Cryptology ePrint Archive: Report 2014/500

Verifiable and Secure Outsourcing Schemes of Modular Exponentiations Using One Untrusted Cloud Server and Their Application

Can Xiang and Chunming Tang

Abstract: Modular exponentiation is one of basic operations among most of current cryptosystems. Under some algebraic assumptions or cryptography assumptions, it can construct outsourcing schemes for modular exponentiations by using two untrusted cloud servers, which cannot resist the collusive attack of two untrusted cloud servers. However, it doesn't exist an efficient outsourcing of modular exponentiations using one untrusted cloud server. In this paper, we present three secure outsourcing schemes using one untrusted cloud server, which can enable user to securely outsource exponentiations to single cloud server. The first one is a secure outsourcing scheme for fixed base-variable exponent modular exponentiations, the second is for variable base-variable exponent modular exponentiations, and the third is a secure outsourcing scheme for simultaneous modular exponentiations. Compared with other proposed schemes, our proposed schemes are superior in both efficiency and checkability. Moreover, our schemes are secure without any cryptographic assumptions. Finally, we give two applications for our outsourcing schemes, one is to construct an outsourcing scheme for Cramer-Shoup encryptions, and the other is to design an outsourcing scheme for Schnorr signatures.

Category / Keywords: applications /

Date: received 25 Jun 2014, withdrawn 7 Mar 2015

Contact author: xiangcan1987 at sina com

Available format(s): (-- withdrawn --)

Version: 20150307:220843 (All versions of this report)

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