Subject: [IPsec] Replay Protection

From: Venkatesh Sriram <[email-masked]>
Date: Tue, 2 Feb 2010 06:15:40 +0530

Hi,

Most IETF documents state that replay protection is not provided with
manual keying. I wanted to understand the reason for the same. Is it
because with manual keying there is no way to negotiate the sequence
numbers and thus provision for replay protection is not supported?

Thanks,
Sriram

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From: Dan McDonald <[email-masked]>
Date: Mon, 01 Feb 2010 19:58:32 -0500

> numbers and thus provision for replay protection is not supported?

You *could* enforce replay protection on manually added SAs, but with the
restrictions that:

	- Both SAs must be kept in sync at all times.  Reboots, or other
          expiration events, will not be able to kick any
          key-management-protocol (e.g. IKE) in the pants to get new SAs.

	- SAs MUST be unicast.  There's no easy-to-secure way to share replay
          state across a multi-receiver or multi-sender SA.

Programming interfaces to the SADB (like PF_KEY) or manual-keying programs
(like setkey(8) on BSD or ipseckey(1M) on OpenSolaris) might be able to allow
a manually-keyed SA with replay protection, but without the above operational
restrictions, things would break down quickly.  This is why most manual key
programs do not enable replay protection on an SA by default.

Hope this helps,
Dan

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From: Venkatesh Sriram <[email-masked]>
Date: Tue, 2 Feb 2010 06:39:28 +0530

> programs do not enable replay protection on an SA by default.

It does. Thank You!

Sriram

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From: Steven Bellovin <[email-masked]>
Date: Mon, 1 Feb 2010 20:09:48 -0500

> numbers and thus provision for replay protection is not supported?

And in particular, after a reboot you've lost all knowledge of your sequence number space.  (This has been a real issue for WEP; see http://www.cs.berkeley.edu/~daw/papers/wep-mob01.ps)

		--Steve Bellovin, http://www.cs.columbia.edu/~smb