Network Working Group                                           M. Blaze
Request for Comments: 2792                                  J. Ioannidis
Category: Informational                             AT&T Labs - Research
                                                           A. Keromytis
                                                     U. of Pennsylvania
                                                             March 2000


            DSA and RSA Key and Signature Encoding for the
                   KeyNote Trust Management System

Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

  This memo describes RSA and DSA key and signature encoding, and
  binary key encoding for version 2 of the KeyNote trust-management
  system.

1.  Introduction

  KeyNote is a simple and flexible trust-management system designed to
  work well for a variety of large- and small-scale Internet-based
  applications.  It provides a single, unified language for both local
  policies and credentials.  KeyNote policies and credentials, called
  `assertions', contain predicates that describe the trusted actions
  permitted by the holders of specific public keys.  KeyNote assertions
  are essentially small, highly-structured programs.  A signed
  assertion, which can be sent over an untrusted network, is also
  called a `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.
  For more details on KeyNote, see [BFIK99].  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 on the public key algorithm used) for the
  purposes of any internal comparisons between keys.  For example, an



Blaze, et al.                Informational                      [Page 1]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


  RSA [RSA78] key may be encoded in base64 ASCII in one 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.

  In some applications, other types of values, such as a passphrase or
  a random nonce, may be used as principal identifiers.  When these
  identifiers contain characters that may not appear in a string (as
  defined in [BFIK99]), a simple ASCII encoding is necessary to allow
  their use inside KeyNote assertions.  Note that if the identifier
  only contains characters that can appear in a string, it may be used
  as-is.  Naturally, such identifiers may not be used to sign an
  assertion, and thus no related signature encoding is defined.

  This document specifies RSA and DSA [DSA94] key and signature
  encodings, and binary key encodings for use in KeyNote.

2.  Key Normalized Forms

2.1  DSA Key Normalized Form

  DSA keys in KeyNote are identified by four values:

  - the public value, y
  - the p parameter
  - the q parameter
  - the g parameter

  Where the y, p, q, and g are the DSA parameters corresponding to the
  notation of [Sch96]. These four values together make up the DSA key
  normalized form used in KeyNote.  All DSA key comparisons in KeyNote
  occur between normalized forms.

2.2  RSA Key Normalized Form

  RSA keys in KeyNote are identified by two values:

  - the public exponent
  - the modulus

  These two values together make up the RSA key normalized form used in
  KeyNote.  All RSA key comparisons in KeyNote occur between normalized
  forms.






Blaze, et al.                Informational                      [Page 2]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


2.3  Binary Identifier Normalized Form

  The normalized form of a Binary Identifier is the binary identifier's
  data.  Thus, Binary Identifier comparisons are essentially binary-
  string comparisons of the Identifier values.

3.  Key Encoding

3.1  DSA Key Encoding

  DSA keys in KeyNote are encoded as an ASN1 SEQUENCE of four ASN1
  INTEGER objects.  The four INTEGER objects are the public value and
  the p, q, and g parameters of the DSA key, in that order.

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

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

3.2  RSA Key Encoding

  RSA keys in KeyNote are encoded as an ASN1 SEQUENCE of two ASN1
  INTEGER objects.  The two INTEGER objects are the public exponent and
  the modulus of the DSA key, in that order.

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

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

3.3  Binary Identifier Encoding

  Binary Identifiers in KeyNote are assumed to have no internal
  encoding, and are treated as a sequence of binary digits.  The Binary
  Identifiers are ASCII-encoded, similarly to RSA or DSA keys.

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





Blaze, et al.                Informational                      [Page 3]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


4.  Signature Computation and Encoding

4.1  DSA Signature Computation and Encoding

  DSA 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-dsa-sha1-base64:")

  DSA signatures are then encoded as an ASN1 SEQUENCE of two ASN1
  INTEGER objects.  The two INTEGER objects are the r and s values of a
  DSA signature [Sch96], in that order.

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

  DSA signatures encoded in this way in KeyNote must be identified by
  the "sig-dsa-XXX-YYY:" algorithm name, where XXX is a hash function
  name ("sha1", for the SHA1 [SHA1-95] hash function is currently the
  only hash function that may be used with DSA) and YYY is an ASCII
  encoding ("hex" or "base64").

4.2  RSA Signature Computation and Encoding

  RSA 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-rsa-sha1-base64:")

  RSA signatures are then 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).

  RSA signatures encoded in this way in KeyNote must be identified by
  the "sig-rsa-XXX-YYY:" algorithm name, where XXX is a hash function
  name ("md5" or "sha1", for the MD5 [Riv92] and SHA1 [SHA1-95] hash
  algorithms respectively, may be used with RSA) and YYY is an ASCII
  encoding ("hex" or "base64").

4.3  Binary Signature Computation and Encoding

  Binary Identifiers are unstructured sequences of binary digits, and
  are not associated with any cryptographic algorithm.  Thus, they may
  not be used to validate an assertion.



Blaze, et al.                Informational                      [Page 4]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


5.  Security Considerations

  This document discusses the format of RSA and DSA keys and signatures
  and of Binary principal identifiers 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 [BFIK99].

6.  IANA Considerations

  Per [BFIK99], IANA should provide a registry of reserved algorithm
  identifiers.  The following identifiers are reserved by this document
  as public key and binary identifier encodings:

  - "rsa-hex"
  - "rsa-base64"
  - "dsa-hex"
  - "dsa-base64"
  - "binary-hex"
  - "binary-base64"

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

  - "sig-rsa-md5-hex"
  - "sig-rsa-md5-base64"
  - "sig-rsa-sha1-hex"
  - "sig-rsa-sha1-base64"
  - "sig-dsa-sha1-hex"
  - "sig-dsa-sha1-base64"

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

7.  Acknowledgments

  This work was sponsored by the DARPA Information Assurance and
  Survivability (IA&S) program, under BAA 98-34.

References

  [Sch96]   Bruce Schneier, Applied Cryptography 2nd Edition, John
            Wiley & Sons, New York, NY, 1996.

  [BFIK99]  Blaze, M., Feigenbaum, J., Ioannidis, J. and A. Keromytis,
            "The KeyNote Trust-Management System Version 2", RFC 2704,
            September 1999.




Blaze, et al.                Informational                      [Page 5]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


  [DSA94]   NIST, FIPS PUB 186, "Digital Signature Standard", May 1994.

  [Riv92]   Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
            April 1992.

  [RSA78]   R. L. Rivest, A. Shamir, L. M. Adleman, "A Method for
            Obtaining Digital Signatures and Public-Key Cryptosystems",
            Communications of the ACM, v21n2. pp 120-126, February
            1978.

  [SHA1-95] NIST, FIPS PUB 180-1, "Secure Hash Standard", April 1995.
            http://csrc.nist.gov/fips/fip180-1.txt (ascii)
            http://csrc.nist.gov/fips/fip180-1.ps  (postscript)

Contacts

  Comments about this document should be discussed on the
  [email protected] mailing list.

  Questions about this document can also be directed to the authors as
  a group at the [email protected] alias, or to the individual
  authors at:

  Matt Blaze
  AT&T Labs - Research
  180 Park Avenue
  Florham Park, New Jersey 07932-0000

  EMail: [email protected]


  John Ioannidis
  AT&T Labs - Research
  180 Park Avenue
  Florham Park, New Jersey 07932-0000

  EMail: [email protected]


  Angelos D. Keromytis
  Distributed Systems Lab
  CIS Department, University of Pennsylvania
  200 S. 33rd Street
  Philadelphia, Pennsylvania  19104-6389

  EMail: [email protected]





Blaze, et al.                Informational                      [Page 6]

RFC 2792         Key and Signature Encoding for KeyNote       March 2000


Full Copyright Statement

  Copyright (C) The Internet Society (2000).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















Blaze, et al.                Informational                      [Page 7]


You are viewing proxied material from gopher.rbfh.de. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.