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89
Appendonly signatures
 in International Colloquium on Automata, Languages and Programming
, 2005
"... Abstract. The strongest standard security notion for digital signature schemes is unforgeability under chosen message attacks. In practice, however, this notion can be insufficient due to “sidechannel attacks ” which exploit leakage of information about the secret internal state. In this work we pu ..."
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Cited by 53 (10 self)
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Abstract. The strongest standard security notion for digital signature schemes is unforgeability under chosen message attacks. In practice, however, this notion can be insufficient due to “sidechannel attacks ” which exploit leakage of information about the secret internal state. In this work we put forward the notion of “leakageresilient signatures, ” which strengthens the standard security notion by giving the adversary the additional power to learn a bounded amount of arbitrary information about the secret state that was accessed during every signature generation. This notion naturally implies security against all sidechannel attacks as long as the amount of information leaked on each invocation is bounded and “only computation leaks information.” The main result of this paper is a construction which gives a (treebased, stateful) leakageresilient signature scheme based on any 3time signature scheme. The amount of information that our scheme can safely leak per signature generation is 1/3 of the information the underlying 3time signature scheme can leak in total. Signature schemes that remain secure even if a bounded total amount of information is leaked were recently constructed, hence instantiating our construction with these schemes gives the first constructions of provably secure leakageresilient signature schemes. The above construction assumes that the signing algorithm can sample truly random bits, and thus an implementation would need some special hardware (randomness gates). Simply generating this randomness using a leakageresilient streamcipher will in general not work. Our second contribution is a sound general principle to replace uniform random bits in any leakageresilient construction with pseudorandom ones: run two leakageresilient streamciphers (with independent keys) in parallel and then apply a twosource extractor to their outputs. 1
Signature schemes with bounded leakage resilience
 In ASIACRYPT
, 2009
"... A leakageresilient cryptosystem remains secure even if arbitrary, but bounded, information about the secret key (or possibly other internal state information) is leaked to an adversary. Denote the length of the secret key by n. We show a signature scheme tolerating (optimal) leakage of up to n − nǫ ..."
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Cited by 41 (1 self)
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A leakageresilient cryptosystem remains secure even if arbitrary, but bounded, information about the secret key (or possibly other internal state information) is leaked to an adversary. Denote the length of the secret key by n. We show a signature scheme tolerating (optimal) leakage of up to n − nǫ bits of information about the secret key, and a more efficient onetime signature scheme that tolerates leakage of ( 1 4 −ǫ) ·n bits of information about the signer’s entire state. The latter construction extends to give a leakageresilient ttime signature scheme. All these constructions are in the standard model under general assumptions. 1
More constructions of lossy and correlationsecure trapdoor functions. Cryptology ePrint Archive, Report 2009/590
, 2009
"... We propose new and improved instantiations of lossy trapdoor functions (Peikert and Waters, STOC ’08), and correlationsecure trapdoor functions (Rosen and Segev, TCC ’09). Our constructions widen the set of numbertheoretic assumptions upon which these primitives can be based, and are summarized as ..."
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Cited by 38 (8 self)
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We propose new and improved instantiations of lossy trapdoor functions (Peikert and Waters, STOC ’08), and correlationsecure trapdoor functions (Rosen and Segev, TCC ’09). Our constructions widen the set of numbertheoretic assumptions upon which these primitives can be based, and are summarized as follows: • Lossy trapdoor functions based on the quadratic residuosity assumption. Our construction relies on modular squaring, and whereas previous such constructions were based on seemingly stronger assumptions, we present the first construction that is based solely on the quadratic residuosity assumption. We also present a generalization to higher order power residues. • Lossy trapdoor functions based on the composite residuosity assumption. Our construction guarantees essentially any required amount of lossiness, where at the same time the functions are more efficient than the matrixbased approach of Peikert and Waters. • Lossy trapdoor functions based on the dLinear assumption. Our construction both simplifies the DDHbased construction of Peikert and Waters, and admits a generalization to the whole family of dLinear assumptions without any loss of efficiency. • Correlationsecure trapdoor functions related to the hardness of syndrome decoding. Keywords: Publickey encryption, lossy trapdoor functions, correlationsecure trapdoor functions. An extended abstract of this work appears in Public Key Cryptography — PKC 2010, Springer LNCS 6056
Circular and leakage resilient publickey encryption under subgroup indistinguishability  (or: Quadratic residuosity strikes back
 In CRYPTO
, 2010
"... The main results of this work are new publickey encryption schemes that, under the quadratic residuosity (QR) assumption (or Paillier’s decisional composite residuosity (DCR) assumption), achieve keydependent message security as well as high resilience to secret key leakage and high resilience to ..."
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Cited by 33 (4 self)
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The main results of this work are new publickey encryption schemes that, under the quadratic residuosity (QR) assumption (or Paillier’s decisional composite residuosity (DCR) assumption), achieve keydependent message security as well as high resilience to secret key leakage and high resilience to the presence of auxiliary input information. In particular, under what we call the subgroup indistinguishability assumption, of which the QR and DCR are special cases, we can construct a scheme that has: • Keydependent message (circular) security. Achieves security even when encrypting affine functions of its own secret key (in fact, w.r.t. affine “keycycles ” of predefined length). Our scheme also meets the requirements for extending keydependent message security to broader classes of functions beyond affine functions using previous techniques of [BGK, ePrint09] or [BHHI, Eurocrypt10]. • Leakage resiliency. Remains secure even if any adversarial lowentropy (efficiently computable) function of the secret key is given to the adversary. A proper selection of parameters allows for a “leakage rate ” of (1 − o(1)) of the length of the secret key.
Vulnerability bounds and leakage resilience of blinded cryptography under timing attacks
 in 2010 IEEE Computer Security Foundations
, 2010
"... Abstract—We establish formal bounds for the number of minentropy bits that can be extracted in a timing attack against a cryptosystem that is protected by blinding, the stateofthe art countermeasure against timing attacks. Compared with existing bounds, our bounds are both tighter and of greater ..."
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Cited by 30 (7 self)
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Abstract—We establish formal bounds for the number of minentropy bits that can be extracted in a timing attack against a cryptosystem that is protected by blinding, the stateofthe art countermeasure against timing attacks. Compared with existing bounds, our bounds are both tighter and of greater operational significance, in that they directly address the key’s oneguess vulnerability. Moreover, we show that any semantically secure publickey cryptosystem remains semantically secure in the presence of timing attacks, if the implementation is protected by blinding and bucketing. This result shows that, by considering (and justifying) more optimistic models of leakage than recent proposals for leakageresilient cryptosystems, one can achieve provable resistance against sidechannel attacks for standard cryptographic primitives. I.
Achieving leakage resilience through dual system encryption
 In TCC
, 2011
"... In this work, we show that strong leakage resilience for cryptosystems with advanced functionalities can be obtained quite naturally within the methodology of dual system encryption, recently introduced by Waters. We demonstrate this concretely by providing fully secure IBE, HIBE, and ABE systems wh ..."
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Cited by 28 (5 self)
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In this work, we show that strong leakage resilience for cryptosystems with advanced functionalities can be obtained quite naturally within the methodology of dual system encryption, recently introduced by Waters. We demonstrate this concretely by providing fully secure IBE, HIBE, and ABE systems which are resilient to bounded leakage from each of many secret keys per user, as well as many master keys. This can be realized as resilience against continual leakage if we assume keys are periodically updated and no (or logarithmic) leakage is allowed during the update process. Our systems are obtained by applying a simple modification to previous dual system encryption constructions: essentially this provides a generic tool for making dual system encryption schemes leakageresilient. 1
Afterthefact leakage in publickey encryption
 TCC 2011, volume 6597 of LNCS
, 2011
"... What does it mean for an encryption scheme to be leakageresilient? Prior formulations require that the scheme remains semantically secure even in the presence of leakage, but only considered leakage that occurs before the challenge ciphertext is generated. Although seemingly necessary, this restric ..."
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Cited by 24 (0 self)
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What does it mean for an encryption scheme to be leakageresilient? Prior formulations require that the scheme remains semantically secure even in the presence of leakage, but only considered leakage that occurs before the challenge ciphertext is generated. Although seemingly necessary, this restriction severely limits the usefulness of the resulting notion. In this work we study afterthefact leakage, namely leakage that the adversary obtains after seeing the challenge ciphertext. We seek a “natural ” and realizable notion of security, which is usable in higherlevel protocols and applications. To this end, we formulate entropic leakageresilient PKE. This notion captures the intuition that as long as the entropy of the encrypted message is higher than the amount of leakage, the message still has some (pseudo) entropy left. We show that this notion is realized by the NaorSegev constructions (using hash proof systems). We demonstrate that entropic leakageresilience is useful by showing a simple construction that uses it to get semantic security in the presence of afterthefact leakage, in a model of bounded memory leakage from a split state. 1
Fully LeakageResilient Signatures
, 2010
"... A signature scheme is fully leakage resilient (Katz and Vaikuntanathan, ASIACRYPT ’09) if it is existentially unforgeable under an adaptive chosenmessage attack even in a setting where an adversary may obtain bounded (yet arbitrary) leakage information on all intermediate values that are used throu ..."
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Cited by 23 (3 self)
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A signature scheme is fully leakage resilient (Katz and Vaikuntanathan, ASIACRYPT ’09) if it is existentially unforgeable under an adaptive chosenmessage attack even in a setting where an adversary may obtain bounded (yet arbitrary) leakage information on all intermediate values that are used throughout the lifetime of the system. This is a strong and meaningful notion of security that captures a wide range of sidechannel attacks. One of the main challenges in constructing fully leakageresilient signature schemes is dealing with leakage that may depend on the random bits used by the signing algorithm, and constructions of such schemes are known only in the randomoracle model. Moreover, even in the randomoracle model, known schemes are only resilient to leakage of less than half the length of their signing key. In this paper we construct the first fully leakageresilient signature schemes without random oracles. We present a scheme that is resilient to any leakage of length (1 − o(1))L bits, where L is the length of the signing key. Our approach relies on generic cryptographic primitives, and at the same time admits rather efficient instantiations based on specific numbertheoretic
Reconstructing rsa private keys from random key bits
 In CRYPTO
, 2009
"... We show that an RSA private key with small public exponent can be efficiently recovered given a 0.27 fraction of its bits at random. An important application of this work is to the “cold boot ” attacks of Halderman et al. We make new observations about the structure of RSA keys that allow our algori ..."
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Cited by 22 (1 self)
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We show that an RSA private key with small public exponent can be efficiently recovered given a 0.27 fraction of its bits at random. An important application of this work is to the “cold boot ” attacks of Halderman et al. We make new observations about the structure of RSA keys that allow our algorithm to make use of the redundant information in the typical storage format of an RSA private key. Our algorithm itself is elementary and does not make use of the lattice techniques used in other RSA key reconstruction problems. We give an analysis of the running time behavior of our algorithm that matches the threshold phenomenon observed in our experiments. 1
Securing computation against continuous leakage
 In CRYPTO
, 2010
"... Abstract. We present a general method to compile any cryptographic algorithm into one which resists side channel attacks of the only computation leaks information variety for an unbounded number of executions. Our method uses as a building block a semantically secure subsidiary bit encryption scheme ..."
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Cited by 22 (2 self)
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Abstract. We present a general method to compile any cryptographic algorithm into one which resists side channel attacks of the only computation leaks information variety for an unbounded number of executions. Our method uses as a building block a semantically secure subsidiary bit encryption scheme with the following additional operations: key refreshing, oblivious generation of cipher texts, leakage resilience regeneration, and blinded homomorphic evaluation of one single complete gate (e.g. NAND). Furthermore, the security properties of the subsidiary encryption scheme should withstand bounded leakage incurred while performing each of the above operations. We show how to implement such a subsidiary encryption scheme under the DDH intractability assumption and the existence of a simple secure hardware component. The hardware component is independent of the encryption scheme secret key. The subsidiary encryption scheme resists leakage attacks where the leakage is computable in polynomial time and of length bounded by a constant fraction of the security parameter. 1