JOSE Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track E. Rescorla
Expires: September 13, 2012 RTFM, Inc.
J. Hildebrand
Cisco Systems, Inc.
March 12, 2012
JSON Web Encryption (JWE)
draft-ietf-jose-json-web-encryption-01
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 HMAC 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 September 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. JSON Web Encryption (JWE) Overview . . . . . . . . . . . . . . 4
3.1. Example JWE with an Integrated Integrity Check . . . . . . 5
3.2. Example JWE with a Separate Integrity Check . . . . . . . 6
4. JWE Header . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Reserved Header Parameter Names . . . . . . . . . . . . . 7
4.2. Public Header Parameter Names . . . . . . . . . . . . . . 14
4.3. Private Header Parameter Names . . . . . . . . . . . . . . 14
5. Message Encryption . . . . . . . . . . . . . . . . . . . . . . 14
6. Message Decryption . . . . . . . . . . . . . . . . . . . . . . 16
7. Key Derivation . . . . . . . . . . . . . . . . . . . . . . . . 17
8. CMK Encryption . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Asymmetric Encryption . . . . . . . . . . . . . . . . . . 17
8.2. Symmetric Encryption . . . . . . . . . . . . . . . . . . . 18
9. Integrity Value Calculation . . . . . . . . . . . . . . . . . 18
10. Encrypting JWEs with Cryptographic Algorithms . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. Security Considerations . . . . . . . . . . . . . . . . . . . 19
12.1. Unicode Comparison Security Issues . . . . . . . . . . . . 19
13. Open Issues and Things To Be Done (TBD) . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
14.1. Normative References . . . . . . . . . . . . . . . . . . . 21
14.2. Informative References . . . . . . . . . . . . . . . . . . 22
Appendix A. JWE Examples . . . . . . . . . . . . . . . . . . . . 23
A.1. JWE Example using TBD Algorithm . . . . . . . . . . . . . 23
A.1.1. Encrypting . . . . . . . . . . . . . . . . . . . . . . 23
A.1.2. Decrypting . . . . . . . . . . . . . . . . . . . . . . 23
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Appendix C. Document History . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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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 HMAC 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.
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 an HMAC function to
ensure the integrity of the Ciphertext and the parameters used to
create it.
Content Master Key (CMK) A randomly generated key from which the CEK
and CIK are derived, which is encrypted to the recipient as the
JWE Encrypted Key.
JWE Header A string representing a JSON object that describes the
encryption operations applied to create the JWE Encrypted Key and
the JWE Ciphertext.
JWE Encrypted Key The Content Encryption Key (CEK) 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.
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JWE Ciphertext A byte array containing the Ciphertext.
JWE Integrity Value A byte array containing a HMAC 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.)
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
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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 64-bit Initialization Vector with the base64url
encoding "__79_Pv6-fg" was used, and
o a JSON Web Key (JWK) 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-fg",
"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
the CEK to encrypt the Plaintext to produce the Ciphertext, using the
recipient's key to encrypt the CMK to produce the JWE Encrypted Key,
base64url encoding these values, and assembling the result.
Concatenating these parts in the order
Header.EncryptedKey.Ciphertext.IntegrityValue with period characters
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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
.
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 64-bit Initialization Vector with the base64url
encoding "Mz-mW_4JHfg" 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":"Mz-mW_4JHfg",
"x5t":"7noOPq-hJ1_hCnvWh6IeYI2w9Q0"}
Because AES CBC is not an AEAD algorithm (and so provides no
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
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TBD: Finish this example by showing generation of a Content Master
Key (CMK), showing the derivation of the CEK and the CEK from the
CMK, using the CEK to encrypt the Plaintext to produce the
Ciphertext, using the recipient's key to encrypt the CMK to produce
the JWE Encrypted Key, 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. Implementations MUST understand the entire contents
of the header; otherwise, the JWE MUST be rejected.
4.1. Reserved Header Parameter Names
The following header parameter names are reserved. All the names are
short because a core goal of JWE 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 JWE |
| | | | Encrypted Key. A list of |
| | | | defined encryption "alg" |
| | | | values is presented in |
| | | | Section 4, Table 2 of the |
| | | | JSON Web Algorithms (JWA) |
| | | | [JWA] specification. The |
| | | | processing of the "alg" |
| | | | (algorithm) 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. This header |
| | | | parameter is REQUIRED. |
| enc | string | StringOrURI | 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, Table 3 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. This |
| | | | header parameter is |
| | | | REQUIRED. |
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| int | string | StringOrURI | 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. The "int" |
| | | | parameter uses the same |
| | | | values as the JWS "alg" |
| | | | parameter; a list of |
| | | | defined JWS "alg" values is |
| | | | presented in Section 3, |
| | | | Table 1 of the JSON Web |
| | | | Algorithms (JWA) [JWA] |
| | | | specification. 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. |
| iv | string | String | Initialization Vector |
| | | | ("iv") value for algorithms |
| | | | requiring it, represented |
| | | | as a base64url encoded |
| | | | string. This header |
| | | | parameter is OPTIONAL. |
| epk | object | JWK Key Object | Ephemeral Public Key |
| | | | ("epk") value created by |
| | | | the originator for the use |
| | | | in ECDH-ES RFC 6090 |
| | | | [RFC6090] encryption. This |
| | | | key is represented in the |
| | | | same manner as a JSON Web |
| | | | Key [JWK] JWK Key Object |
| | | | value, containing "crv" |
| | | | (curve), "x", and "y" |
| | | | members. The inclusion of |
| | | | the JWK Key Object "alg" |
| | | | (algorithm) member is |
| | | | OPTIONAL. This header |
| | | | parameter is OPTIONAL. |
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| zip | string | String | Compression algorithm |
| | | | ("zip") applied to the |
| | | | Plaintext before |
| | | | encryption, if any. This |
| | | | specification defines the |
| | | | value "GZIP" to refer to |
| | | | the encoding format |
| | | | produced by the file |
| | | | compression program "gzip" |
| | | | (GNU zip) as described in |
| | | | [RFC1952]; this format is a |
| | | | Lempel-Ziv coding (LZ77) |
| | | | with a 32 bit CRC. If no |
| | | | "zip" parameter is present, |
| | | | or its value is "none", no |
| | | | compression is applied to |
| | | | the Plaintext before |
| | | | encryption. The "zip" |
| | | | value is case sensitive. |
| | | | This header parameter is |
| | | | OPTIONAL. |
| 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 |
| | | | encrypt the JWE. 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. |
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| kid | string | String | 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. The |
| | | | interpretation of the |
| | | | contents of the "kid" |
| | | | parameter is unspecified. |
| | | | This header parameter is |
| | | | OPTIONAL. |
| jpk | object | JWK Key Object | The "jpk" (JSON Public Key) |
| | | | header parameter is a |
| | | | public key that corresponds |
| | | | to the key that was used to |
| | | | encrypt the JWE. This key |
| | | | is represented in the same |
| | | | manner as a JSON Web Key |
| | | | [JWK] JWK Key Object value. |
| | | | 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 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 encrypting |
| | | | 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] 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 the |
| | | | X.509 certificate that |
| | | | corresponds to the key that |
| | | | was used to encrypt the |
| | | | JWE. This header parameter |
| | | | is OPTIONAL. |
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| x5c | array | ArrayOfStrings | 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 encrypting |
| | | | 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. |
| typ | string | String | The "typ" (type) header |
| | | | parameter is used to |
| | | | declare the type of the |
| | | | encrypted content. The |
| | | | "typ" value is case |
| | | | sensitive. This header |
| | | | parameter is OPTIONAL. |
+-----------+--------+----------------+-----------------------------+
Table 1: Reserved Header Parameter Definitions
Additional reserved header parameter names MAY be defined via the
IANA JSON Web Encryption Header Parameters registry, as per
Section 11. The syntax values used above are defined as follows:
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+----------------+--------------------------------------------------+
| Syntax Name | Syntax Definition |
+----------------+--------------------------------------------------+
| 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]. |
| ArrayOfStrings | An array of string values. |
+----------------+--------------------------------------------------+
Table 2: Header Parameter Syntax Definitions
4.2. Public Header Parameter Names
Additional header parameter names can be defined by those using JWE.
However, in order to prevent collisions, any new header parameter
name or algorithm value SHOULD either be defined in the IANA JSON Web
Encryption 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 since an
implementation that does not understand a parameter MUST reject the
JWE.
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.
New header parameters should be introduced sparingly, as they can
result in non-interoperable JWEs.
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. Generate a random Content Master Key (CMK). The CMK MUST have a
length at least equal to that of the larger of the required
encryption or integrity keys and MUST be generated randomly.
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See RFC 4086 [RFC4086] for considerations on generating random
values.
2. Encrypt the CMK for the recipient (see Section 8) and let the
result be the JWE Encrypted Key.
3. Base64url encode the JWE Encrypted Key to create the Encoded JWE
Encrypted Key.
4. Generate a random Initialization Vector (IV) (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 bitstring M.
8. Encrypt M using the CEK and IV to form the bitstring C.
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.
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 empty byte string.
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.
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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.
6. Decrypt the JWE Encrypted Key to produce the Content Master Key
(CMK).
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. 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 be empty.
9. Decrypt the binary representation of the JWE Ciphertext using
the CEK.
10. Remove the Initialization Vector (IV) value from the decrypted
result (if an IV was used).
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11. Uncompress the result of the previous step, if a "zip" parameter
was included.
12. 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 length of the desired use key
The only KDF used in this document is the Concat KDF, as defined in
[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.
To compute the CEK from the CMK, the ASCII label "Encryption" is
used.
To compute the CIK from the CMK, the ASCII label "Integrity" is used.
When AEAD algorithms are used the KDF element MUST NOT be present.
When they are not used, it MUST be present.
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, Table 2
of the JSON Web Algorithms (JWA) [JWA] specification.
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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, Table 2 of the JSON Web Algorithms (JWA) [JWA]
specification. For GCM, the random 64-bit IV is prepended to the
ciphertext.
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 an HMAC algorithm (normally HMAC SHA-256).
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 HMAC key.
The computed JWS Signature value is the resulting integrity value.
10. Encrypting JWEs with Cryptographic Algorithms
JWE uses cryptographic algorithms to encrypt the Content Encryption
Key (CMK) and the Plaintext. The JSON Web Algorithms (JWA) [JWA]
specification enumerates a set of cryptographic algorithms and
identifiers to be used with this specification. Specifically,
Section 4, Table 2 enumerates a set of "alg" (algorithm) header
parameter values and Section 4, Table 3 enumerates a set of "enc"
(encryption method) 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.
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11. IANA Considerations
This specification calls for:
o A new IANA registry entitled "JSON Web Encryption Header
Parameters" for reserved header parameter names is defined in
Section 4.1. Inclusion in the registry is RFC Required in the RFC
5226 [RFC5226] sense for reserved JWE 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.
12. 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: We need a section on generating randomness in browsers - it's
easy to screw up.
When utilizing TLS to retrieve information, the authority providing
the resource MUST be authenticated and the information retrieved MUST
be free from modification.
12.1. Unicode Comparison Security Issues
Header parameter names in JWEs 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
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being equal ("enc", "\u0065nc"), whereas these must all compare as
being not equal to the first set or to each other ("ENC", "Enc",
"en\u0043").
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, JWE
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.
13. Open Issues and Things To Be Done (TBD)
The following items remain to be done in this draft:
o EDITORIAL: Give each header parameter definition its own section.
This will let them appear in the index, will give space for
examples when needed, and will get rid of the way-too-cramped
tables.
o Consider adding the DEFLATE compression algorithm (which omits the
ZLIB header and checksum fields) and so produces smaller results
than "GZIP".
o Provide a more robust description of the use of the Initialization
Vector (IV), including listing which algorithms require an IV.
(This list may belong in the JWA spec.) The current statement
"For GCM, the random 64-bit IV is prepended to the ciphertext" in
the Symmetric Encryption section is almost certainly out of place
and insufficiently general.
o Finish the Security Considerations section.
o Consider which of the open issues from the JWS and JWT specs also
apply here.
o Should the JWE Encrypted Key be moved to the header (which would
add about 20 bytes to every JWE) or left in a separate period-
separated segment to prevent double base64 encoding?
14. References
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14.1. Normative References
[JWA] Jones, M., "JSON Web Algorithms (JWA)", January 2012.
[JWK] Jones, M., "JSON Web Key (JWK)", March 2012.
[JWS] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", January 2012.
[NIST-800-38D]
National Institute of Standards and Technology (NIST),
"Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC", NIST PUB 800-38D,
December 2001.
[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
Procedures", RFC 1421, February 1993.
[RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
Randers-Pehrson, "GZIP file format specification version
4.3", RFC 1952, May 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
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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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
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.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, February 2011.
[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.
14.2. Informative References
[I-D.rescorla-jsms]
Rescorla, E. and J. Hildebrand, "JavaScript Message
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-core1-20110303]
Hirsch, F., Roessler, T., Reagle, J., and D. Eastlake,
"XML Encryption Syntax and Processing Version 1.1", World
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Wide Web Consortium CR CR-xmlenc-core1-20110303,
March 2011,
<http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303>.
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-core1-20110303] 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
from [I-D.rescorla-jsms] in this document.
Appendix C. Document History
-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.
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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
Joe Hildebrand
Cisco Systems, Inc.
Email: jhildebr@cisco.com
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