[e2e] where to put endpoint authentication?

Joe Touch touch at ISI.EDU
Fri May 7 11:24:29 PDT 2004

Hi, all,

The IETF TCPM mailing list has been discussing recent TCP RST spoofing 
attacks on BGP and how best to prevent those attacks.

I recently posted an Internet Draft that summarizes the issues, for 
context: draft-touch-anonsec-00.txt

During the writing of this draft, a question arose regarding the role of 
TCP's sequence number in authentication, and where best to place 
endpoint authentication. (see sections 3.1 and 4.1 in particular).

The question might be useful to raise here:

	1) should sequence numbers be used for authentication?

		IMO, the sequence space is primarily for:
			1. receiver reordering
			2. congestion control
			3. duplicate detection

		TCP drops segments outside the receive window
		primarily, IMO, to discard stale segments

		draft-tcpm-tcpsecure narrows the valid receive
		window for RST segments (allowing them only
		at the end of the current receive window),
		primarily to protect against off-path RST
		spoofing attacks

		there have been previous suggestions to increase
		the TCP sequence space to 64 bits, being revisited
		to see if the additional 32 bits can provide the
		equivalent of a segment 'cookie'

	2) do transport protocols need authentication?

		current transport authentication - cookies, MD5
		signatures, etc., protect against off-path spoofing

		such spoofing relies on forgery of several values:
			- IP source/dest addresses
			- TCP ports/sequence numbers

		such attacks can be considered either:
			- primarily network forgery
			- forgery at both network and transport layers

		where is protection more appropriate/useful?
			- network (IMO)
			- transport
			- both are needed

	3) are cookies reasonable authentication for transport layers?

Thoughts, either privately or to this list, appreciated. Additional 
comments have been circulating on the IETF TCPM, IPsec, and MOBIKE 
mailing lists, FYI.

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