Cryptology ePrint Archive: Report 2009/588

Confidential Signatures and Deterministic Signcryption

Alexander W. Dent, Marc Fischlin, Mark Manulis, Martijn Stam and Dominique Schroder

Abstract: Encrypt-and-sign, where one encrypts and signs a message in parallel, is usually not recommended for confidential message transmission. The reason is that the signature typically leaks information about the message. This motivates our investigation of confidential signature schemes, which hide all information about (high-entropy) input messages. In this work we provide a formal treatment of confidentiality for such schemes and a comprehensive discussion of the relationship of different notions we propose. We give constructions meeting our notions, both in the random oracle model and the standard model. As part of this we show that full domain hash signatures achieve a weaker level of confidentiality than Fiat-Shamir signatures. We then revisit the connection of confidential signatures to signcryption schemes. We give formal security models for deterministic signcryption schemes for high-entropy and low-entropy messages, and prove encrypt-and-sign to be secure for confidential signature schemes and high-entropy messages. Finally, we show that one can derandomize any signcryption scheme in our model and obtain a secure deterministic scheme.

Category / Keywords: public-key cryptography / Digital signature, Signcryption, Deterministic

Date: received 1 Dec 2009

Contact author: a dent at rhul ac uk

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

Version: 20091204:080722 (All versions of this report)

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