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Versions: 00                                                            
IP Security Policy                                         M. Richardson
Internet-Draft                                                       SSW
Expires: October 15, 2006                                  B. Sommerfeld
                                                                     Sun
                                                          April 13, 2006


                     Requirements for an IPsec API
                  draft-ietf-btns-ipsec-apireq-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Given the open nature of the Internet today, application protocols
   require strong security.  IPsec's wire protocols appear to meet the
   requirements of many protocols.  The lack of a common model for
   application-layer interfaces has complicated use of IPsec by upper-
   layer protocols.  This document provides an overview of facilities
   which a host IPsec implementation should provide to applications to
   allow them to both observe and influence how IPsec protects their



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   communications.


Table of Contents

   1.    Motivation for this work . . . . . . . . . . . . . . . . . .  3
   2.    Terminology  . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.    Motivations for this work  . . . . . . . . . . . . . . . . .  3
   4.    Goals  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   5.    Requirements . . . . . . . . . . . . . . . . . . . . . . . .  4
   6.    System policy  . . . . . . . . . . . . . . . . . . . . . . .  4
   7.    HOW  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   8.    WHO  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   8.1.  OPAQUE IDENTITY  . . . . . . . . . . . . . . . . . . . . . .  5
   8.2.  AUDITING . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   8.3.  ACCESS CONTROL . . . . . . . . . . . . . . . . . . . . . . .  5
   8.4.  ATTRIBUTES/CREDENTIALS . . . . . . . . . . . . . . . . . . .  5
   9.    Error reporting  . . . . . . . . . . . . . . . . . . . . . .  6
   10.   Security Guarantees  . . . . . . . . . . . . . . . . . . . .  6
   10.1. Connection-oriented communication  . . . . . . . . . . . . .  6
   10.2. Connectionless communication . . . . . . . . . . . . . . . .  7
   11.   Non-goals And Bad Ideas  . . . . . . . . . . . . . . . . . .  7
   11.1. Exposure of keys . . . . . . . . . . . . . . . . . . . . . .  7
   11.2. Exposure of IPsec SPI values . . . . . . . . . . . . . . . .  7
   12.   Other issues . . . . . . . . . . . . . . . . . . . . . . . .  8
   13.   Security Considerations  . . . . . . . . . . . . . . . . . .  8
   14.   Document TODO  . . . . . . . . . . . . . . . . . . . . . . .  8
   15.   References . . . . . . . . . . . . . . . . . . . . . . . . .  8
   15.1. Normative References . . . . . . . . . . . . . . . . . . . .  8
   15.2. Informative References . . . . . . . . . . . . . . . . . . .  9
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
         Intellectual Property and Copyright Statements . . . . . . . 11



















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1.  Motivation for this work

   Many protocols under development are considering the use of IPsec for
   security.  Unfortunately, most existing IPsec implementations
   ([RFC2401] and [RFC4301]) do not give applications any visibility
   into what, if anything, they are doing on behalf of an application.
   This limitation only allows IPsec to do all-or-nothing access
   control, and requires two levels of authentication, with one within
   the application, and a second level within an IPsec key management
   protocol (most typically IKE [RFC2407][RFC2408][RFC2409] and IKEv2
   [RFC4306][RFC4307]).


2.  Terminology

   The term "socket" will be used here to identify an application-layer
   communications endpoint; it does imply any specific API is to be
   used.  For the purposes of this discussion, a socket may include:
      A communications endpoint for a connectionless protocol
      One end of an established connection for a connection-oriented
      protocol
      A listening endpoint for a connection-oriented protocol

   For the purposes of this document, the term "application" refers to
   programs implementing any client protocol using either IP or a
   transport protocol such as TCP or UDP running over IP.  Note that
   this is in many ways somewhat broader than the traditional use of
   "application" within the IETF, as it may also include
   "infrastructure" protocols built on top of IP and IPsec, including
   routing, ICMP, etc.


3.  Motivations for this work

   Most protocols for application security, such as TLS [RFC2246] and
   SSH [RFC4251] operate at or above the transport layer.  This renders
   the underlying transport connections vulnerable to denial of service
   attacks, including connection assassination [RFC3552].  IPsec offers
   the promise of protecting against many of these denial of service
   attacks.

   There are other potential benefits.  Conventional software-based
   IPsec implementations isolate applications from the cryptographic
   keys, improving security by making inadvertant or malicious key
   exposure more difficult.  In addition, specialized hardware may allow
   encryption keys protected from disclosure within trusted
   cryptographic units.  Also, custom hardware units may well allow for
   higher performance.



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   Areas where this is currently under active discussion include the set
   of block storage protocols being developed by the IP Storage working
   group [RFC3723] and NFS version 4 (XXX: need newer reference than
   target="I-D.ietf-nfsv4-ccm")


4.  Goals

   Separate policy and mechanism


5.  Requirements

   Here are some basic requirements for an IPsec application API:
      An application should be able to determine HOW a communication was
      protected (or not).
      An application should be able to determine WHO it is talking to.
      If a communication is nominally authorized but fails, an
      application should be able to get an indication of WHY it failed,
      to help identify the configuration error causing the spurious
      failure.
      An application should be able to influence HOW a communication is
      protected, subject to override or modification by system policy.
      An application should be able to indicate WHO it wishes to talk
      to, again subject to override or modification by system policy.
      These interfaces should be as independant as possible of the key
      management protocol being used; it should be possible to implement
      this with IKEv1, IKEv2, KINK, etc.,


6.  System policy

   Interactions with system policy:
      System-level policy trumps all
      By default, applications should be able to ask for *more*
      protection.
      Applications wishing *less* protection may need appropriate local
      privileges. (example: ike bypass of UDP port 500; DHCP lease
      renewals...)


7.  HOW

   An application may have requirements for confidentiality and/or
   integrity; it should be able to determine if an inbound communication
   was protected and whether an outbound communication will be
   protected.  In addition, there may well be a desire to express
   preferences for relative strength of algorithms, or specify the



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   specific algorithm to be used.  Hard-coding algorithm names into
   applications should be actively discouraged; perhaps there should be
   generic "weak" or "strong" indications instead of specific algorithm
   identifiers.


8.  WHO

   This is perhaps the most tricky part of the problem.  Existing IPsec
   key management protocols provide a wide variety of authentication
   methods -- preshared secrets, public key, Kerberos, X.509
   certificates, etc.,

   There are several potential uses for names provided by IPsec:

8.1.  OPAQUE IDENTITY

   It should be possible to determine that two IPsec-protected
   communications conducted within a short to medium time frame were
   with the same authenticated peer; it should be possible to use a
   received identity to initiate a communication back to that identity.

   Example cases: connectionless replies; linking ftp control and data
   connections.

   The application need only be able to determine if two identities are
   equal.

8.2.  AUDITING

   It should be possible for an application to construct a log entry
   naming the peer.

8.3.  ACCESS CONTROL

   While policy rules may allow traffic to be blocked entirely, it's
   often necessary for a program to provide services to mutually
   suspicious clients.  It should be possible for a service to make
   appropriate access control decisions based on the identity of the
   peer; in addition, the peer's certificate may contain interesting
   SubjectAltName or other attributes which may have relevance for the
   application; it may also be possible for the system to derive other
   attributes from the peer's identity.

8.4.  ATTRIBUTES/CREDENTIALS

   [Mission Creep Alert] In many cases, an application is not so much
   interested in the peer's name, but rather in some other attribute of



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   the peer.  Exactly where and how to map from long-term keys to these
   attributes needs to be nailed down; it may well be that this is best
   left as a local issue.

   Some of this is probably out of scope for the working group; however,
   we should not preclude others from building on this.


9.  Error reporting

   There are a number of reasons why a communication may fail because of
   IPsec configuration mismatches..

   These include, but are not limited to:
      Blocked by local or peer SPD.
      Local or peer key management protocols cannot establish an SA.
      Local or peer key management protocols cannot authenticate to each
      other.

   It MAY be appropriate to map IPsec failures into existing error codes
   (e.g., "connection refused", "connection timed out"), so that
   existing applications use appropriate error recovery strategies;
   however, this does result in a loss of information.  It SHOULD be
   possible for an IPsec-aware application to get additional information
   about the reasons that a communications failed.


10.  Security Guarantees

   Connection-oriented and connectionless communication often require
   different application structure.  In many case, it will often be most
   convenient to do security checks once per connection, while for
   connectionless communications, per-message operations will be needed.

10.1.  Connection-oriented communication

   Packet boundaries are not, in general, visible to clients of stream
   protocols such as TCP, while IPsec protection is provided (or not) on
   a packet-by-packet basis,

   In addition, it would be an unreasonable burden on applications to
   force them to continuously inquire about each individual packet.

   It should be possible for an application to ensure that all traffic
   to a particular socket is protected appropriately; it should also be
   possible for an application to ensure that all traffic to a socket
   originates from the same authenticated identity.




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   A pair of communicating applications should be able to determine that
   the ipsec protection on a connection between them is end-to-end.

   Note that it is common for datagram socket API's to allow a "connect"
   operation which sets a default destination and filters inbound
   packets based on source address; it should similarly be possible for
   the connection-oriented security guarantees to be applied to datagram
   sockets being used for 1:1 communications.

10.2.  Connectionless communication

   It is also common to use datagram sockets for many-to-many
   communication; it should be possible to get and set identity
   information on a packet-by-packet basis.

   It may well be the case that a datagram-oriented client application
   will use the connection-oriented part of this API (because it is
   using a given datagram socket to talk to a specific server) while the
   server it is talking to use the connectionless API because it is
   using a single socket to receive requests from and send replies to a
   large number of clients.


11.  Non-goals And Bad Ideas

   Here are a few ideas which have popped up every so often which really
   seem to be bad ideas.. in other words, things which should not be
   exposed to applications because they can't be used reliably or which
   cause active harm.

11.1.  Exposure of keys

   There is absolutely no reason for applications to see the underlying
   encryption keys, or influence the choice of keys.  This is to allow
   an IPsec implementation to have a clear boundary around its
   cryptographic components.

11.2.  Exposure of IPsec SPI values

   In general, there is no need for applications to see SPI values or
   keys; it's also the case that in many cases the exact algorithm used
   may not be of interest as long as it is appropriately strong.

   Since both IKE and IPsec SA's may be short-lived, it is plausible
   that:
      an application connection or association will outlive any given
      IPsec SA.
      an application connection or association will outlive any given



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      IKE SA.
      an application connection may be idle for extended periods, during
      which time there is no IKE or IPsec SA state between the peers.
   It should be the case that any properties provided to applications
   regarding peer identity, protection, etc., should be able to survive
   rekeying.

   It may be appropriate to use SPI values as temporary handles, but
   applications may last much longer than SA's, and SPI values may be
   recycled over time; it would be better for there to be a separate,
   local-use-only, space for (identity, params) pairs.


12.  Other issues

      Interface-specific vs. application-specific policy; deal with this
      as separate layers of filtering/intersections/etc?
      Real-time notifications of both ends that rekey, etc., is having
      trouble (highly desirable for VoIP-type applications).
      Balancing keeping full certificate handling out of applications
      while still providing full access to certificate attributes.


13.  Security Considerations


14.  Document TODO

      Flesh out Other Issues section.
      Flesh out Informative References with references to existing
      IPsec-related API's
      Improve security considerations section.


15.  References

15.1.  Normative References

   [RFC2407]  Piper, D., "The Internet IP Security Domain of
              Interpretation for ISAKMP", RFC 2407, November 1998.

   [RFC2408]  Maughan, D., Schneider, M., and M. Schertler, "Internet
              Security Association and Key Management Protocol
              (ISAKMP)", RFC 2408, November 1998.

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.




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   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

   [RFC4307]  Schiller, J., "Cryptographic Algorithms for Use in the
              Internet Key Exchange Version 2 (IKEv2)", RFC 4307,
              December 2005.

15.2.  Informative References

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2401]  Kent, S. and R. Atkinson, "Security Architecture for the
              Internet Protocol", RFC 2401, November 1998.

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

   [RFC3723]  Aboba, B., Tseng, J., Walker, J., Rangan, V., and F.
              Travostino, "Securing Block Storage Protocols over IP",
              RFC 3723, April 2004.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.























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Authors' Addresses

   Michael C. Richardson
   Sandelman Software Works
   470 Dawson Avenue
   Ottawa, ON  K1Z 5V7
   CA

   Email: mcr@sandelman.ottawa.on.ca
   URI:   http://www.sandelman.ottawa.on.ca/


   Bill Sommerfeld
   Sun Microsystems
   1 Network Drive
   Burlington, MA  01803
   US

   Phone: +1 781 442 3458
   Email: somerfeld@sun.com































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