Cryptology ePrint Archive: Report 2012/154

The Joint Signature and Encryption Revisited

Laila El Aimani

Abstract: We study the Sign_then_Encrypt, Commit_then_Encrypt_and_Sign, and Encrypt_then_Sign paradigms in the context of two cryptographic primitives, namely designated confirmer signatures and signcryption. Our study identifies weaknesses in those paradigms which impose the use of expensive encryption (as a building block) in order to meet a reasonable security level. Next, we propose some optimizations which annihilate the found weaknesses and allow consequently cheap encryption without compromising the overall security. Our optimizations further enjoy verifiability, a property profoundly needed in many real-life applications of the studied primitives.

Category / Keywords: public-key cryptography/ Sign_then_Encrypt, Commit_then_Encrypt_and_Sign, Encrypt_then_Sign, (public) verifiability, designated confirmer signatures, signcryption, zero knowledge proofs.

Date: received 23 Mar 2012, last revised 31 Oct 2016, withdrawn 14 Jun 2017

Contact author: laila elaimani at yahoo fr

Available format(s): (-- withdrawn --)

Version: 20170614:171529 (All versions of this report)

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