Cryptology ePrint Archive: Report 2003/214

Multi-Trapdoor Commitments and their Applications to Non-Malleable Protocols

Rosario Gennaro

Abstract: We introduce the notion of multi-trapdoor commitments which is a stronger form of trapdoor commitment schemes. We then construct two very efficient instantiations of multi-trapdoor commitment schemes, based on the Strong RSA Assumption and the recently introduced Strong Diffie-Hellman Assumption.

The main applications of our result are non-malleable trapdoor commtiments and a compiler} that takes any proof of knowledge and transforms it into one which is secure against a concurrent man-in-the-middle attack. Such a proof of knowledge immediately yields concurrently secure identification protocols.

When using our number-theoretic istantiations, the non-malleable commitment and the compiler are very efficient (require no more than four exponentiations). The latter also maintains the round complexity of the original proof of knowledge; it works in the common reference string model, which in any case is necessary to prove security of proofs of knowledge under this kind of attacks. Compared to previously known efficient solutions, ours is a factor of two faster.

Category / Keywords: cryptographic protocols / zero-knowledge, concurrency, authentication

Publication Info: Preliminary version in Crypto 2004

Date: received 7 Oct 2003, last revised 26 Nov 2004

Contact author: rosario at watson ibm com

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | BibTeX Citation

Version: 20041126:223434 (All versions of this report)

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