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A TCP Authentication Option Extension for Payload Encryption
draft-touch-tcp-ao-encrypt-00

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Author Dr. Joseph D. Touch
Last updated 2014-03-19
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draft-touch-tcp-ao-encrypt-00
TCPM WG                                                        J. Touch
Internet Draft                                                  USC/ISI
Intended status: Standards Track                         March 19, 2014
Expires: September 2014

       A TCP Authentication Option Extension for Payload Encryption
                     draft-touch-tcp-ao-encrypt-00.txt

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   This Internet-Draft is submitted in full conformance with the
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   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Abstract

   This document describes an extension to the TCP Authentication
   Option (TCP-AO) to encrypt the TCP segment payload in addition to
   providing TCP-AO's authentication of the payload, TCP header, and IP
   pseudoheader. This extension changes how the packet contents and
   headers are processed and which keys are derived, but not its key
   coordination or protection of long-lived connections.

Table of Contents

   1. Introduction...................................................2
   2. Conventions used in this document..............................3
   3. Background.....................................................3
   4. Extension for Payload Encryption...............................3
      4.1. Additional Master Key Tuple components....................3
      4.2. Additional traffic keys...................................4
      4.3. Per-Connection TCP-AO Parameters..........................4
      4.4. Traffic Encryption Key Derivation Functions...............4
   5. TCP-AO-ENC Interaction with TCP................................5
      5.1. Sending TCP Segments......................................5
      5.2. Receiving TCP Segments....................................5
      5.3. Other TCP Impact..........................................5
   6. Security Considerations........................................5
   7. To be completed................................................6
   8. IANA Considerations............................................6
   9. References.....................................................6
      9.1. Normative References......................................6
      9.2. Informative References....................................6
   10. Acknowledgments...............................................7

1. Introduction

   This document describes an extension to the TCP Authentication
   Option (TCP-AO) [RFC5925] called TCP-AO-ENC to support its use to
   encrypt TCP segment payload contents in addition to authenticating
   the segment. TCP-AO-ENC is intended for use where TCP user data
   privacy is required and where TCP control protocol protection is
   also needed.

   This document assumes detailed familiarity with TCP-AO [RFC5925].
   TCP-AO-ENC extends how TCP-AO generates traffic keys and how those

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   keys are used to process TCP segment headers and payloads, but does
   not otherwise alter the TCP-AO mechanism [RFC5926].

2. Conventions used in this document

   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 RFC-2119 [RFC2119].
   When used in lower case, these words have their conventional meaning
   and do not convey the interpretations in RFC-2119.

3. Background

   The premise of TCP-AO-ENC is that it might be useful to allow TCP-AO
   to encrypt TCP segment payloads, in addition to authenticating the
   entire segment.

   This is accomplished by the following additions, as a preview:

   o  An encryption flag to indicate when segment payload encryption is
      used.

   o  Traffic encryption key, in addition to the TCP-AO traffic
      (authentication) key. TCP-AO-ENC can be used with only symmetric
      ciphers that avoiding the need for padding (stream ciphers).

   o  Augment input and output processing to include
      encryption/decryption.

   TCP-AO-ENC does not change any other aspects of TCP-AO [RFC5925],
   and is compatible with TCP-AO-NAT [RFC6978]. TCP-AO-NAT is intended
   for use only where coordinated between endpoints for connections
   that match the shared MKT parameters, as with all other MKT
   parameters.

4. Extension for Payload Encryption

   The following describe the additions to TCP-AO needed to support
   TCP-AO-ENC.

4.1. Additional Master Key Tuple components

   TCP-AO-ENC augments the MKT as follows; as with other MKT
   components, these MUST NOT change during a connection:

   o  TCP encryption flag.  When present, this indicates the use of
      segment payload encryption.

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   o  Encryption Key Derivation Function (E-KDF).  Indicates the key
      derivation function and its parameters, as used to generate
      traffic encryption keys from master keys in the same way that the
      TCP-AO KDG generates traffic (authentication) keys.

   o  Encryption algorithm.  Indicates the encryption algorithm and its
      parameters as used for encrypted connections.

   PTCP-AO-ENC processes TCP packets in the same way as TCP-AO, except
   that it replaces the authentication input and output processing as
   follows:

4.2. Additional traffic keys

   TCP-AO-ENC uses the E-KDF to derive four additional keys used for
   traffic encryption:

   o  Send_SYN_traffic_encryption_key

   o  Receive_SYN_traffic_encryption_key

   o  Send_other_traffic_encryption_key

   o  Receive_other_traffic_encryption_key

4.3. Per-Connection TCP-AO Parameters

   The per-connection TCP-AO parameters are not affected by the use of
   TCP-AO-ENC, except that MKTs indicated by Current_key and Rnext_key
   would indicate the use of payload encryption.

   The use of payload encryption as specified in these MKTs SHOULD NOT
   change during a TCP connection.

4.4. Traffic Encryption Key Derivation Functions

   Traffic encryption keys are derived from the MKTs using the E-KDF,
   in the same way and used on the same segments as their corresponding
   authentication keys, e.g.:

   o  Send_SYN_traffic_encryption_key / Send_SYN_traffic_key

   o  Receive_SYN_traffic_encryption_key / Receive_SYN_traffic__key

   o  Send_other_traffic_encryption_key / Send_other_traffic__key

   o  Receive_other_traffic_encryption_key / Receive_other_traffic_key

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5. TCP-AO-ENC Interaction with TCP

   TCP-AO-ENC augments TCP segment send and receive processing to
   include encryption/decryption. Note that the encryption
   initialization vector MAY depend on TCP header state, but MUST NOT
   depend on the processing of previous segments because segments may
   arrive (and need to be decrypted) out of order.

5.1. Sending TCP Segments

   Outgoing TCP segments are processed as follows:

   1. The segment payload is encrypted in-place using the traffic
      encryption key.

   2. The segment is authenticated using TCP-AO as per [RFC5925].

5.2. Receiving TCP Segments

   Incoming TCP segments are processed as follows:

   1. TCP-AO authenticates the segment, including discarding it if
      authentication fails, as per [RFC5925].

   2. The segment payload is decrypted in-place using the traffic
      encryption key.

5.3. Other TCP Impact

   TCP-AO-ENC has no impact on TCP beyond that of TCP-AO, including
   impact on TCP header size, connectionless resets, and ICMP handling.

   TCP-AO-ENC is compatible with the use of TCP-AO-NAT if traversal of
   NAT boxes is desired.

6. Security Considerations

   TCP-AO-ENC augments TCP-AO to provide segment payload privacy.

   TCP-AO-ENC relies on TCP-AO's authentication to avoid replay attacks
   and to ensure that the segments originate from the intended source.

   TCP-AO-ENC supports only stream ciphers because the TCP segment must
   be encrypted and decrypted in-situ. Support for padding would
   require additional option space to indicate the original message
   length, and this complication does not seem necessary.

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   The design of TCP-AO-ENC can support either symmetric or asymmetric
   keys. However, because TCP-AO derives traffic (authentication) keys
   from MKTs using KDFs, it was deemed sufficient that TCP-AO-ENC
   derive traffic encryption keys from MKTs using E-KDFs in a similar
   manner, and both endpoints would thus derive the same traffic
   encryption keys just as they derive the same traffic
   (authentication) keys. Extensions of TCP-AO-ENC to support
   asymmetric keying are possible if traffic keys are managed using an
   out-of-band mechanism, but not if they are derived from MKTs.

7. To be completed...

   Where are required algorithms specified? This doc or a separate one?

   o  E-KDF - also, can a MKT use the same alg for KDF and E-KDF?

   o  Encryption algorithm - possibilities include AES CTR (CTR initial
      value can be the ESN) or AES CBC and Camellia CBC as per TLS 1.2.

8. IANA Considerations

   (TO BE CONFIRMED, BUT FOR NOW:)

   There are no IANA considerations for this document. This section can
   be removed upon publication as an RFC.

9. References

9.1. Normative References

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

   [RFC5925] Touch, J., A. Mankin, R. Bonica, "The TCP Authentication
             Option", RFC 5925, Jun. 2010.

   [RFC5926] Lebovitz, G., E. Rescorla, "Cryptographic Algorithms for
             the TCP Authentication Option (TCP-AO)", RFC 5926, June
             2010.

9.2. Informative References

   [RFC6978] Touch, J., "A TCP Authentication Option Extension for NAT
             Traversal", RFC 6978, July 2013.

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10. Acknowledgments

   This extension was informed by discussions with Gene Tsudik.

   This document was prepared using 2-Word-v2.0.template.dot.

Author's Address

   Joe Touch
   USC/ISI
   4676 Admiralty Way
   Marina del Rey, CA 90292
   USA

   Phone: +1 (310) 448-9151
   Email: touch@isi.edu

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