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Versions: 00 01 02 draft-ietf-jose-json-web-encryption

Network Working Group                                           M. Jones
Internet-Draft                                                 Microsoft
Intended status: Standards Track                             E. Rescorla
Expires: May 2, 2012                                          RTFM, Inc.
                                                           J. Hildebrand
                                                     Cisco Systems, Inc.
                                                        October 30, 2011


                       JSON Web Encryption (JWE)
                   draft-jones-json-web-encryption-01

Abstract

   JSON Web Encryption (JWE) is a means of representing encrypted
   content using JSON data structures.  Related signature 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 May 2, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (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  . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  JWE Header . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     4.1.  Reserved Header Parameter Names  . . . . . . . . . . . . .  5
     4.2.  Public Header Parameter Names  . . . . . . . . . . . . . . 10
     4.3.  Private Header Parameter Names . . . . . . . . . . . . . . 10
   5.  Message Encryption . . . . . . . . . . . . . . . . . . . . . . 10
   6.  Message Decryption . . . . . . . . . . . . . . . . . . . . . . 11
   7.  CEK Encryption . . . . . . . . . . . . . . . . . . . . . . . . 12
     7.1.  Asymmetric Encryption  . . . . . . . . . . . . . . . . . . 12
     7.2.  Symmetric Encryption . . . . . . . . . . . . . . . . . . . 12
   8.  Composition  . . . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Encrypting JWEs with Cryptographic Algorithms  . . . . . . . . 12
     9.1.  Encrypting a JWE with TBD  . . . . . . . . . . . . . . . . 14
     9.2.  Additional Algorithms  . . . . . . . . . . . . . . . . . . 14
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
     11.1. Unicode Comparison Security Issues . . . . . . . . . . . . 15
   12. Open Issues and Things To Be Done (TBD)  . . . . . . . . . . . 16
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 17
     13.2. Informative References . . . . . . . . . . . . . . . . . . 19
   Appendix A.  JWE Examples  . . . . . . . . . . . . . . . . . . . . 20
     A.1.  JWE Example using TBD Algorithm  . . . . . . . . . . . . . 20
       A.1.1.  Encrypting . . . . . . . . . . . . . . . . . . . . . . 20
       A.1.2.  Decrypting . . . . . . . . . . . . . . . . . . . . . . 20
   Appendix B.  Algorithm Identifier Cross-Reference  . . . . . . . . 20
   Appendix C.  Acknowledgements  . . . . . . . . . . . . . . . . . . 23
   Appendix D.  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.  A
   related signature capability is described in a 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 three parts:
      the JWE Header, the JWE Encrypted Key, and the JWE Ciphertext.

   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 generated to encrypt
      the Plaintext for the recipient to produce the Ciphertext, which
      is encrypted to the recipient as the JWE Encrypted Key.

   JWE Header  A string containing 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.

   JWE Ciphertext  A byte array containing the Ciphertext.

   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.

   Header Parameter Names  The names of the members within the JWE
      Header.





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   Header Parameter Values  The values of the members within the JWE
      Header.

   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 C 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 three parts: the
   JWE Header, the JWE Encrypted Key, and the JWE Ciphertext.  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, as is done when used in JSON Web Tokens (JWTs) [JWT].

   JWE utilizes encryption to ensure the confidentiality of the contents
   of the Plaintext.  JWE does not add a content integrity check if not
   provided by the underlying encryption algorithm.  If such a check is
   needed, an algorithm providing it such as AES-GCM [NIST-800-38D] can
   be used, or alternatively, it can be provided through composition by
   encrypting a representation of the signed content.

3.1.  Example JWE

   The following example JWE Header declares that:

   o  the Content Encryption 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  the thumbprint of the X.509 certificate that corresponds to the
      key used to encrypt the JWE has the base64url encoding
      "7noOPq-hJ1_hCnvWh6IeYI2w9Q0".







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   {"alg":"RSA1_5",
    "enc":"A256GCM",
    "iv":"__79_Pv6-fg",
    "x5t":"7noOPq-hJ1_hCnvWh6IeYI2w9Q0"}

   Base64url encoding the bytes of the UTF-8 representation of the JWE
   Header yields this Encoded JWE Header value:
   TBD

   TBD: Finish this example by showing generation of a Content
   Encryption Key (CEK), using the CEK to encrypt the Plaintext to
   produce the Ciphertext (and base64url encoding it), and using the
   recipient's key to encrypt the CEK to produce the JWE Encrypted Key
   (and base64url encoding it).


4.  JWE Header

   The members of the JWE Header describe the encryption applied to the
   Plaintext.  Implementations MUST understand the entire contents of
   the header; otherwise, the JWE MUST be rejected for processing.

   The member names within the JWE Header are referred to as Header
   Parameter Names.  These names MUST be unique.  The corresponding
   values are referred to as Header Parameter Values.

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.

   TBD: Describe the relationship between the JWS and JWE header
   parameters - especially the "alg" parameter, which can contain either
   signature algorithms (from JWS) or encryption algorithms (from JWE),
   and the key reference parameters "jku", "kid", "x5u", and "x5t".















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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 reserved "alg"  |
   |           |        |             | values is presented in         |
   |           |        |             | Table 3.  The processing of    |
   |           |        |             | the "alg" (algorithm) header   |
   |           |        |             | parameter requires that the    |
   |           |        |             | value of the "alg" header      |
   |           |        |             | parameter 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         |
   |           |        |             | reserved "enc" values is       |
   |           |        |             | presented in Table 4.  The     |
   |           |        |             | processing of the "enc"        |
   |           |        |             | (encryption method) header     |
   |           |        |             | parameter requires that the    |
   |           |        |             | value of the "enc" header      |
   |           |        |             | parameter MUST be one that is  |
   |           |        |             | supported.  The "enc" value is |
   |           |        |             | case sensitive.  This header   |
   |           |        |             | parameter is REQUIRED.         |
   | iv        | string | String      | Initialization Vector ("iv")   |
   |           |        |             | value for algorithms requiring |
   |           |        |             | it, represented as a base64url |
   |           |        |             | encoded string.  This header   |
   |           |        |             | parameter is OPTIONAL.         |








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   | epk       | object | JWK Key     | Ephemeral Public Key ("epk")   |
   |           |        | Object      | 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   |
   |           |        |             | "curve", "x", and "y" members. |
   |           |        |             | The inclusion of the JWK Key   |
   |           |        |             | Object "algorithm" member is   |
   |           |        |             | OPTIONAL.  This header         |
   |           |        |             | parameter is OPTIONAL.         |
   | 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.         |




















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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 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.         |
   | 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.         |



















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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  |
   |           |        |             | 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.                      |
   | 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 10.  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].             |
   +-------------+-----------------------------------------------------+

               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 MUST take reasonable precautions to make sure
   they are in control of the part of the namespace they use to define
   the header parameter name.

   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.

   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:

   1.   Generate a random Content Encryption Key (CEK).  The CEK MUST
        have a length at least equal to that of the required encryption
        keys and MUST be generated randomly.  See RFC 4086 [RFC4086] for
        considerations on generating random values.

   2.   Encrypt the CEK for the recipient (see Section 7).




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   3.   Generate a random IV (if required for the algorithm).

   4.   Compress the Plaintext if a "zip" parameter was included.

   5.   Serialize the (compressed) Plaintext into a bitstring M.

   6.   Encrypt M using the CEK and IV to form the bitstring C.

   7.   Set the Encoded JWE Ciphertext equal to the base64url encoded
        representation of C.

   8.   Create the JWE Header containing the encryption parameters used.

   9.   Base64url encoded the UTF-8 representation of the JWE Header to
        create the Encoded JWE Header.

   10.  The three encoded parts, taken together, are the result of the
        encryption.


6.  Message Decryption

   The message decryption process is the reverse of the encryption
   process.  If any of these steps fails, the JWE MUST be rejected.

   1.  The Encoded JWE Header, the Encoded JWE Encrypted Key, and the
       Encoded JWE Ciphertext MUST be successfully base64url decoded
       following the restriction that no padding characters have been
       used.

   2.  The resulting JWE Header MUST be completely valid JSON syntax
       conforming to RFC 4627 [RFC4627].

   3.  The resulting JWE Header MUST be validated to only include
       parameters and values whose syntax and semantics are both
       understood and supported.

   4.  Verify that the JWE Header appears to reference a key known to
       the recipient.

   5.  Decrypt the JWE Encrypted Key to produce the CEK.

   6.  Decrypt the binary representation of the JWE Ciphertext using the
       CEK.

   7.  Uncompress the result of the previous step, if a "zip" parameter
       was included.




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   8.  Output the result.


7.  CEK Encryption

   JWE supports two forms of CEK encryption:

   o  Asymmetric encryption under the recipient's public key.

   o  Symmetric encryption under a shared key.

7.1.  Asymmetric Encryption

   In the asymmetric encryption mode, the CEK is encrypted under the
   recipient's public key.  The asymmetric encryption modes defined for
   use with this in this specification are listed in in Table 3.

7.2.  Symmetric Encryption

   In the symmetric encryption mode, the CEK 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 in Table 3.  For GCM, the random 64-bit IV is prepended to
   the ciphertext.


8.  Composition

   This document does not specify a combination signed and encrypted
   mode.  However, because the contents of a message can be arbitrary,
   encryption and data origin authentication can be provided by
   recursively encapsulating multiple JWE and JWS messages.  In general,
   senders SHOULD sign the message and then encrypt the result (thus
   encrypting the signature).  This prevents attacks in which the
   signature is stripped, leaving just an encrypted message, as well as
   providing privacy for the signer.


9.  Encrypting JWEs with Cryptographic Algorithms

   JWE uses cryptographic algorithms to encrypt the Content Encryption
   Key (CEK) and the Plaintext.  This section specifies a set of
   specific algorithms for these purposes.

   The table below Table 3 is the set of "alg" header parameter values
   that are reserved by this specification.  These algorithms are used
   to encrypt the CEK, which produces the JWE Encrypted Key.




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   +-----------+-------------------------------------------------------+
   | alg       | Encryption Algorithm                                  |
   | Parameter |                                                       |
   | Value     |                                                       |
   +-----------+-------------------------------------------------------+
   | RSA1_5    | RSA using RSA-PKCS1-1.5 padding, as defined in RFC    |
   |           | 3447 [RFC3447]                                        |
   | RSA-OAEP  | RSA using Optimal Asymmetric Encryption Padding       |
   |           | (OAEP), as defined in RFC 3447 [RFC3447]              |
   | ECDH-ES   | Elliptic Curve Diffie-Hellman Ephemeral Static, as    |
   |           | defined in RFC 6090 [RFC6090], and using the Concat   |
   |           | KDF, as defined in [NIST-800-56A], where the Digest   |
   |           | Method is SHA-256                                     |
   | A128KW    | Advanced Encryption Standard (AES) Key Wrap Algorithm |
   |           | using 128 bit keys, as defined in RFC 3394 [RFC3394]  |
   | A256KW    | Advanced Encryption Standard (AES) Key Wrap Algorithm |
   |           | using 256 bit keys, as defined in RFC 3394 [RFC3394]  |
   | A128GCM   | Advanced Encryption Standard (AES) using 128 bit keys |
   |           | in Galois/Counter Mode, as defined in [FIPS-197] and  |
   |           | [NIST-800-38D]                                        |
   | A256GCM   | Advanced Encryption Standard (AES) using 256 bit keys |
   |           | in Galois/Counter Mode, as defined in [FIPS-197] and  |
   |           | [NIST-800-38D]                                        |
   +-----------+-------------------------------------------------------+

                Table 3: JWE Reserved alg Parameter Values

   The table below Table 4 is the set of "enc" header parameter values
   that are reserved by this specification.  These algorithms are used
   to encrypt the Plaintext, which produces the Ciphertext.

   +-----------+-------------------------------------------------------+
   | enc       | Symmetric Encryption Algorithm                        |
   | Parameter |                                                       |
   | Value     |                                                       |
   +-----------+-------------------------------------------------------+
   | A128CBC   | Advanced Encryption Standard (AES) using 128 bit keys |
   |           | in Cipher Block Chaining mode, as defined in          |
   |           | [FIPS-197] and [NIST-800-38A]                         |
   | A256CBC   | Advanced Encryption Standard (AES) using 256 bit keys |
   |           | in Cipher Block Chaining mode, as defined in          |
   |           | [FIPS-197] and [NIST-800-38A]                         |
   | A128GCM   | Advanced Encryption Standard (AES) using 128 bit keys |
   |           | in Galois/Counter Mode, as defined in [FIPS-197] and  |
   |           | [NIST-800-38D]                                        |






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   | A256GCM   | Advanced Encryption Standard (AES) using 256 bit keys |
   |           | in Galois/Counter Mode, as defined in [FIPS-197] and  |
   |           | [NIST-800-38D]                                        |
   +-----------+-------------------------------------------------------+

                Table 4: JWE Reserved enc Parameter Values

   Of these algorithms, only RSA-PKCS1-1.5 with 2048 bit keys, AES-128-
   CBC, and AES-256-CBC MUST be implemented by conforming
   implementations.  It is RECOMMENDED that implementations also support
   ECDH-ES with 256 bit keys, AES-128-GCM, and AES-256-GCM.  Support for
   other algorithms and key sizes is OPTIONAL.

9.1.  Encrypting a JWE with TBD

   TBD: Descriptions of the particulars of each specified algorithm go
   here.

9.2.  Additional Algorithms

   Additional algorithms MAY be used to protect JWEs with corresponding
   "alg" and "enc" header parameter values being defined to refer to
   them.  New "alg" and "enc" header parameter values SHOULD either be
   defined in the IANA JSON Web Encryption Algorithms registry or be a
   URI that contains a collision resistant namespace.  In particular,
   the use of algorithm identifiers defined in
   [W3C.REC-xmlenc-core-20021210], [W3C.CR-xmlenc-core1-20110303], and
   related specifications is permitted.


10.  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.

   o  A new IANA registry entitled "JSON Web Encryption Algorithms" for
      reserved values used with the "alg" and "enc" header parameter
      values, as defined in Section 9.2.  Inclusion in the registry is
      RFC Required in the RFC 5226 [RFC5226] sense.  The registry will
      record the "alg" or "enc" value and a pointer to the RFC that



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      defines it.  This specification defines inclusion of the algorithm
      values defined in Table 3 and Table 4.


11.  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.

11.1.  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
   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



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   exercising limitations present in the underlying JSON implementation,
   then input containing them MUST be rejected.


12.  Open Issues and Things To Be Done (TBD)

   The following items remain to be done in this draft:

   o  Describe the relationship between the JWE, JWS, and JWT header
      parameters.  In particular, point out that the set of "alg" values
      defined by each must be compatible and non-overlapping.

   o  Consider whether we want to define composite signing/encryption
      operations (as was the consensus to do at IIW, as documented at
      http://self-issued.info/?p=378).

   o  Consider whether reusing the JWS "jku", "kid", "x5u", and "x5t"
      parameters is the right thing to do, particularly as it
      effectively precludes specifying composite operations.

   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  Consider which of the open issues from the JWS and JWT specs also
      apply here.

   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.

   o  Finish the Security Considerations section.

   o  Write a note in the Security Considerations section about how
      "x5t" (x.509 certificate thumbprint) should be deprecated because
      of known problems with SHA-1.

   o  Should StringOrURI use IRIs rather than RFC 3986 URIs?

   o  Provide a more robust description of the use of the IV.  The
      current statement "For GCM, the random 64-bit IV is prepended to



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      the ciphertext" in the Symmetric Encryption section is almost
      certainly out of place.

   o  It would be good to say somewhere, in normative language, that
      eventually the algorithms and/or key sizes currently specified
      will no longer be considered sufficiently secure and will be
      removed.  Therefore, implementers MUST be prepared for this
      eventuality.

   o  Consider whether a media type should be proposed, such as
      "application/jwe".

   o  Should we define the use of RFC 5649 key wrapping functions, which
      allow arbitrary key sizes, in addition to the current use of RFC
      3394 key wrapping functions, which require that keys be multiples
      of 64 bits?  Is this needed in practice?


13.  References

13.1.  Normative References

   [FIPS-197]
              National Institute of Standards and Technology (NIST),
              "Advanced Encryption Standard (AES)", FIPS PUB 197,
              November 2001.

   [JWK]      Jones, M., "JSON Web Key (JWK)", October 2011.

   [JWS]      Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer,
              J., Sakimura, N., and P. Tarjan, "JSON Web Signature
              (JWS)", October 2011.

   [NIST-800-38A]
              National Institute of Standards and Technology (NIST),
              "Recommendation for Block Cipher Modes of Operation",
              NIST PUB 800-38A, December 2001.

   [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



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              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.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, September 2002.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003.

   [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.

   [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.




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   [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.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              April 2010.

   [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.

13.2.  Informative References

   [I-D.rescorla-jsms]
              Rescorla, E. and J. Hildebrand, "JavaScript Message
              Security Format", draft-rescorla-jsms-00 (work in
              progress), March 2011.

   [JCA]      Oracle, "Java Cryptography Architecture", 2011.

   [JSS]      Bradley, J. and N. Sakimura (editor), "JSON Simple Sign",
              September 2010.

   [JWT]      Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer,
              J., Sakimura, N., and P. Tarjan, "JSON Web Token (JWT)",
              October 2011.

   [RFC3275]  Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup
              Language) XML-Signature Syntax and Processing", RFC 3275,
              March 2002.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [W3C.CR-xmlenc-core1-20110303]
              Hirsch, F., Reagle, J., Eastlake, D., and T. Roessler,
              "XML Encryption Syntax and Processing Version 1.1", World
              Wide Web Consortium CR CR-xmlenc-core1-20110303,
              March 2011,
              <http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303>.




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   [W3C.REC-xmlenc-core-20021210]
              Eastlake, D. and J. Reagle, "XML Encryption Syntax and
              Processing", World Wide Web Consortium Recommendation REC-
              xmlenc-core-20021210, December 2002,
              <http://www.w3.org/TR/2002/REC-xmlenc-core-20021210>.


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.  Algorithm Identifier Cross-Reference

   This appendix contains a table cross-referencing the "alg" and "enc"
   values used in this specification with the equivalent identifiers
   used by other standards and software packages.  See XML DSIG
   [RFC3275] and Java Cryptography Architecture [JCA] for more
   information about the names defined by those documents.

   +---------+------+-------------------------+-------------------+----+
   | Algorit | JWE  | XML ENC                 | JCA               | OI |
   | hm      |      |                         |                   | D  |
   +---------+------+-------------------------+-------------------+----+
   | RSA     | RSA1 | http://www.w3.org/2001/ | RSA/ECB/PKCS1Padd | TB |
   | using   | _5   | 04/xmlenc#rsa-1_5       | ing               | D  |
   | RSA-PKC |      |                         |                   |    |
   | S1-1.5  |      |                         |                   |    |
   |  paddin |      |                         |                   |    |
   | g       |      |                         |                   |    |











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   | RSA     | RSA- | http://www.w3.org/2001/ | RSA/ECB/OAEPWithS | TB |
   | using   | OAEP | 04/xmlenc#rsa-oaep-mgf1 | HA-1AndMGF1Paddin | D  |
   | Optimal |      | p                       | g                 |    |
   | Asymmet |      |                         |                   |    |
   | ric     |      |                         |                   |    |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Paddi |      |                         |                   |    |
   | ng(OAEP |      |                         |                   |    |
   | )       |      |                         |                   |    |
   | Ellipti | ECDH | http://www.w3.org/2009/ | TBD               | TB |
   | cCurve  | -ES  | xmlenc11#ECDH-ES        |                   | D  |
   |  Diffie |      |                         |                   |    |
   | -Hellma |      |                         |                   |    |
   | n Ephem |      |                         |                   |    |
   | eral    |      |                         |                   |    |
   |    Stat |      |                         |                   |    |
   | ic      |      |                         |                   |    |
   | Advance | A128 | http://www.w3.org/2001/ | TBD               | TB |
   | d       | KW   | 04/xmlenc#kw-aes128     |                   | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  Key  |      |                         |                   |    |
   |    Wrap |      |                         |                   |    |
   |    Algo |      |                         |                   |    |
   | rithm R |      |                         |                   |    |
   | FC  339 |      |                         |                   |    |
   | 4   [RF |      |                         |                   |    |
   | C3394]  |      |                         |                   |    |
   | using12 |      |                         |                   |    |
   | 8 bitke |      |                         |                   |    |
   | ys      |      |                         |                   |    |

















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   | Advance | A256 | http://www.w3.org/2001/ | TBD               | TB |
   | d       | KW   | 04/xmlenc#kw-aes256     |                   | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  Key  |      |                         |                   |    |
   |    Wrap |      |                         |                   |    |
   |    Algo |      |                         |                   |    |
   | rithm R |      |                         |                   |    |
   | FC  339 |      |                         |                   |    |
   | 4   [RF |      |                         |                   |    |
   | C3394]  |      |                         |                   |    |
   | using25 |      |                         |                   |    |
   | 6 bitke |      |                         |                   |    |
   | ys      |      |                         |                   |    |
   | Advance | A128 | http://www.w3.org/2001/ | AES/CBC/PKCS5Padd | TB |
   | d       | CBC  | 04/xmlenc#aes128-cbc    | ing               | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  usin |      |                         |                   |    |
   | g  128  |      |                         |                   |    |
   | bitkeys |      |                         |                   |    |
   |  inCiph |      |                         |                   |    |
   | er Bloc |      |                         |                   |    |
   | k  Chai |      |                         |                   |    |
   | ningmod |      |                         |                   |    |
   | e       |      |                         |                   |    |
   | Advance | A256 | http://www.w3.org/2001/ | AES/CBC/PKCS5Padd | TB |
   | d       | CBC  | 04/xmlenc#aes256-cbc    | ing               | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  usin |      |                         |                   |    |
   | g  256  |      |                         |                   |    |
   | bitkeys |      |                         |                   |    |
   |  inCiph |      |                         |                   |    |
   | er Bloc |      |                         |                   |    |
   | k  Chai |      |                         |                   |    |
   | ningmod |      |                         |                   |    |
   | e       |      |                         |                   |    |







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   | Advance | A128 | http://www.w3.org/2009/ | AES/GCM/NoPadding | TB |
   | d       | GCM  | xmlenc11#aes128-gcm     |                   | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  usin |      |                         |                   |    |
   | g  128  |      |                         |                   |    |
   | bitkeys |      |                         |                   |    |
   |  inGalo |      |                         |                   |    |
   | is/Coun |      |                         |                   |    |
   | ter Mod |      |                         |                   |    |
   | e       |      |                         |                   |    |
   | Advance | A256 | http://www.w3.org/2009/ | AES/GCM/NoPadding | TB |
   | d       | GCM  | xmlenc11#aes256-gcm     |                   | D  |
   |  Encryp |      |                         |                   |    |
   | tion    |      |                         |                   |    |
   |   Stand |      |                         |                   |    |
   | ard(AES |      |                         |                   |    |
   | )  usin |      |                         |                   |    |
   | g  256  |      |                         |                   |    |
   | bitkeys |      |                         |                   |    |
   |  inGalo |      |                         |                   |    |
   | is/Coun |      |                         |                   |    |
   | ter Mod |      |                         |                   |    |
   | e       |      |                         |                   |    |
   +---------+------+-------------------------+-------------------+----+

               Table 5: Algorithm Identifier Cross-Reference


Appendix C.  Acknowledgements

   Solutions for encrypting JSON content were also explored by [JSS] and
   [I-D.rescorla-jsms], both of which significantly influenced this
   draft.  This draft attempts to explicitly reuse as much from
   [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 some of
   the text from [I-D.rescorla-jsms] in this document.


Appendix D.  Document History

   -01



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   o  Changed type of Ephemeral Public Key ("epk") from string to JSON
      object, so that a JWK Key Object value can be used directly.

   o  Specified that the Digest Method for ECDH-ES is SHA-256.  (The
      specification was previously silent about the choice of digest
      method.)

   o  The "jku" and "x5u" URLs are now required to be absolute URLs.

   o  Removed this unnecessary language from the "kid" description:
      "Omitting this parameter is equivalent to setting it to an empty
      string".

   o  Use the same language as RFC 2616 does when describing "GZIP"
      message compression.

   -00

   o  First encryption draft based upon consensus decisions at IIW
      documented at http://self-issued.info/?p=378.  The ability to
      provide encryption for JSON Web Tokens (JWTs) [JWT] is a primary
      use case.


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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