Cryptology ePrint Archive: Report 2016/087
Safely Exporting Keys from Secure Channels: On the Security of EAP-TLS and TLS Key Exporters
Christina Brzuska and Håkon Jacobsen and Douglas Stebila
Abstract: We investigate how to safely export additional cryptographic keys from secure channel protocols, modeled 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 Bellare–Rogaway 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.
Category / Keywords: AKE, ACCE, provable security, EAP-TLS, key exporters
Original Publication (with minor differences): IACR-EUROCRYPT-2016
Date: received 1 Feb 2016, last revised 10 May 2016
Contact author: hakoja at item ntnu no
Available format(s): PDF | BibTeX Citation
Note: Increased figure sizes, fixed typos.
Version: 20160510:223540 (All versions of this report)
Short URL: ia.cr/2016/087
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