Leakage resilient ElGamal encryption Conference Paper

Author(s): Kiltz, Eike; Pietrzak, Krzysztof
Title: Leakage resilient ElGamal encryption
Title Series: LNCS
Abstract: Blinding is a popular and well-known countermeasure to protect public-key cryptosystems against side-channel attacks. The high level idea is to randomize an exponentiation in order to prevent multiple measurements of the same operation on different data, as such measurements might allow the adversary to learn the secret exponent. Several variants of blinding have been proposed in the literature, using additive or multiplicative secret-sharing to blind either the base or the exponent. These countermeasures usually aim at preventing particular side-channel attacks (mostly power analysis) and come without any formal security guarantee. In this work we investigate to which extend blinding can provide provable security against a general class of side-channel attacks. Surprisingly, it turns out that in the context of public-key encryption some blinding techniques are more suited than others. In particular, we consider a multiplicatively blinded version of ElGamal public-key encryption where - we prove that the scheme, instantiated over bilinear groups of prime order p (where p - 1 is not smooth) is leakage resilient in the generic-group model. Here we consider the model of chosen-ciphertext security in the presence of continuous leakage, i.e., the scheme remains chosen-ciphertext secure even if with every decryption query the adversary can learn a bounded amount (roughly log(p)/2 bits) of arbitrary, adversarially chosen information about the computation. - we conjecture that the scheme, instantiated over arbitrary groups of prime order p (where p - 1 is not smooth) is leakage resilient. Previous to this work no encryption scheme secure against continuous leakage was known. Constructing a scheme that can be proven secure in the standard model remains an interesting open problem.
Keywords: Provable security; Encryption schemes; General class; Side channel attack; The standard model; ElGamal; Blinding technique; Chosen ciphertext security; Ciphertexts; Decryption query; Elgamal encryption; Exponentiations; Formal security; Group models; Multiple measurements; Open problems; Power analysis; Prime orders; Public-key cryptosystems; Public-key encryption; Secret exponents
Conference Title: ASIACRYPT: Theory and Application of Cryptology and Information Security
Volume: 6477
Conference Dates: December 5-9, 2010
Conference Location: Singapore
ISBN: 978-3-642-17372-1
Publisher: Springer  
Date Published: 2010-01-14
Start Page: 595
End Page: 612
Copyright Statement: © 2010 International Association for Cryptologic Research.
DOI: 10.1007/978-3-642-17373-8_34
Open access: no
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