wdiff rfc5708.original rfc5708.txt

Internet-Draft A.D.
Independent Submission A. Keromytis
Expires: October 20, 2009
Request for Comments: 5708 Columbia University
Intended Status: Proposed March 25, 2009
Filename: draft-keromytis-keynote-x509-02.txt
Category: Informational January 2010
ISSN: 2070-1721

X.509 Key and Signature Encoding for the
KeyNote Trust Management System

Status of this Memo

Abstract

This Internet-Draft is submitted to memo describes X.509 key identifiers and signature encoding for
version 2 of the IETF KeyNote trust-management system (RFC 2704). X.509
certificates (RFC 5280) can be directly used in the Authorizer or
Licensees field (or in both fields) in full conformance a KeyNote assertion, allowing
for easy integration with protocols that already use X.509
certificates for authentication.

In addition, the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of document defines additional signature types that use
other hash functions (beyond the Internet Engineering
Task Force (IETF), its areas, MD5 and its working groups. Note SHA1 hash functions that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid
defined in RFC 2792).

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This is a maximum contribution to the RFC Series, independently of six
months any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and may be updated, replaced, makes no statement about its value for
implementation or obsoleted deployment. Documents approved for publication by other
documents at
the RFC Editor are not a candidate for any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."

The list level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list status of Internet-Draft Shadow Directories can this document, any errata,
and how to provide feedback on it may be accessed obtained at
http://www.ietf.org/shadow.html.
http://www.rfc-editor.org/info/rfc5708.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http:trustee.ietf.org/license-info) in effect on the date of
publication of this document (http://trustee.ietf.org/licenseinfo). document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.

Abstract

This memo describes X.509 key identifiers and signature encoding
for version 2 of the KeyNote trust-management system [KEYNOTE].
X.509 certificates [RFC3280] can be directly used in the Authorizer
or Licensees field (or in both fields) in a KeyNote assertion,
allowing for easy integration with protocols that already use X.509
certificates for authentication.

In addition, the document defines additional signature types that
use other hash functions (beyond the MD5 and SHA1 hash functions
that are defined in [RFC2792]).

1. Introduction

KeyNote is a simple and flexible trust-management system designed to
work well for a variety of large- and small-scale small-scale, Internet-based
applications. It provides a single, unified language for both local
policies and credentials. KeyNote policies and credentials, called
`assertions',
'assertions', contain predicates that describe the trusted actions
permitted by the holders of specific public keys. KeyNote assertions
are essentially small, highly-structured highly structured programs. A signed
assertion, which can be sent over an untrusted network, is also
called a `credential 'credential assertion'. Credential assertions, which also
serve the role of certificates, have the same syntax as policy
assertions but are also signed by the principal delegating the trust.
Note that only one principal may sign a credential assertion, but
trust may be delegated to multiple principals. The credential
assertion may delegate trust to each of these principals separately, separately
or to groups of principals required to act together. For more
details on KeyNote, see [KEYNOTE]. This document assumes reader
familiarity with the KeyNote system.

Cryptographic keys may be used in KeyNote to identify principals. To
facilitate interoperation between different implementations and to
allow for maximal flexibility, keys must be converted to a normalized
canonical form (depended (dependent on the public key algorithm used) for the
purposes of any internal comparisons between keys. For example, an
RSA key may be encoded in base64 [RFC4648] ASCII in one credential, credential
and in hexadecimal ASCII in another. A KeyNote implementation must
internally convert the two encodings to a normalized form that allows
for comparison between them. Furthermore, the internal structure of
an encoded key must be known for an implementation to correctly
decode it. RFC 2792 [RFC2792] describes the RSA and DSA (Digital Signature
Algorithm) key identifier and signature encodings for use in KeyNote
assertions. This document specifies a new key identifier, allowing
X.509 certificates [RFC3280] [RFC5280] to be used as a key substitute wherever
an RSA or DSA key may be used in KeyNote. Specifically, KeyNote will
use the key associated with the Subject subject of an X.509 certificate. In
addition, this document defines a corresponding signature encoding,
to be used in conjunction with X.509 key identifiers. Finally, this
document defines new signature encodings that use new hash functions
beyond the MD5 and SHA1 functions defined in RFC 2792, and which in
recent years have been found to be vulnerable to attack.

1.1. Conventions

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].

2. X.509 Key Identifier Encoding

X.509 key identifiers in KeyNote are encoded as an ASN1 DER Distinguished
Encoding Rules (DER) encoding of the whole X.509 certificate, as
defined in Section 4 of RFC 3280
[RFC3280]. [RFC5280].

For use in KeyNote credentials, the ASN1 DER-encoded object is then
ASCII- encoded
ASCII-encoded (e.g., as a string of hex digits or base64 characters).

X.509 keys encoded in this way in KeyNote must be identified by the
"x509-XXX:" algorithm name, where XXX is an ASCII encoding ("hex" or
"base64"). Other ASCII encoding schemes may be defined in the
future.

3. X.509 Key Identifier Normalized Forms

For comparison purposes, X.509 certificates are parsed, the Subject public key in X.509 certificates
is extracted and decomposed according to used in the rules normalized form described in Section 2 of [RFC2792].
The resulting RSA or DSA key is then used for comparing, per
[RFC2792]. All X.509 key comparisons in KeyNote occur between
normalized forms. Note that this allows for comparison between a
directly encoded RSA or DSA key (as specified in RFC 2792) and the
same key when contained in an X.509 certificate.

4. X.509 Signature Computation and Encoding

X.509 key identifier signatures are defined for historical reasons.
Implementers are encouraged to use the RSA RSA- or DSA-based signature
encodings instead.

X.509 key identifier signatures in KeyNote are identical to RSA- or
DSA-based signatures [RFC2792]. The only difference is that the
public key corresponding to the private key that generated the
signatures is encoded in an X.509 certificate in the ``Authorizer'' Authorizer field
of the signed credential assertion. However, an RSA- or DSA-based
signature encoding (depending on the Subject key contained in the
X.509 certificate itself) may be used instead.

X.509 key identifier signatures in KeyNote are computed over the
assertion body (starting from the beginning of the first keyword, up
to and including the newline character immediately before the
"Signature:" keyword) and the signature algorithm name (including the
trailing colon character, e.g., "sig-x509-sha512-base64:")

X.509 key identifier signatures are encoded as an ASN1 OCTET STRING
object, containing the signature value.

For use in KeyNote credentials, the ASN1 OCTET STRING is then ASCII-
encoded (as a string of hex digits or base64 characters).

X.509 key identifier signatures encoded in this way in KeyNote must
be identified by the "sig-x509-XXX-YYY:" algorithm name, where XXX is
a hash function name (see Section 5 and Section 7 of this document)
and YYY is an ASCII encoding ("hex" or "base64").

5. Hash Functions For RSA, DSA, and X.509 Key Identifier Signatures

For historical reasons (backward compatibility), X.509 key identifier
signatures SHOULD support SHA1 as the hash function, using the "sha1"
keyword. In addition, SHA256, SHA512 SHA512, and RIPEMD160 [SHA256+] [SHA2-2] [RIPEMD-160] ([SHA256+],
[SHA2-2], [RIPEMD-160]) signatures MUST be supported for use with X509
X.509 key identifier signatures, by using the "sha256", "sha512" "sha512", and
"ripemd160" keywords keywords, respectively (see Section 7).

In addition, SHA256, SHA512 SHA512, and RIPEMD160 signature identifiers are
defined for RSA signatures, using the "sha256", "sha512" "sha512", and
"ripemd160" keywords keywords, respectively (see Section 7).

6. Security Considerations

This document discusses the format of X.509 keys and signatures as
used in KeyNote. The security of KeyNote credentials utilizing such
keys and credentials is directly dependent on the strength of the
related public key algorithms. On the security of KeyNote itself,
see [KEYNOTE]. Furthermore, it is the responsibility of the
application developer to ensure that X.509 certificates are valid
(signed by a trusted authority, not expired, and not revoked).

The use of SHA1 as part of signatures and key identifiers is
discouraged, because of the various weaknesses in the algorithm that
have been identified in recent years.

7. IANA Considerations

Per [KEYNOTE], [RFC2792], IANA should provide has provided a registry of reserved algorithm
identifiers. The following identifiers are reserved by this document as KeyNote
public key identifier encodings: format identifiers:

- "x509-hex"
- "x509-base64"

The following identifiers are reserved by this document as KeyNote signature
encodings:
algorithm identifiers:

- "sig-x509-sha1-hex"
- "sig-x509-sha1-base64"
- "sig-x509-sha256-hex"
- "sig-x509-sha256-base64"
- "sig-x509-sha512-hex"
- "sig-x509-sha512-base64"
- "sig-x509-ripemd160-hex"
- "sig-x509-ripemd160-base64"
- "sig-rsa-sha256-hex"
- "sig-rsa-sha256-base64"
- "sig-rsa-sha512-hex"
- "sig-rsa-sha512-base64"
- "sig-rsa-ripemd160-hex"
- "sig-rsa-ripemd160-base64"

Note that the double quotes are not part of the algorithm
identifiers.

8. References

8.1. Normative References

[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.

[SHA256+] Eastlake, Eastlake 3rd, D. and T. Hansen, "US Secure Hash
Algorithms (SHA and HMAC-SHA)", RFC 4634, July 2006.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[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.

8.2. Informative References

[KEYNOTE] Blaze, M., Feigenbaum, J., Ioannidis, J., and A.
Keromytis, "The KeyNote Trust-Management System, System Version
2", RFC 2704, September 1999.

[RIPEMD-160] 3.ISO/IEC 10118-3:1998, "Information technology -
Security techniques - Hash-functions - Part 3:
Dedicated hash-functions," International Organization
for Standardization, Geneva, Switzerland, 1998.

[RFC2792] Blaze, M., Ioannidis, J., and A. Keromytis, "DSA and RSA
Key and Signature Encoding for the KeyNote Trust
Management System", RFC 2792, March 2000.

[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.

[RIPEMD-160] 3.ISO/IEC 10118-3:1998, "Information technology -
Security techniques - Hash-functions - Part 3: Dedicated
hash-functions," International Organization for
Standardization, Geneva, Switzerland, 1998.

[SHA2-2] NIST, "Descriptions of SHA-256, SHA-384, and SHA-512",
May 2001,
<http://csrc.nist.gov/cryptval/shs/sha256-384-512.pdf>.

10. <http://csrc.nist.gov/publications/fips/
fips180-3/fips180-3_final.pdf>.

9. Acknowledgements

The author would like to thank Jim Schaad for his review and comments
on earlier versions of this document.

Authors' Addresses

Author's Address

Angelos D. Keromytis
Department of Computer Science
Columbia University
Mail Code 0401
1214 Amsterdam Avenue
New York, New York 1007
USA
angelos <at> cs <dot> columbia <dot> edu

EMail: angelos@cs.columbia.edu