Network Working Group Sean Turner, IECA
Internet Draft May 7, 2010
Intended Status: Standard Track
Expires: November 7, 2010
Algorithms for Cryptographic Message Syntax (CMS)
Encrypted Key Package Content Type
draft-turner-encryptedkeypackagecontenttype-algs-02.txt
Abstract
This document describes the conventions for using several
cryptographic algorithms with the Cryptographic Message Syntax (CMS)
encrypted key package content type. Specifically, it includes
conventions necessary to implement EnvelopedData, EncryptedData, and
AuthEnvelopedData.
Status of this Memo
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Internet-Draft Algorithms for CMS Encrypted Key Packages May 2009
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1. Introduction
This document describes the conventions for using several
cryptographic algorithms with the Cryptographic Message Syntax (CMS)
encrypted key package content type [RFCTBD]. Specifically, it
includes conventions necessary to implement the following CMS content
types: EnvelopedData [RFC5652], EncryptedData [RFC5652], and
AuthEnvelopedData [RFC5083].
This document does not define any new algorithms; instead it refers
to previously defined algorithms.
1.1. Terminology
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 [RFC2119].
2. EnvelopedData
EnvelopedData [RFC5652] supports a number of key management
techniques. Implementations that claim conformance to this document
MUST support the key transport mechanisms and SHOULD support the key
agreement mechanisms as defined below. Other techniques MAY be
supported.
When key transport is used, RSA encryption [RFC3370] MUST be
supported and RSA-OAEP [RFC3560] SHOULD be supported.
When key agreement is used, Diffie-Hellman ephemeral-static [RFC3370]
MUST be supported.
Regardless of the key management technique choice, implementations
MUST support AES-128 Key Wrap with Padding [RFC5649].
Implementations SHOULD support AES-256 Key Wrap with Padding
[RFC5649].
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When key agreement is used, a key wrap algorithm is also specified to
wrap the content encryption key. If the content encryption algorithm
is AES-128 Key Wrap with Padding, then the key wrap algorithm MUST be
AES-128 Key Wrap with Padding [RFC5649]. If the content encryption
algorithm is AES-256 Key Wrap with Padding, then the key wrap
algorithm MUST be AES-256 Key Wrap with Padding [RFC5649].
3. EncryptedData
EncryptedData [RFC5652] requires that keys be managed by other means;
therefore, the only algorithm specified is the content encryption
algorithm. Implementations MUST support AES-128 Key Wrap with Padding
[RFC5649]. Implementations SHOULD support AES-256 Key Wrap with
Padding [RFC5649].
4. AuthEnvelopedData
AuthEnvelopedData [RFC5083], like EnvelopedData, supports a number of
key management techniques. The key management requirements for
AuthEnvelopedData are the same as for EnvelopedData. The difference
is the content encryption algorithm. Implementations MUST support
128-bit AES-GCM [RFC5084] and SHOULD support 256-bit AES-GCM
[RFC5084]. Implementations MAY also support AES-CCM [RFC5084].
5. Public Key Sizes
The easiest way to implement the key transport requirement for
EnvelopedData and AuthEnvelopedData is with public key certificates
[RFC5280]. If an implementation supports RSA, RSAES-OAEP, or DH,
then it MUST support key lengths from 1024-bit to 2048-bit,
inclusive.
6. Security Considerations
The security considerations from [RFC3370], [RFC3560], [RFC5083],
[RFC5084], [RFC5649], [RFC5652], and [RFCTBD] apply.
The choice of content encryption algorithms for this document was
based on [RFC5649]: "In the design of some high assurance
cryptographic modules, it is desirable to segregate cryptographic
keying material from other data. The use of a specific cryptographic
mechanism solely for the protection of cryptographic keying material
can assist in this goal." Unfortunately, there is no AES-GCM or AES-
CCM mode that provides the same properties. If an AES-GCM and AES-
CCM mode that provides the same properties is defined, then this
document will be updated to adopt that algorithm.
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[SP800-57] provides comparable bits of security for some algorithms
and key sizes. [SP800-57] also provides time frames during which
certain numbers of bits of security are appropriate and some
environments may find these time frames useful.
7. IANA Considerations
None. Please remove this section prior to publication as an RFC.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3370] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[RFC3560] Housley, R., "Use of the RSAES-OAEP Key Transport
Algorithm in the Cryptographic Message Syntax (CMS)", RFC
3560, July 2003.
[RFC5083] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083,
November 2007.
[RFC5084] Housley, R., "Using AES-CCM and AES-GCM Authenticated
Encryption in the Cryptographic Message Syntax (CMS)",
RFC 5084, November 2007.
[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.
[RFC5649] Housley, R., and M. Dworkin, "Advanced Encryption
Standard (AES) Key Wrap with Padding Algorithm", RFC
5649, September 2009.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
5652, September 2009.
[RFCTBD] Turner, S., and R. Housley, "Cryptographic Message Syntax
(CMS) Encrypted Key Package Content Type", draft-turner-
encryptedkeypackagecontenttype-02.txt, work-in-progress.
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/**
RFC Editor: Please replace "TBD" with the number of the published
RFC. Please do this in both the references and the text.
**/
8.2. Informative References
[SP800-57] National Institute of Standards and Technology (NIST),
Special Publication 800-57: Recommendation for Key
Management - Part 1 (Revised), March 2007.
Authors' Addresses
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
EMail: turners@ieca.com
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