IACR News item: 24 October 2013
Ivan Damgaard, Sebastian Faust, Pratyay Mukherjee, Daniele Venturi
ePrint Report1) We show that standard ID and signature schemes constructed from a large class of $\\Sigma$-protocols (including the Okamoto scheme, for instance) are secure even if the adversary can arbitrarily tamper with the prover\'s state a bounded number of times and obtain some bounded amount of leakage. Interestingly, for the Okamoto scheme we can allow also independent tampering with the public parameters.
2) We show a bounded tamper and leakage resilient CCA secure public key cryptosystem based on the DDH assumption. We first define a weaker CPA-like security notion that we can instantiate based on DDH, and then we give a general compiler that yields CCA-security with tamper and leakage resilience. This requires a public tamper-proof common reference string.
3) Finally, we explain how to boost bounded tampering and leakage resilience (as in 1. and 2. above) to continuous tampering and leakage resilience, in the so-called floppy model where each user has a personal hardware token (containing leak- and tamper-free information) which can be used to refresh the secret key.
We believe that bounded tampering is a meaningful and interesting alternative to avoid known impossibility results and can provide important insights into the security of existing standard cryptographic schemes.
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