


Network Working Group                               L. Hornquist Astrand
Internet-Draft                                               Apple, Inc.
Intended status: Standards Track                              S. Hartman
Expires: February 14, 2009                        Painless Security, LLC
                                                         August 13, 2008


                GSS-API: Delegate if approved by policy
                  draft-lha-gssapi-delegate-policy-00

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   Copyright (C) The IETF Trust (2008).













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Abstract

   Several GSS-API applications work in a multi-tiered architecture,
   where the server takes advantage of delegated user credentials to act
   on behalf of the user and contact additional servers.  In effect, the
   server acts as an agent on behalf of the user.  Examples include web
   applications that need to access e-mail or file servers as well as
   CIFs file servers.  However, delegating the ability to act as a user
   to a party who is not sufficiently trusted is problematic from a
   security standpoint.  Kerberos provides a flag called OK-AS-DELEGATE
   that allows the administrator of a Kerberos realm to communicate that
   a particular service is trusted for delegation.  This specification
   adds support for this flag and similar facilities in other
   authentication mechanisms to GSS-API (RFC 2743).


Table of Contents

   1.  Requirements Notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  GSS-API flag, c binding  . . . . . . . . . . . . . . . . . . .  5
   4.  GSS-API behavior . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  GSS-API behavior . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12























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1.  Requirements Notation

   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 [RFC2119].














































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2.  Introduction

   Several GSS-API applications work in a multi-tiered architecture,
   where the server takes advantage of delegated user credentials to act
   on behalf of the user and contact additional servers.  In effect, the
   server acts as an agent on behalf of the user.  Examples include web
   applications that need to access e-mail or file servers as well as
   CIFs file servers.  However, delegating the ability to act as a user
   to a party who is not sufficiently trusted is problematic from a
   security standpoint.

   Today, GSS-API [RFC2743] leaves the determination of whether
   delegation is desired to the client application.  If the client sets
   the deleg_req_flag to gss_init_sec_context then the application
   requests delegation.  This requires client applications to know what
   services should be trusted for delegation.  In some cases, however, a
   central authority is in a better position to know what services
   should receive delegation than the client application.  Some
   mechanisms such as Kerberos [RFC4121] have a facility to allow a
   realm administrator to communicate that a particular service is a
   valid target for delegation.  In Kerberos, the KDC can set the OK-AS-
   DELEGATE flag in issued tickets.  However even in such a case,
   delegating to services for applications that do not need delegation
   is problematic.  So, it is desirable for a GSS-API client to be able
   to request delegation if and only-if central policy reccomends
   delegation to the given target.

   This specification adds a new input flag to GSS_Init_sec_context to
   request delegation when approved by central policy.  In addition, a
   constant value to be used in the GSS-API C bindings [RFC2744] is
   defined.  Finally, the behavior for the Kerberos mechanism [RFC4121]
   is specified.



















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3.  GSS-API flag, c binding

   The GSS_Init_sec_context API is extended to gain a new input flag: if
   the deleg_policy_req flag is set, then delegation should be performed
   if recommended by central policy.  In addition, the C bindings are
   extended to define the following constant to represent this new flag.



   #define GSS_C_DELEG_POLICY_FLAG 32768









































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4.  GSS-API behavior

   As before, if the GSS_C_DELEG_FLAG is set, the GSS-API mechanism
   tries to delegate.  Output ret_flags contains the flag
   GSS_C_DELEG_FLAG if delegation is successful.

   If the GSS_C_DELEG_POLICY_FLAG is set, the code delegates only if the
   mechanism policy allows delegation.  If delegation is done, the
   output flag ret_flags contain both GSS_C_DELEG_FLAG and
   GSS_C_DELEG_POLICY_FLAG on the initator and GSS_C_DELEG_FLAG on the
   acceptor.

   If both GSS_C_DELEG_FLAG and GSS_C_DELEG_POLICY_FLAG are set, then
   delegation is attempted.  However GSS_C_DELEG_POLICY_FLAG is only set
   in ret_flags on the initiator if GSS_C_DELEG_POLICY_FLAG would have
   been sufficient to request delegation.



































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5.  GSS-API behavior

   If the GSS_C_DELEG_POLICY_FLAG is set, the Kerberos GSS-API mechanism
   will only delegate if ok-as-delegate is set [RFC4120] in the service
   ticket.  Other policy checks MAY be applied.














































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6.  Security Considerations

   Introduce a flag what allows client to get help from the KDC when to
   delegate to servers, will limit what servers that client delegate
   too.














































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7.  IANA Considerations

   This section needs to be revised to be consistent with the kitten
   IANA draft.















































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8.  Normative References

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

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC2744]  Wray, J., "Generic Security Service API Version 2 :
              C-bindings", RFC 2744, January 2000.

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

   [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 2005.
































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Authors' Addresses

   Love Hornquist Astrand
   Apple, Inc.

   Email: lha@apple.com


   Sam Hartman
   Painless Security, LLC

   Email: hartmans-ietf@mit.edu







































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