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Efficient modular exponentiation-based puzzles for denial-of-service protection

By Jothi Rangasamy, Douglas Stebila, Lakshmi Kuppusamy, Colin Boyd and Juan M. Gonzalez Nieto


Client puzzles are moderately-hard cryptographic problems neither easy nor impossible to solve that can be used as a counter-measure against denial of service attacks on network protocols. Puzzles based on modular exponentiation are attractive as they provide important properties such as non-parallelisability, deterministic solving time, and linear granularity. We propose an efficient client puzzle based on modular exponentiation. Our puzzle requires only a few modular multiplications for puzzle generation and verification. For a server under denial of service attack, this is a significant improvement as the best known non-parallelisable puzzle proposed by Karame and Capkun (ESORICS 2010) requires at least 2k-bit modular exponentiation, where k is a security parameter. We show that our puzzle satisfies the unforgeability and difficulty properties defined by Chen et al. (Asiacrypt 2009). We present experimental results which show that, for 1024-bit moduli, our proposed puzzle can be up to 30 times faster to verify than the Karame-Capkun puzzle and 99 times faster than the Rivest et al.'s time-lock puzzle

Topics: 080303 Computer System Security, client puzzles, RSA, time-lock puzzles, denial of service resistance, puzzle difficulty
Publisher: Springer
Year: 2012
DOI identifier: 10.1007/978-3-642-31912-9_21
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