Subject: [IPsec] NIST's Guidelines for secure deployment of IPv6

From: "Bhatia, Manav (Manav)" <[email-masked]>
Date: Wed, 4 Jan 2012 19:42:24 +0530

NIST has published the "Guidelines for secure deployment of IPv6" and it unequivocally says that AH has fallen out for ESP-NULL.

One can go through the document in detail. I have not gone through the entire document but here are some excerpts from that document:

(1) It says the following for OSPFv3:

"With routing protocols, routing integrity is usually a greater concern than confidentiality. The ESP 
parameter NULL indicating no encryption is generally regarded to be an acceptable choice for OSPF 
security."

(2) 4.2.4 Unresolved Aspects of IPv6 Multicast

"The security recommendations for PIM call for using IPsec AH, even for unicast messages.  Where IPsec 
is used with IPv4, AH has generally fallen out of use in favor of ESP, with NULL encryption when 
authentication-only is desired.  Thus the IPsec standard (RFC 4301) no longer requires AH, and many 
implementations omit it. See Section 5.3.6 for additional discussion of this topic."

(3) 5.3.1 Specification Overview

"Two security protocols: Authentication Header (AH) and Encapsulating Security 
Payload (ESP).  AH can provide integrity and replay protection for packet headers and data, 
but it cannot encrypt them.  ESP can provide encryption, integrity, and replay protection for 
packets, but it cannot protect the outermost IP header, as AH can.  This protection is not 
needed in most cases.  Accordingly, ESP is used much more frequently than AH because of its 
encryption capabilities, as well as other operational advantages.  The latest IPsec specification 
states that implementations MAY implement AH, and many choose not to.  For a VPN, which 
requires confidential communications, ESP is the natural choice."

And the below is the most interesting:

(4) 5.3.6 Unknown Aspects

"A debate exists over whether to use AH or ESP with NULL encryption for IPsec packets requiring
integrity protection but not confidentiality.  The standards themselves do not answer the question: IPv6 
standards tend to recommend or require AH, whereas IPsec standards have downgraded AH from MUST 
implement to MAY implement.  OSPFv3 originally specified AH, but this has been changed to ESPNULL.  
Some implementations only provide ESP.  AH has not been widely deployed.  (The common 
IPv4 applications of IPsec-VPNs and secure remote access-usually provide confidentiality, so this 
question does not arise.)  AH may also require more processing steps to compute or verify the integrity 
check value.  On the other hand, one of the main arguments in favor of AH is that it makes it easier for 
devices such as packet filtering routers, firewalls, and intrusion detection systems to recognize plaintext 
and examine packets (because ESP-NULL transmits plaintext but gives no visible indication that the 
payload is unencrypted).  As far as the cryptographic protection provided by AH versus ESP, it is difficult 
to discern any tangible difference when IPsec is used as intended.  In some cases, AH may protect certain 
vulnerable parts of the header or extension headers, but these cases are rare, and in these few cases, 
ESPNULL can achieve the same effect by being run in tunnel mode."

(5) 5.4.1 Using IPsec to Secure Autoconfiguration and ND

"AH was downgraded to MAY in RFC 4301 and is not included in many implementations."

Cheers, Manav

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From: Venkatesh Sriram <[email-masked]>
Date: Wed, 4 Jan 2012 21:12:09 +0530

Another document from NIST - Profile for IPv6 in the US Government
[1], lists AH as optional and ESP as mandatory.

It however says that if devices want to differentiate ESP NULL with
ESP encrypted traffic then they must use AH till the IPSecME WG comes
up with a mature standard that can easily do this. It says that if it
produces a mature RFC then the profile will be updated to recommend
its use. The version i have with me was published prior to WESP's
publication.

http://www.antd.nist.gov/usgv6/usgv6-v1.pdf

Sriram

[1] This document is meant to assist Federal agencies in formulating
plans for the acquisition of IPv6 technologies.

On Wed, Jan 4, 2012 at 7:42 PM, Bhatia, Manav (Manav)
<[email-masked]> wrote:
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