Container Authenticated by Multiple MACs
draft-ietf-krb-wg-cammac-01

Internet Engineering Task Force                            S. Sorce, Ed.
Internet-Draft                                                   Red Hat
Intended status: Standards Track                              T. Yu, Ed.
Expires: August 12, 2012                                T. Hardjono, Ed.
                                                 MIT Kerberos Consortium
                                                             Feb 9, 2012

                Container Authenticated by Multiple MACs
                      draft-ietf-krb-wg-cammac-01

Abstract

   Abstract: This document proposes a Kerberos Authorization Data
   container similar to AD-KDC-ISSUED, but that allows for multiple MACs
   or signatures on the contained Authorization Data elements.

Status of this Memo

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   This Internet-Draft will expire on August 12, 2012.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   3.  Validation  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  AD-CAMMAC . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Assigned numbers  . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Additional Stuff . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   This draft proposes a Authorization Data container for Kerberos that
   identifies a base set of MAC and other elements necessary to
   authenticate the authorization data being carried in such a way that
   not only the KDC but also services can independently verify that the
   data has been authenticated by the KDC and has not been tampered
   with.

2.  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].

3.  Validation

   Authorization data is highly sensitive and must be validated to
   insure no tampering has occured.

   In order to validate any information the receiving client need to be
   able to cryptographically verify the data.  This is done by
   introducing a new AuthorizationData element called AD-CAMMAC that
   contains enough information to bind the contents to a principal in a
   way that a receiving client can verify autonomusly without further
   contact with the KDC.

   The following information is needed:

   o  The KDC signature.

   o  The Service Signature.

   o  Optional Trusted Service Key Signature.

   o  Optional PUBKEY KDC Signature.

   The KDC signature is required to allow the KDC to validate the data
   withouth requiring to recompute the contents at every TGS request.

   The SVC signature is required so that the Service can verify that the
   authorization data has been validated by the KDC.

   Both the Trusted Service Checksum and the asymmetric KDC Signature
   are useful to verify the authenticity of the contents on the same
   host, when the data is received by a less trusted service and passed

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   to a more trusted service on the same host without the need for
   additional roundtrips to the KDC.

   The ad-type for AD-CAMMAC is (TBD).

4.  Encoding

   The Kerberos protocol is defined in [RFC4120] using Abstract Syntax
   Notation One (ASN.1) [X680].  As such, this specification also uses
   the ASN.1 syntax for specifying both the abstract layout of the AD-
   CAMMAC attributes, as well as its encoding.

4.1.  AD-CAMMAC

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    AD-CAMMAC                   ::= SEQUENCE {
          kdc-signature         [0] Checksum,
          svc-signature         [1] Checksum,
          trusted-svc-signature [2] OPT-Checksum OPTIONAL,
          pubkey-signature      [3] TBD OPTIONAL,
          elements              [4] AuthorizationData
    }

    OPT-Checksum         ::= SEQUENCE {
          identifier     [0] PrincipalName,
          signature      [1] Checksum
    }

    kdc-signature
       A cryptographic checksum computed over the encoding of the
       elements field, keyed with the krbtgt key.
       Checksum type TBD.

    svc-signature
       A cryptographic checksum computed over the encoding of the
       elements field, keyed with the service long term key.
       Checksum type TBD.

    trusted-svc-signature
       A principal name and a cryptographic checksum computed over the
       encoding of the elements field, keyed with the long term key of
       the principal name specified in the Name field. Unless otherwise
       explicitly administratively configured, the key SHOULD be found
       by substituting the service name component of the principal name
       of the service with 'host'.
       If the service is 'host' this checksum is redundant and can be
       omitted.
       If the resulting host/<name>@REALM or the administratively
       configured service is not found in the KDC database this
       cheksum can be omitted.
       Checksum type TBD.

    pubkey-signature
       A name identifying the asymmetric key-pair used.
       A checksum computed over the encoding of the elements field using
       the Private Key identified in the Name field.
       If an asymmetric key is not available this checksum MUST be
       omitted.
       Signature type TBD.

    elements
       A sequence of authorization data elements issued by the KDC.

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5.  Assigned numbers

   TBD

6.  IANA Considerations

   TBD.

7.  Security Considerations

   Although generally authorization data are conveyed within a ticket
   and are thereby protected using the existing encryption methods on
   the ticket, some authorization data requires the additional
   protection provided by the CAMMAC.

8.  Acknowledgements

   TBD.

9.  References

9.1.  Normative References

   [RFC3961]  Raeburn, K., "Encryption and Checksum Specifications for
              Kerberos 5", RFC 3961, February 2005.

   [RFC3962]  Raeburn, K., "Advanced Encryption Standard (AES)
              Encryption for Kerberos 5", RFC 3962, February 2005.

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,
              July 2005.

9.2.  Informative References

   [MIT-Athena]
              Steiner, J., Neuman, B., and J. Schiller, "Kerberos: An
              Authentication Service for Open Network Systems. In
              Proceedings of the Winter 1988 Usenix Conference.
              February.", 1988.

   [RFC1510]  Kohl, J. and B. Neuman, "The Kerberos Network
              Authentication Service (V5)", RFC 1510, September 1993.

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

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [X.690]    ISO, "ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER) - ITU-T Recommendation
              X.690 (ISO/IEC International Standard 8825-1:1998)", 1997.

Appendix A.  Additional Stuff

   This becomes an Appendix.

Authors' Addresses

   Simo Sorce (editor)
   Red Hat

   Email: ssorce@redhat.com

   Tom Yu (editor)
   MIT Kerberos Consortium

   Email: tlyu@mit.edu

   Thomas Hardjono (editor)
   MIT Kerberos Consortium

   Email: hardjono@mit.edu

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