Cryptology ePrint Archive: Report 2003/067

Forking Lemmas in the Ring Signatures' Scenario

Javier Herranz and Germán Sáez

Abstract: Pointcheval and Stern introduced in 1996 some forking lemmas useful to prove the security of a family of digital signature schemes. This family includes, for example, Schnorr's scheme and a modification of ElGamal signature scheme.

In this work we generalize these forking lemmas to the ring signatures' scenario. In a ring signature scheme, a signer in a subset (or {\it ring}) of potential signers produces a signature of a message in such a way that the receiver can verify that the signature comes from a member of the ring, but cannot know which member has actually signed.

We propose a new ring signature scheme, based on Schnorr signature scheme, which provides unconditional anonymity. We use the generalized forking lemmas to prove that this scheme is existentially unforgeable under adaptive chosen-message attacks, in the random oracle model.

Category / Keywords: public-key cryptography / ring signature schemes, unforgeability against chosen-message attacks, random oracle model

Date: received 10 Apr 2003

Contact author: jherranz at mat upc es

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Version: 20030411:175017 (All versions of this report)

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