizing simple compact JSON-based data structures.
Special thanks are due to John Bradley and Nat Sakimura for the
discussions that helped inform the content of this specification and
to Eric Rescorla and Joe Hildebrand for allowing the reuse of text
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from [I-D.rescorla-jsms] in this document.
Appendix C. Document History
-02
o When using AEAD algorithms (such as AES GCM), use the "additional
authenticated data" parameter to provide integrity for the header,
encrypted key, and ciphertext and use the resulting
"authentication tag" value as the JWE Integrity Value.
o Defined KDF output key sizes.
o Generalized text to allow key agreement to be employed as an
alternative to key wrapping or key encryption.
o Changed compression algorithm from gzip to DEFLATE.
o Clarified that it is an error when a "kid" value is included and
no matching key is found.
o Clarified that JWEs with duplicate Header Parameter Names MUST be
rejected.
o Clarified the relationship between "typ" header parameter values
and MIME types.
o Registered application/jwe MIME type and "JWE" typ header
parameter value.
o Simplified JWK terminology to get replace the "JWK Key Object" and
"JWK Container Object" terms with simply "JSON Web Key (JWK)" and
"JSON Web Key Set (JWK Set)" and to eliminate potential confusion
between single keys and sets of keys. As part of this change, the
header parameter name for a public key value was changed from
"jpk" (JSON Public Key) to "jwk" (JSON Web Key).
o Added suggestion on defining additional header parameters such as
"x5t#S256" in the future for certificate thumbprints using hash
algorithms other than SHA-1.
o Specify RFC 2818 server identity validation, rather than RFC 6125
(paralleling the same decision in the OAuth specs).
o Generalized language to refer to Message Authentication Codes
(MACs) rather than Hash-based Message Authentication Codes (HMACs)
unless in a context specific to HMAC algorithms.
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o Reformatted to give each header parameter its own section heading.
-01
o Added an integrity check for non-AEAD algorithms.
o Added "jpk" and "x5c" header parameters for including JWK public
keys and X.509 certificate chains directly in the header.
o Clarified that this specification is defining the JWE Compact
Serialization. Referenced the new JWE-JS spec, which defines the
JWE JSON Serialization.
o Added text "New header parameters should be introduced sparingly
since an implementation that does not understand a parameter MUST
reject the JWE".
o Clarified that the order of the encryption and decryption steps is
not significant in cases where there are no dependencies between
the inputs and outputs of the steps.
o Made other editorial improvements suggested by JOSE working group
participants.
-00
o Created the initial IETF draft based upon
draft-jones-json-web-encryption-02 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/
Eric Rescorla
RTFM, Inc.
Email: ekr@rtfm.com
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Joe Hildebrand
Cisco Systems, Inc.
Email: jhildebr@cisco.com
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