Internet Engineering Task Force                                  A. Jain
Internet-Draft                                              Georgia Tech
Updates: 4120 (if approved)                                    N. Kinder
Intended status: Standards Track                             N. McCallum
Expires: August 21, 2015                                   Red Hat, Inc.
                                                       February 17, 2015

              Authentication Indicator in Kerberos Tickets


   This document proposes an extension in the Kerberos protocol
   [RFC4120].  It defines a new Authorization Data Type AD-
   AUTHENTICATION-INDICATOR.  The purpose of introducing this data type
   is to include an indicator of the strength of a client's
   authentication in the service tickets so that the application
   services can use it as an input into policy decisions.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 21, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   to this document.  Code Components extracted from this document must

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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   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 [RFC4120] allows secure interaction among users and services
   over a network.  It supports a variety of authentication mechanisms
   using its Pre-Authentication framework [RFC6113].  The 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-kitten-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:


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   The corresponding ad-data field contains the DER encoding of the
   ASN.1 type which is defined as


   Each UTF8String value is a short string that indicates 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

   container so that its contents can be protected.  The AD-
   AUTHENTICATION-INDICATOR MAY safely be ignored by the applications
   and KDCs that do not implement this element.

4.  Security Considerations

   AD-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 Data.

   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.  The KDC MUST ensure that the service does not tamper
   with the contents of AD-CAMMAC or the ticket by including a kdc-
   verifier in the containing CAMMAC.  This binding protects AD-
   AUTHENTICATION-INDICATOR in case of constrained delegation such as
   S4U2Proxy [MS-SFU] extension.

   Using multiple strings in AD-AUTHENTICATION-INDICATOR MAY lead to
   ambiguity when a service tries to make a decision based on the AD-
   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

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              Sorce, S., Yu, T., and T. Hardjono, "Kerberos
              Authorization Data Container Authenticated by Multiple
              MACs", draft-ietf-kitten-cammac-01 (work in progress),
              January 2015.

   [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,

   [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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