Re: [Lake] Forward Security with PSK-Only LAKE
Karthik Bhargavan <karthikeyan.bhargavan@inria.fr> Fri, 17 January 2020 10:58 UTC
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Subject: Re: [Lake] Forward Security with PSK-Only LAKE
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It looks like I over-simplified the protocol. Some clarifications and corrections below. At the beginning of a session: A and B have a PSK K, associated with id I, and a session counter C --- A -> B: m1 = N_A, I, C, other_params B -> A: m2 = N_B, other_params, MAC(K_mB, m1 | m2) A -> B: MAC(K_mA, m1 | m2) A -> B: AEAD(K_eA, msg0,…) B -> A: AEAD(K_eB, msg1,…) —— At the end of a session: A and B set C <- C + 1, K <- HKDF(K, I, C+1) A and B throw away the old PSK K. Note: - N_A and N_B are nonces generated by A and B, respectively. - K_mA = HKDF(K, “mac_key A”, m1 | m2) - K_mB = HKDF(K, “mac_key B”, m1 | m2) - K_eA = HKDF(K, “ae_key A”, m1 | m2) - K_eB = HKDF(K, “ae_key B”, m1 | m2) > > -------- > > The above protocol can be generalized in several ways. > First, A and B need not have exactly the same counter C, instead they could negotiate the MAX of their two counters and derive the PSK corresponding to that counter. > Second, A and B may share both a long-term PSK K0 and an ephemeral PSK K and mix them both together in the protocol above. > This provides a clean separation between the PSK used for authentication and the PSK used for forward secrecy. > Third, we may use the protocol above as a “fast resumption” mechanism but fall back to full PSK-ECDHE whenever we want. > > To conclude, I wonder if we should explicitly consider a mechanism like the above as a requirement for LAKE. > It appears to meet the security goals we have set for PSK-LAKE and it is a good example of what can be achieved without an expensive DH operation. > (Incidentally, the message sizes of the protocol above are very tiny.) > > -Karthik > > > > > -- > Lake mailing list > Lake@ietf.org > https://www.ietf.org/mailman/listinfo/lake
- [Lake] Forward Security with PSK-Only LAKE Karthik Bhargavan
- Re: [Lake] Forward Security with PSK-Only LAKE Karthik Bhargavan
- Re: [Lake] Forward Security with PSK-Only LAKE Eric Rescorla
- Re: [Lake] Forward Security with PSK-Only LAKE Benjamin Beurdouche
- Re: [Lake] Forward Security with PSK-Only LAKE Karthik Bhargavan
- Re: [Lake] Forward Security with PSK-Only LAKE Benjamin Beurdouche
- Re: [Lake] Forward Security with PSK-Only LAKE Benjamin Beurdouche
- Re: [Lake] Forward Security with PSK-Only LAKE Karthik Bhargavan
- Re: [Lake] Forward Security with PSK-Only LAKE John Mattsson
- Re: [Lake] Forward Security with PSK-Only LAKE Göran Selander