Internet Engineering Task Force                                  A. Jain
Internet-Draft                                              Georgia Tech
Intended status: Standards Track                               N. Kinder
Expires: March 1, 2015                                       N. McCallum
                                                           Red Hat, Inc.
                                                         August 28, 2014

              Authentication Indicator in Kerberos tickets


   This document proposes an extension in the Kerberos protocol.  It
   defines a new Authorization Data Type AUTHENTICATION-INDICATOR.  The
   purpose of introducing this data type is to include an indicator of
   the client's authentication strength in the service tickets so that
   the application services can use it as an input into policy

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 1, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Document Conventions  . . . . . . . . . . . . . . . . . . . .   2
   3.  AD Type Specification . . . . . . . . . . . . . . . . . . . .   2
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Kerberos allows secure interaction among users and services over a
   network.  It supports a variety of authentication mechanisms using
   its Pre-Authentication framework [RFC6113].  Kerberos Authentication
   Service has been architected to support password based authentication
   as well as multi-factor authentication using One Time Password
   devices or Public Key Cryptography.  Implementations that have Pre-
   Authentication mechanisms offering significantly different strengths
   of client authentication may choose to keep track of the strength of
   the authentication used as an input into policy decisions.  This
   document proposes a new Authorization Data Type to be used to convey
   the authentication strength to the application services.  The AD type
   is wrapped in the AD-CAMMAC [I-D.ietf-krb-wg-cammac] container and
   contains information about the type of authentication mechanism used
   by the Kerberos client to authenticate itself to the KDC.

2.  Document Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  AD Type Specification

   The KDC MAY include the following Authorization Data element, wrapped
   in AD-CAMMAC, in the initial credentials and copy it from a ticket-
   granting ticket into service tickets:


   The corresponding ad-data field contains the DER encoding of this AD
   type which is defined as

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   These values are short strings that indicate that a particular set of
   requirements was met during the initial authentication.  These
   strings are intended to be compared against known values.  They are
   not intended to store structured data.  These strings MAY be site-
   defined strings that do not contain a colon such as the name of the
   Pre-Authentication mechanism used, or alternatively URIs that
   reference a Level of Assurance Profile [RFC6711].

   The AUTHENTICATION-INDICATOR AD type MUST be included in the AD-
   CAMMAC container so that its contents can be protected.  The AD-
   CAMMAC element and the new AD type it encapsulates MAY safely be
   ignored by the applications and KDCs that do not implement this

4.  Security Considerations

   AUTHENTICATION-INDICATOR is wrapped in AD-CAMMAC which supersedes AD-
   KDC-ISSUED container.  AD-CAMMAC allows both the application service
   and the KDC to verify the authenticity of the contained Authorization

   A malicious service can replace AD-CAMMAC in a service ticket with a
   legitimate AD-CAMMAC present in some other ticket that the service
   has received.  KDC MUST ensure that the service does not tamper with
   the contents of AD-CAMMAC or the ticket.  It SHOULD insert an
   Authorization Data element into the AD-CAMMAC container that binds
   the contents of the container to the enclosing ticket.  This binding
   protects AUTHENTICATION-INDICATOR in case of constrained delegation
   such as S4U2Proxy [MS-SFU] extension.

   Using multiple strings in AUTHENTICATION-INDICATOR MAY lead to
   ambiguity when a service tries to make a decision based on the
   AUTHENTICATION-INDICATOR values.  This ambiguity can be avoided if
   indicator values are always used as a positive indication of certain
   requirements being met during the initial authentication.

5.  References

5.1.  Normative References

              Sorce, S., Yu, T., and T. Hardjono, "Kerberos
              Authorization Data Container Authenticated by Multiple
              MACs", draft-ietf-krb-wg-cammac-08 (work in progress),
              June 2014.

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

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

   [RFC6113]  Hartman, S. and L. Zhu, "A Generalized Framework for
              Kerberos Pre-Authentication", RFC 6113, April 2011.

5.2.  Informative References

   [MS-SFU]   Microsoft, "Kerberos Protocol Extensions: Service for User
              and Constrained Delegation Protocol", January 2013,

   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism: Version 2", RFC 4121, July

   [RFC6711]  Johansson, L., "An IANA Registry for Level of Assurance
              (LoA) Profiles", RFC 6711, August 2012.

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Appendix A.  Acknowledgements

   Dmitri Pal (Red Hat)
   Simo Sorce (Red Hat)

Authors' Addresses

   Anupam Jain
   Georgia Tech
   225 North Ave NW
   Atlanta, GA  30332


   Nathan Kinder
   Red Hat, Inc.
   444 Castro St.
   Suite 500
   Mountain View, CA  94041


   Nathaniel McCallum
   Red Hat, Inc.
   100 East Davie Street
   Raleigh, NC  27601


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