Re: [tcpm] tcp-auth-opt issue: unique connection keys
Joe Touch <touch@ISI.EDU> Thu, 31 July 2008 09:04 UTC
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Date: Thu, 31 Jul 2008 02:03:21 -0700
From: Joe Touch <touch@ISI.EDU>
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To: Eric Rescorla <ekr@networkresonance.com>
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Subject: Re: [tcpm] tcp-auth-opt issue: unique connection keys
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Eric Rescorla wrote: ... |> The differences in the alternatives discussed so far: |> |> A- precomputed keys |> require additional per-connection key storage space |> |> B- on-the-fly |> 1- if ISN is hashed into the key used for a packet, |> this requires an additional full MAC computation |> per packet |> |> 2- if ISN is prepended to the data, this requires |> a longer MAC computation ... | I must be missing something. Our job is to specify what bits go | into the MAC. Why do we have to specify when these computations | are done beyond that? It seems like implementations should be | allowed to make whatever time/space tradeoffs they feel are | most appropriate. In particular, why should we require one of | A and B(1), since they produce the same data on the wire? Point taken. So then it's between A/B1 and B2. | It's worth noting at this point that implementations of HMAC often | adopt the time/space tradeoff of precomputing the first round of HMAC | computations (to digest the keys) and using that instead of the key. | If you were working with prepending ISNs, you might also include | the ISNs in that state. When we talk about key storage, I would hope we aren't | precluding that sort of optimization. It depends on whether that precomputation is impacted by the use of ISNs in the MAC; that's the only reason there's an A/B1 vs. B2 difference noted above. How we specify the computation may affect whether it can be precomputed or needs storage/recomputation. We can jump up to the level of specifying the computation only (which allows implementation flexibility), but we need to know (AFAICT) the impact on these optimizations and whether we care... -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkiRfc8ACgkQE5f5cImnZruQXQCgrYHBO1g2LMIWMOpbUlqRD4bJ l8QAnA5UL8U4z16q/tpu5VxMt0hSue1e =tnZ4 -----END PGP SIGNATURE----- _______________________________________________ tcpm mailing list tcpm@ietf.org https://www.ietf.org/mailman/listinfo/tcpm
- [tcpm] tcp-auth-opt issue: unique connection keys Joe Touch
- Re: [tcpm] tcp-auth-opt issue: unique connection … Eric Rescorla
- Re: [tcpm] tcp-auth-opt issue: unique connection … Joe Touch
- Re: [tcpm] tcp-auth-opt issue: unique connection … Eric Rescorla
- Re: [tcpm] tcp-auth-opt issue: unique connection … Joe Touch
- Re: [tcpm] tcp-auth-opt issue: unique connection … Eric Rescorla
- Re: [tcpm] tcp-auth-opt issue: unique connection … Joe Touch