RFC 4304

Network Working Group RFC 4304 ✨ Extended Sequence Number (ESN) Addendum to IPsec DOI for ISAKMP 🎀

okay bestie, let's get into it 💖 This one is by Stephen Kent of BBN Technologies 🦋, filed in December 2005, and it's a Standards Track doc 👑. It's an addendum to the IPsec Domain of Interpretation for ISAKMP, and it does not obsolete anything and does not update anything 💅. It's a brand-new add-on, no drama.

Status of This Memo 🌸

okay so this one is an Internet standards track protocol for the Internet community 🫶. It's asking for discussion and suggestions for improvements, and you should check the "Internet Official Protocol Standards" (STD 1) for the current standardization state and status of this protocol 📚. Distribution of this memo is unlimited, so share away 💜.

Copyright Notice 🌈

Copyright (C) The Internet Society (2005) ✨.

Abstract 🧚

ngl the whole point here is replay detection 😭. The IP Security Authentication Header (AH) and Encapsulating Security Payload (ESP) protocols use a sequence number to catch replays 🔁. This doc extends the IPsec DOI for ISAKMP so you can negotiate whether an AH or ESP security association uses the traditional 32-bit sequence numbers or the extended (64-bit) sequence numbers (ESNs) 🍓. Iconic energy ✨.

1. Introduction 🎀

So AH and ESP both have an option for extended (64-bit) sequence numbers 💅. Why do we want it? Because it lets you send huge amounts of data at high speed over an IPsec Security Association without having to rekey just to dodge running out of sequence number space 🔥. This doc adds what the IPsec DOI for ISAKMP [DOI] needs so you can negotiate the ESN option 🦋.

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they show up in this document, are to be read as described in RFC 2119 [Bra97] 💜. Those capitalized words are the ones that really matter, so read them like they're underlined in red 🙈.

2. IPsec Security Association Attribute 🌸

This SA attribute is used in Phase II of an Internet Key Exchange Protocol (IKE) negotiation 🔐. The attribute type is Basic (B) ✨. How it gets encoded is defined in the base ISAKMP specification [ISAKMP]. Attributes that are basic MUST NOT be encoded as variable, so don't even try 🙅‍♀️. For more on attribute encoding in the IPsec DOI, check [IKE] 📖. And every restriction listed in [IKE] also applies to the IPsec DOI and to this addendum 💖.

Attribute Type 🦋

          class                        value           type
   ---------------------------------------------------------
   Extended (64-bit) Sequence Number    11              B

Class Values 🍓

This class says the Security Association will be using 64-bit sequence numbers 💅. (See [AH] and [ESP] for a description of extended (64-bit) sequence numbers.)

   RESERVED                0
   64-bit Sequence Number  1

3. Attribute Negotiation 🔥

Okay, so if an implementation gets a defined IPsec DOI attribute (or attribute value) that it doesn't support, it SHOULD send an ATTRIBUTES-NOT-SUPPORT, and the security association setup MUST be aborted 🙈.

Wait, also: if an implementation receives any attribute value other than the one for 64-bit sequence numbers, the security association setup MUST be aborted 💀.

4. Security Considerations 💀

This memo is about the Internet Key Exchange protocol [IKE], which combines ISAKMP [ISAKMP] and Oakley [OAKLEY] to derive cryptographic keying material in a secure and authenticated way 🔐. Specific discussion of the various security protocols and transforms in this document lives in the associated base documents and the cipher references 📚.

The addition of the ESN attribute does not change the underlying security characteristics of IKE 💅. But when you use ESNs with ESP, it's super important to use an encryption mode that stays secure when very large volumes of data are encrypted under one key 😭. So, for example, Data Encryption Standard (DES) in Cipher Block Chaining (CBC) mode would NOT be suitable for use with the ESN 🚫, because no more than 2^32 blocks should be encrypted under a single DES key in that mode 💀. Similarly, the integrity algorithm used with ESP or AH should be secure relative to the number of packets being protected 🛡️. To avoid potential security problems from algorithm limits, the SA lifetime MAY be set to limit how much data gets protected with a single key, before you hit the 2^64 packet limit that ESN imposes 🧚.

5. IANA Considerations 🌈

This document contains a "magic" number to be maintained by the IANA ✨. No additional class values will be assigned for this attribute 🙅‍♀️. The IANA has allocated an IPsec Security Attribute value for "Attribute Type" 🎀, and you can find it under the heading "value" in the table in Section 2 💖.

Acknowledgements 🫶

The author would like to thank the members of the IPsec working group 💜. The author also acknowledges Karen Seo for her help editing this spec 🌸.

Normative References 📚

[Bra97]  Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Level", BCP 14, RFC 2119, March 1997.

[AH]     Kent, S., "IP Authentication Header", RFC 4302, December
         2005.

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

[ESP]    Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
         4303, December 2005.

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

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

Informative References 🧚

[OAKLEY] Orman, H., "The OAKLEY Key Determination Protocol", RFC
         2412, November 1998.

Author's Address 🦋

Stephen Kent BBN Technologies 10 Moulton Street Cambridge, MA 02138 USA

Phone: +1 (617) 873-3988 EMail: kent@bbn.com

Full Copyright Statement 💅

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

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Acknowledgement 💖

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