Cryptology ePrint Archive: Report 2003/240

How to Break and Repair a Universally Composable Signature Functionality

Michael Backes and Dennis Hofheinz

Abstract: Canetti and Rabin recently proposed a universally composable ideal functionality F_SIG for digital signatures. We show that this functionality cannot be securely realized by \emph{any} signature scheme, thereby disproving their result that any signature scheme that is existentially unforgeable under adaptive chosen-message attack is a secure realization.

Next, an improved signature functionality is presented. We show that our improved functionality can be securely realized by precisely those signature schemes that are secure against existential forgery under adaptive chosen-message attacks.

Category / Keywords: cryptographic protocols / digital signature schemes, universal composability, adaptive chosen-message attack

Date: received 19 Nov 2003, last revised 19 Nov 2003

Contact author: hofheinz at ira uka de

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Version: 20031119:213754 (All versions of this report)

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