IACR News item: 06 December 2013
Benjamin Dowling, Florian Giesen, Florian Kohlar, Jörg Schwenk, Douglas Stebila
ePrint ReportWe investigate the security of multi-ciphersuite protocols with re-used long-term keys. We show how to \"open\" the ACCE definition slightly so that, after each ciphersuites has been proven secure individually, they can then be used together in a secure multi-ciphersuite protocol, even when long-term keys are re-used across ciphersuites, provided the ciphersuites\' messages satisfy an independence property. We apply our definitions and composition theorem to the SSH protocol, showing that signed Diffie--Hellman SSH ciphersuites are individually ACCE-secure; they also satisfy the preconditions of our composition theorem, and thus SSH is multi-ciphersuite-secure even with re-use of long-term keys.
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