Network Working Group                                           R. Glenn
Request for Comments: 2410                                          NIST
Category: Standards Track                                        S. Kent
                                                               BBN Corp
                                                          November 1998


         The NULL Encryption Algorithm and Its Use With IPsec

Status of this Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

  This memo defines the NULL encryption algorithm and its use with the
  IPsec Encapsulating Security Payload (ESP).  NULL does nothing to
  alter plaintext data.  In fact, NULL, by itself, does nothing.  NULL
  provides the means for ESP to provide authentication and integrity
  without confidentiality.

  Further information on the other components necessary for ESP
  implementations is provided by [ESP] and [ROAD].

1.  Introduction

  This memo defines the NULL encryption algorithm and its use with the
  IPsec Encapsulating Security Payload [ESP] to provide authentication
  and integrity without confidentiality.

  NULL is a block cipher the origins of which appear to be lost in
  antiquity.  Despite rumors that the National Security Agency
  suppressed publication of this algorithm, there is no evidence of
  such action on their part. Rather, recent archaeological evidence
  suggests that the NULL algorithm was developed in Roman times, as an
  exportable alternative to Ceaser ciphers. However, because Roman
  numerals lack a symbol for zero, written records of the algorithm's
  development were lost to historians for over two millennia.





Glenn & Kent                Standards Track                     [Page 1]

RFC 2410                     NULL and IPsec                November 1998


  [ESP] specifies the use of an optional encryption algorithm to
  provide confidentiality and the use of an optional authentication
  algorithm to provide authentication and integrity.  The NULL
  encryption algorithm is a convenient way to represent the option of
  not applying encryption.  This is referred to as ESP_NULL in [DOI].

  The IPsec Authentication Header [AH] specification provides a similar
  service, by computing authentication data which covers the data
  portion of a packet as well as the immutable in transit portions of
  the IP header.  ESP_NULL does not include the IP header in
  calculating the authentication data.  This can be useful in providing
  IPsec services through non-IP network devices.  The discussion on how
  ESP_NULL might be used with non-IP network devices is outside the
  scope of this document.

  In this memo, NULL is used within the context of ESP.  For further
  information on how the various pieces of ESP fit together to provide
  security services, refer to [ESP] and [ROAD].

  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].

2. Algorithm Definition

  NULL is defined mathematically by the use of the Identity function I
  applied to a block of data b such that:

    NULL(b) = I(b) = b

2.1 Keying Material

  Like other modern ciphers, e.g., RC5 [RFC-2040], the NULL encryption
  algorithm can make use of keys of varying lengths.  However, no
  measurable increase in security is afforded by the use of longer key
  lengths.

2.2 Cryptographic Synchronization

  Because of the stateless nature of the NULL encryption algorithm, it
  is not necessary to transmit an IV or similar cryptographic
  synchronization data on a per packet (or even a per SA) basis.  The
  NULL encryption algorithm combines many of the best features of both
  block and stream ciphers, while still not requiring the transmission
  of an IV or analogous cryptographic synchronization data.






Glenn & Kent                Standards Track                     [Page 2]

RFC 2410                     NULL and IPsec                November 1998


2.3 Padding

  NULL has a block size of 1 byte, thus padding is not necessary.

2.4. Performance

  The NULL encryption algorithm is significantly faster than other
  commonly used symmetric encryption algorithms and implementations of
  the base algorithm are available for all commonly used hardware and
  OS platforms.

2.5 Test Vectors

  The following is a set of test vectors to facilitate in the
  development of interoperable NULL implementations.

test_case =      1
data =           0x123456789abcdef
data_len =       8
NULL_data =      0x123456789abcdef

test_case =      2
data =           "Network Security People Have A Strange Sense Of Humor"
data_len =       53
NULL_data =      "Network Security People Have A Strange Sense Of Humor"

3. ESP_NULL Operational Requirements

  ESP_NULL is defined by using NULL within the context of ESP.  This
  section further defines ESP_NULL by pointing out particular
  operational parameter requirements.

  For purposes of IKE [IKE] key extraction, the key size for this
  algorithm MUST be zero (0) bits, to facilitate interoperability and
  to avoid any potential export control problems.

  To facilitate interoperability, the IV size for this algorithm MUST
  be zero (0) bits.

  Padding MAY be included on outgoing packets as specified in [ESP].

4. Security Considerations

  The NULL encryption algorithm offers no confidentiality nor does it
  offer any other security service.  It is simply a convenient way to
  represent the optional use of applying encryption within ESP.  ESP
  can then be used to provide authentication and integrity without
  confidentiality.  Unlike AH these services are not applied to any



Glenn & Kent                Standards Track                     [Page 3]

RFC 2410                     NULL and IPsec                November 1998


  part of the IP header.  At the time of this writing there is no
  evidence to support that ESP_NULL is any less secure than AH when
  using the same authentication algorithm (i.e. a packet secured using
  ESP_NULL with some authentication algorithm is as cryptographically
  secure as a packet secured using AH with the same authentication
  algorithm).

  As stated in [ESP], while the use of encryption algorithms and
  authentication algorithms are optional in ESP, it is imperative that
  an ESP SA specifies the use of at least one cryptographically strong
  encryption algorithm or one cryptographically strong authentication
  algorithm or one of each.

  At the time of this writing there are no known laws preventing the
  exportation of NULL with a zero (0) bit key length.

5.  Intellectual Property Rights

  Pursuant to the provisions of [RFC-2026], the authors represent that
  they have disclosed the existence of any proprietary or intellectual
  property rights in the contribution that are reasonably and
  personally known to the authors.  The authors do not represent that
  they personally know of all potentially pertinent proprietary and
  intellectual property rights owned or claimed by the organizations
  they represent or third parties.

6.  Acknowledgments

  Steve Bellovin suggested and provided the text for the Intellectual
  Property Rights section.

  Credit also needs to be given to the participants of the Cisco/ICSA
  IPsec & IKE March 1998 Interoperability Workshop since it was there
  that the need for this document became apparent.

7.  References

  [ESP]        Kent, S., and R. Atkinson, "IP Encapsulating Security
               Payload", RFC 2406, November 1998.

  [AH]         Kent, S., and R. Atkinson, "IP Authentication Header",
               RFC 2402, November 1998.

  [ROAD]       Thayer, R., Doraswamy, N., and R. Glenn, "IP Security
               Document Roadmap", RFC 2411, November 1998.

  [DOI]        Piper, D., "The Internet IP Security Domain of
               Interpretation for ISAKMP", RFC 2408, November 1998.



Glenn & Kent                Standards Track                     [Page 4]

RFC 2410                     NULL and IPsec                November 1998


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

  [RFC-2026]   Bradner, S., "The Internet Standards Process -- Revision
               3", BCP 9, RFC 2026, October 1996.

  [RFC-2040]   Baldwin, R., and R. Rivest, "The RC5, RC5-CBC, RC5-CBC-
               Pad, and RC5-CTS Algorithms", RFC 2040, October 1996

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

6.  Editors' Addresses

  Rob Glenn
  NIST

  EMail: [email protected]


  Stephen Kent
  BBN Corporation

  EMail: [email protected]

  The IPsec working group can be contacted through the chairs:

  Robert Moskowitz
  ICSA

  EMail: [email protected]


  Ted T'so
  Massachusetts Institute of Technology

  EMail: [email protected]














Glenn & Kent                Standards Track                     [Page 5]

RFC 2410                     NULL and IPsec                November 1998


7.  Full Copyright Statement

  Copyright (C) The Internet Society (1998).  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.
























Glenn & Kent                Standards Track                     [Page 6]


You are viewing proxied material from gopher.rbfh.de. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.