rfc2964.txt

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RFC 2964              Use of HTTP State Management          October 2000


   NOT be used as an authentication mechanism to protect information
   from being exposed to unauthorized parties, even if the HTTP sessions
   are encrypted.

   The prohibition against using HTTP State Management for
   authentication includes both its use to protect information which is
   provided by the service, and its use to protect potentially sensitive
   information about the user which is entrusted to the service's care.
   For example, it would be inappropriate to expose a user's name,
   address, telephone number, or billing information to a client that
   merely presented a cookie which had been previously associated with
   the user.

   Similarly, HTTP State Management SHOULD NOT be used to authenticate
   user requests if unauthorized requests might have undesirable side-
   effects for the user, unless the user is aware of the potential for
   such side-effects and explicitly consents to such use.  For example,
   a service which allowed a user to order merchandise with a single
   "click", based entirely on the user's stored "cookies", could
   inconvenience the user by requiring her to dispute charges to her
   credit card, and/or return the unwanted merchandise, in the event
   that the cookies were exposed to third parties.

   Some uses of HTTP State Management to identify users may be
   relatively harmless, for example, if the only information which can
   be thus exposed belongs to the service, and the service will suffer
   little harm from the exposure of such information.

3.  User Interface Considerations for HTTP State Management

   HTTP State Management has been very controversial because of its
   potential to expose information about a user's browsing habits to
   third parties, without the knowledge or consent of the user.  While
   such exposure is possible, this is less a flaw in the protocol itself
   than a failure of HTTP client implementations (and of some providers
   of HTTP-based services) to protect users' interests.

   As implied above, there are other ways to maintain session state than
   using HTTP State Management, and therefore other ways in which users'
   browsing habits can be tracked.  Indeed, it is difficult to imagine
   how the HTTP protocol or an HTTP client could actually prevent a
   service from disclosing a user's "click trail" to other parties if
   the service chose to do so.  Protection of such information from
   inappropriate exposure must therefore be the responsibility of the
   service.  HTTP client implementations inherently cannot provide such
   protection, though they can implement countermeasures which make it
   more difficult for HTTP State Management to be used as the mechanism
   by which such information is exposed.



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   It is arguable that HTTP clients should provide more protection in
   general against inappropriate exposure of tracking information,
   regardless of whether the exposure were facilitated by use of HTTP
   State Management or by some other means.  However, issues related to
   other mechanisms are beyond the scope of this memo.

3.1.  Capabilities Required of an HTTP Client

   A user's willingness to consent to use of HTTP State Management is
   likely to vary from one service to another, according to whether the
   user trusts the service to use the information appropriately and to
   limit its exposure to other parties.  The user therefore SHOULD be
   able to control whether his client supports a service's request to
   use HTTP State Management, on a per-service basis.  In particular:

   (1)   Clients MUST NOT respond to HTTP State Management requests
         unless explicitly enabled by the user.

   (2)   Clients SHOULD provide an effective interface which allows
         users to review, and approve or refuse, any particular requests
         from a server to maintain state information, before the client
         provides any state information to the server.

   (3)   Clients SHOULD provide an effective interface which allows
         users to instruct their clients to ignore all requests from a
         particular service to maintain state information, on a per-
         service basis, immediately in response to any particular
         request from a server, before the client provides any state
         information to the server.

   (4)   Clients SHOULD provide an effective interface which allows a
         user to disable future transmission of any state information to
         a service, and/or discard any saved state information for that
         service, even though the user has previously approved a
         service's request to maintain state information.

   (5)   Clients SHOULD provide an effective interface which allows a
         user to terminate a previous request not to retain state
         management information for a given service.

3.2.  Limitations of the domain-match algorithm

   The domain-match algorithm in RFC-2965 section 2 is intended as a
   heuristic to allow a client to "guess" whether or not two domains are
   part of the same service.  There are few rules about how domain names
   can be used, and the structure of domain names and how they are
   delegated varies from one top-level domain to another (i.e. the
   client cannot tell which part of the domain was assigned to the



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RFC 2964              Use of HTTP State Management          October 2000


   service).  Therefore NO string comparison algorithm (including the
   domain-match algorithm) can be relied on to distinguish a domain that
   belongs to a particular service, from a domain that belongs to
   another party.

   As stated above, each service is ultimately responsible for ensuring
   that user information is not inappropriately leaked to third parties.
   Leaking information to third parties via State Management by careful
   selection of domain names, or by assigning domain names to hosts
   maintained by third parties, is at least as inappropriate as leaking
   the same information by other means.

4.  Security Considerations

   This entire memo is about security considerations.

5.  Authors' Addresses

   Keith Moore
   University of Tennessee Computer Science Department
   1122 Volunteer Blvd, Suite 203
   Knoxville TN, 37996-3450

   EMail: [e-mail]


   Ned Freed
   Innosoft International, Inc.
   1050 Lakes Drive
   West Covina, CA 81790

   EMail: [e-mail]

6.  References

   [RFC 1123] Braden, R., "Requirements for Internet Hosts --
              Application and Support", STD 3, RFC 1123, October 1989.

   [RFC 2965] Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2965, October 2000.

   [RFC 2109] Kristol, D. and L. Montulli, "HTTP State Management
              Mechanism", RFC 2109, February 1997.








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7.  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.



















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