Research -- Vishal Saraswat

Anonymous Signatures Revisited

with Dr. Aaram Yun. In J. Pieprzyk and F. Zhang (Eds.): ProvSec 2009, LNCS vol. 5848, pp. 140-153, Springer-Verlag, 2009. Updated version available at Cryptology ePrint Archive: Report 2009/307.

Abstract: We revisit the notion of the anonymous signature, first formalized by Yang, Wong, Deng and Wang [11], and then further developed by Fischlin [5] and Zhang and Imai [12]. We present a new formalism of anonymous signature, where instead of the message, a part of the signature is withheld to maintain anonymity. We introduce the notion unpretendability to guarantee infeasibility for someone other than the correct signer to pretend authorship of the message and signature. Our definition retains applicability for all previous applications of the anonymous signature, provides stronger security, and is conceptually simpler. We give a generic construction from any ordinary signature scheme, and also show that the short signature scheme by Boneh and Boyen [2] can be naturally regarded as such a secure anonymous signature scheme according to our formalism.

Public-Key Encryption with Searchable Keywords based on Jacobi Symbols

with Dr. Giovanni Di Crescenzo. In K. Srinathan, C. Pandu Rangan, and Moti Yung, (Eds.): IndoCrypt 2007, LNCS vol. 4859, pp. 282-296, Springer-Verlag, 2007

Abstract: Public-key encryption schemes with searchable keywords are useful to delegate searching capabilities on encrypted data to a third party, who does not hold the entire secret key, but only an appropriate token which allows searching operations but preserves data privacy. Such notion was previously proved to imply identity-based public-key encryption [5] and to be equivalent to anonymous (or key-private) identity-based encryption which are useful for fully-private communication. So far all presented public-key encryption with keyword search (PEKS) schemes were based on bilinear forms and finding a PEKS that is not based on bilinear forms has been an open problem since the notion of PEKS was first introduced in [5]. We construct a public-key encryption scheme with keyword search based on a variant of the quadratic residuosity problem. We obtain our scheme using a non-trivial transformation of Cocks' identity-based encryption scheme [9]. Thus we show that the primitive of PEKS can be based on additional intractability assumptions which is a conventional desiderata about all cryptographic primitives.

Here is the proof for the equivalence of the Quadratic Indistinguishability Problem and the Quadratic Residuosity Problem.

Secure and Efficient Long Term Data Management, Intelligent Storage Consortium, Digital Technology Center (DTC), UMN, Jun 2007 - May 2008

Long Term Key Management, Intelligent Storage Consortium, DTC, UMN, Jun 2007 - May 2008

Applied Remote Cache-timing Attacks Against AES, Institute of Technology, UMN, Sept 2006 - Apr 2007

A Note on Cryptographic Multilinear Maps, Institute of Technology, UMN, Twin Cities, May 2005

Basic Lie Theory, School of Mathematics, Tata Institute of Fundamental Research (TIFR), Bombay, July 2003