IACR News item: 02 February 2016
Christina Brzuska, Håkon Jacobsen, Douglas Stebila
ePrint Report
We investigate how to safely export additional cryptographic keys from secure channel protocols, modelled with the authenticated and confidential channel establishment (ACCE) security notion. For example, the EAP-TLS protocol uses the Transport Layer Security (TLS) handshake to output an additional shared secret which can be used for purposes outside of TLS, and the RFC 5705 standard specifies a general mechanism for exporting keying material from TLS. We show that, for a class of ACCE protocols we call TLS-like protocols, the EAP-TLS transformation can be used to export an additional key, and that the result is a secure AKE protocol in the BellareRogaway model. Interestingly, we are able to carry out the proof without looking at the specifics of the TLS protocol itself (beyond the notion that it is TLS-like), but rather are able to use the ACCE property in a semi black-box way. To facilitate our modular proof, we develop a novel technique, notably an encryption-based key checking mechanism that is used by the security reduction. Our results imply that EAP-TLS using secure TLS 1.2 cipher-suites is a secure authenticated key exchange protocol.
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