Network Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track E. Rescorla
Expires: June 15, 2012 RTFM, Inc.
J. Hildebrand
Cisco Systems, Inc.
December 13, 2011
JSON Web Encryption (JWE)
draft-jones-json-web-encryption-02
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 June 15, 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
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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 . . . . . . . . . . . . . . . . . . . . 19
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 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.
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.
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 (with line breaks for
display purposes only):
eyJhbGciOiJSU0ExXzUiLA0KICJlbmMiOiJBMjU2R0NNIiwNCiAiaXYiOiJfXzc5
X1B2Ni1mZyIsDQogIng1dCI6Ijdub09QcS1oSjFfaENudldoNkllWUkydzlRMCJ9
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 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 for processing.
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 defined "alg" |
| | | | values is presented in |
| | | | Table 3. 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 |
| | | | Table 4. 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. |
| 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 |
| | | | "crv" (curve), "x", and "y" |
| | | | members. The inclusion of the |
| | | | JWK Key Object "alg" |
| | | | (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 needs to take reasonable precautions to make
sure they are in control of the part of the namespace they use to
define the header parameter name.
New header parameters should be introduced sparingly, as they can
result in non-interoperable JWEs.
4.3. Private Header Parameter Names
A producer and consumer of a JWE may agree to any header parameter
name that is not a Reserved Name Section 4.1 or a Public Name
Section 4.2. Unlike Public Names, these private names are subject to
collision and should be used with caution.
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 a JWE Header containing the encryption parameters used.
Note that white space is explicitly allowed in the
representation and no canonicalization is performed before
encoding.
9. Base64url encode the bytes of 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.
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7. Uncompress the result of the previous step, if a "zip" parameter
was included.
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
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that are defined by this specification. These algorithms are used to
encrypt the CEK, which produces the JWE Encrypted Key.
+-----------+-------------------------------------------------------+
| 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 Defined "alg" Parameter Values
The table below Table 4 is the set of "enc" header parameter values
that are defined 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 Defined "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 using 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, it
is permissible to use the algorithm identifiers defined in XML
Encryption [W3C.REC-xmlenc-core-20021210], XML Encryption 1.1
[W3C.CR-xmlenc-core1-20110303], and related specifications as "alg"
and "enc" values.
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
values used with the "alg" and "enc" header parameters is 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
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"enc" value and a pointer to the RFC that 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;
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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.
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). This would provide both
confidentiality and integrity.
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?
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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
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 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)", December 2011.
[JWS] Jones, M., Balfanz, D., Bradley, J., Goland, Y., Panzer,
J., Sakimura, N., and P. Tarjan, "JSON Web Signature
(JWS)", December 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
800-56A, March 2007.
Jones, et al. Expires June 15, 2012 [Page 17]
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[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.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Jones, et al. Expires June 15, 2012 [Page 18]
Internet-Draft JWE December 2011
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.
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)",
December 2011.
[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
Wide Web Consortium CR CR-xmlenc-core1-20110303,
March 2011,
<http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303>.
[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.
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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 Encryption
[W3C.REC-xmlenc-core-20021210], XML Encryption 1.1
[W3C.CR-xmlenc-core1-20110303], and Java Cryptography Architecture
[JCA] for more information about the names defined by those
documents.
+---------+-------+---------------------------+---------------------+
| Algorit | JWE | XML ENC | JCA |
| hm | | | |
+---------+-------+---------------------------+---------------------+
| RSA | RSA1_ | http://www.w3.org/2001/04 | RSA/ECB/PKCS1Paddin |
| using | 5 | /xmlenc#rsa-1_5 | g |
| RSA-PKC | | | |
| S1-1.5 | | | |
| paddin | | | |
| g | | | |
| RSA | RSA-O | http://www.w3.org/2001/04 | RSA/ECB/OAEPWithSHA |
| using | AEP | /xmlenc#rsa-oaep-mgf1p | -1AndMGF1Padding |
| Optimal | | | |
| Asymmet | | | |
| ric | | | |
| Encryp | | | |
| tion | | | |
| Paddi | | | |
| ng(OAEP | | | |
| ) | | | |
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| Ellipti | ECDH- | http://www.w3.org/2009/xm | TBD |
| cCurve | ES | lenc11#ECDH-ES | |
| Diffie | | | |
| -Hellma | | | |
| n Ephem | | | |
| eral | | | |
| Stat | | | |
| ic | | | |
| Advance | A128K | http://www.w3.org/2001/04 | TBD |
| d | W | /xmlenc#kw-aes128 | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) Key | | | |
| Wrap | | | |
| Algo | | | |
| rithm R | | | |
| FC 339 | | | |
| 4 [RF | | | |
| C3394] | | | |
| using12 | | | |
| 8 bitke | | | |
| ys | | | |
| Advance | A256K | http://www.w3.org/2001/04 | TBD |
| d | W | /xmlenc#kw-aes256 | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) Key | | | |
| Wrap | | | |
| Algo | | | |
| rithm R | | | |
| FC 339 | | | |
| 4 [RF | | | |
| C3394] | | | |
| using25 | | | |
| 6 bitke | | | |
| ys | | | |
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| Advance | A128C | http://www.w3.org/2001/04 | AES/CBC/PKCS5Paddin |
| d | BC | /xmlenc#aes128-cbc | g |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 128 | | | |
| bitkeys | | | |
| inCiph | | | |
| er Bloc | | | |
| k Chai | | | |
| ningmod | | | |
| e | | | |
| Advance | A256C | http://www.w3.org/2001/04 | AES/CBC/PKCS5Paddin |
| d | BC | /xmlenc#aes256-cbc | g |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 256 | | | |
| bitkeys | | | |
| inCiph | | | |
| er Bloc | | | |
| k Chai | | | |
| ningmod | | | |
| e | | | |
| Advance | A128G | http://www.w3.org/2009/xm | AES/GCM/NoPadding |
| d | CM | lenc11#aes128-gcm | |
| Encryp | | | |
| tion | | | |
| Stand | | | |
| ard(AES | | | |
| ) usin | | | |
| g 128 | | | |
| bitkeys | | | |
| inGalo | | | |
| is/Coun | | | |
| ter Mod | | | |
| e | | | |
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| Advance | A256G | http://www.w3.org/2009/xm | AES/GCM/NoPadding |
| d | CM | lenc11#aes256-gcm | |
| 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 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 some of
the text from [I-D.rescorla-jsms] in this document.
Appendix D. Document History
-02
o Update to use short JWK Key Object names in Ephemeral Public Keys.
o Moved "MUST" requirements from the Overview to later in the spec.
o Respect line length restrictions in examples.
o Applied other editorial improvements.
-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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