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Leakageresilient cryptography
 In Proceedings of the 49th IEEE Symposium on Foundation of Computer Science
, 2008
"... We construct a streamcipher S whose implementation is secure even if a bounded amount of arbitrary (adversarially chosen) information on the internal state of S is leaked during computation. This captures all possible sidechannel attacks on S where the amount of information leaked in a given peri ..."
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Cited by 143 (9 self)
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We construct a streamcipher S whose implementation is secure even if a bounded amount of arbitrary (adversarially chosen) information on the internal state of S is leaked during computation. This captures all possible sidechannel attacks on S where the amount of information leaked in a given period is bounded, but overall can be arbitrary large. The only other assumption we make on the implementation of S is that only data that is accessed during computation leaks information. The streamcipher S generates its output in chunks K1,K2,..., and arbitrary but bounded information leakage is modeled by allowing the adversary to adaptively chose a function fℓ: {0, 1} ∗ → {0, 1}λ before Kℓ is computed, she then gets fℓ(τℓ) where τℓ is the internal state of S that is accessed during the computation of Kℓ. One notion of security we prove for S is that Kℓ is indistinguishable from random when given K1,...,Kℓ−1, f1(τ1),..., fℓ−1(τℓ−1) and also the complete internal state of S after Kℓ has been computed (i.e. S is forwardsecure). The construction is based on alternating extraction (used in the intrusionresilient secretsharing scheme from FOCS’07). We move this concept to the computational setting by proving a lemma that states that the output of any PRG has high HILL pseudoentropy (i.e. is indistinguishable from some distribution with high minentropy) even if arbitrary information about the seed is leaked. The amount of leakage λ that we can tolerate in each step depends on the strength of the underlying PRG, it is at least logarithmic, but can be as large as a constant fraction of the internal state of S if the PRG is exponentially hard. 1.
Simultaneous hardcore bits and cryptography against memory attacks
 IN TCC
, 2009
"... This paper considers two questions in cryptography. Cryptography Secure Against Memory Attacks. A particularly devastating sidechannel attack against cryptosystems, termed the “memory attack”, was proposed recently. In this attack, a significant fraction of the bits of a secret key of a cryptograp ..."
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Cited by 116 (11 self)
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This paper considers two questions in cryptography. Cryptography Secure Against Memory Attacks. A particularly devastating sidechannel attack against cryptosystems, termed the “memory attack”, was proposed recently. In this attack, a significant fraction of the bits of a secret key of a cryptographic algorithm can be measured by an adversary if the secret key is ever stored in a part of memory which can be accessed even after power has been turned off for a short amount of time. Such an attack has been shown to completely compromise the security of various cryptosystems in use, including the RSA cryptosystem and AES. We show that the publickey encryption scheme of Regev (STOC 2005), and the identitybased encryption scheme of Gentry, Peikert and Vaikuntanathan (STOC 2008) are remarkably robust against memory attacks where the adversary can measure a large fraction of the bits of the secretkey, or more generally, can compute an arbitrary function of the secretkey of bounded output length. This is done without increasing the size of the secretkey, and without introducing any
PublicKey Cryptosystems Resilient to Key Leakage
"... Most of the work in the analysis of cryptographic schemes is concentrated in abstract adversarial models that do not capture sidechannel attacks. Such attacks exploit various forms of unintended information leakage, which is inherent to almost all physical implementations. Inspired by recent sidec ..."
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Cited by 89 (6 self)
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Most of the work in the analysis of cryptographic schemes is concentrated in abstract adversarial models that do not capture sidechannel attacks. Such attacks exploit various forms of unintended information leakage, which is inherent to almost all physical implementations. Inspired by recent sidechannel attacks, especially the “cold boot attacks ” of Halderman et al. (USENIX Security ’08), Akavia, Goldwasser and Vaikuntanathan (TCC ’09) formalized a realistic framework for modeling the security of encryption schemes against a wide class of sidechannel attacks in which adversarially chosen functions of the secret key are leaked. In the setting of publickey encryption, Akavia et al. showed that Regev’s latticebased scheme (STOC ’05) is resilient to any leakage of
A leakageresilient mode of operation
 In EUROCRYPT
, 2009
"... Abstract. A weak pseudorandom function (wPRF) is a pseudorandom functions with a relaxed security requirement, where one only requires the output to be pseudorandom when queried on random (and not adversarially chosen) inputs. We show that unlike standard PRFs, wPRFs are secure against memory attack ..."
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Cited by 76 (5 self)
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Abstract. A weak pseudorandom function (wPRF) is a pseudorandom functions with a relaxed security requirement, where one only requires the output to be pseudorandom when queried on random (and not adversarially chosen) inputs. We show that unlike standard PRFs, wPRFs are secure against memory attacks, that is they remain secure even if a bounded amount of information about the secret key is leaked to the adversary. As an application of this result we propose a simple mode of operation which – when instantiated with any wPRF – gives a leakageresilient streamcipher. Such a cipher is secure against any sidechannel attack, as long as the amount of information leaked per round is bounded, but overall can be arbitrary large. This construction is simpler than the only previous one (DziembowskiPietrzak FOCS’08) as it only uses a single primitive (a wPRF) in a straight forward manner. 1
Onetime programs
 In Advances in Cryptology – CRYPTO ’08
, 2008
"... Abstract. In this work, we introduce onetime programs, a new computational paradigm geared towards security applications. A onetime program can be executed on a single input, whose value can be specified at run time. Other than the result of the computation on this input, nothing else about the pr ..."
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Cited by 54 (8 self)
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Abstract. In this work, we introduce onetime programs, a new computational paradigm geared towards security applications. A onetime program can be executed on a single input, whose value can be specified at run time. Other than the result of the computation on this input, nothing else about the program is leaked. Hence, a onetime program is like a black box function that may be evaluated once and then “self destructs. ” This also extends to ktime programs, which are like black box functions that can be evaluated k times and then self destruct. Onetime programs serve many of the same purposes of program obfuscation, the obvious one being software protection, but also including applications such as temporary transfer of cryptographic ability. Moreover, the applications of onetime programs go well beyond those of obfuscation, since onetime programs can only be executed once (or more generally, a limited number of times) while obfuscated programs have no such bounds. For example, onetime programs lead naturally to electronic
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
Efficient NonMalleable Codes and KeyDerivation for PolySize Tampering Circuits
, 2013
"... Nonmalleable codes, defined by Dziembowski, Pietrzak and Wichs (ICS ’10), provide roughly the following guarantee: if a codeword c encoding some message x is tampered to c ′ = f(c) such that c ′ = c, then the tampered message x ′ contained in c ′ reveals no information about x. Nonmalleable codes ..."
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Cited by 23 (7 self)
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Nonmalleable codes, defined by Dziembowski, Pietrzak and Wichs (ICS ’10), provide roughly the following guarantee: if a codeword c encoding some message x is tampered to c ′ = f(c) such that c ′ = c, then the tampered message x ′ contained in c ′ reveals no information about x. Nonmalleable codes have applications to immunizing cryptosystems against tampering attacks and relatedkey attacks. One cannot have an efficient nonmalleable code that protects against all efficient tampering functions f. However, in this work we show “the next best thing”: for any polynomial bound s given apriori, there is an efficient nonmalleable code that protects against all tampering functions f computable by a circuit of size s. More generally, for any family of tampering functions F of size F  ≤ 2s, there is an efficient nonmalleable code that protects against all f ∈ F. The rate of our codes, defined as the ratio of message to codeword size, approaches 1. Our results are informationtheoretic and our main proof technique relies on a careful probabilistic method argument using limited independence. As a result, we get an efficiently samplable family of efficient codes, such that a random member of the family is nonmalleable with overwhelming
Nonmalleable codes from twosource extractors. Unpublished manuscript
, 2013
"... Abstract. We construct an efficient informationtheoretically nonmalleable code in the splitstate model for onebit messages. Nonmalleable codes were introduced recently by Dziembowski, Pietrzak and Wichs (ICS 2010), as a general tool for storing messages securely on hardware that can be subject t ..."
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Cited by 19 (3 self)
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Abstract. We construct an efficient informationtheoretically nonmalleable code in the splitstate model for onebit messages. Nonmalleable codes were introduced recently by Dziembowski, Pietrzak and Wichs (ICS 2010), as a general tool for storing messages securely on hardware that can be subject to tampering attacks. Informally, a code (Enc: M → L×R, Dec: L × R → M) is nonmalleable in the splitstate model if any adversary, by manipulating independently L and R (where (L, R) is an encoding of some message M), cannot obtain an encoding of a message M ′ that is not equal to M but is “related ” M in some way. Until now it was unknown how to construct an informationtheoretically secure code with such a property, even for M = {0, 1}. Our construction solves this problem. Additionally, it is leakageresilient, and the amount of leakage that we can tolerate can be an arbitrary fraction ξ < 1/4 of the length of the codeword. Our code is based on the innerproduct twosource extractor, but in general it can be instantiated by any twosource extractor that has large output and has the property of being flexible, which is a new notion that we define. We also show that the nonmalleable codes for onebit messages have an equivalent, perhaps simpler characterization, namely such codes can be defined as follows: if M is chosen uniformly from {0, 1} then the probability (in the experiment described above) that the output message M ′ is not equal to M can be at most 1/2 + ɛ. 1
Nonmalleable Codes from Additive Combinatorics
, 2013
"... Nonmalleable codes provide a useful and meaningful security guarantee in situations where traditional errorcorrection (and even errordetection) is impossible; for example, when the attacker can completely overwrite the encoded message. Informally, a code is nonmalleable if the message contained ..."
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Cited by 18 (5 self)
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Nonmalleable codes provide a useful and meaningful security guarantee in situations where traditional errorcorrection (and even errordetection) is impossible; for example, when the attacker can completely overwrite the encoded message. Informally, a code is nonmalleable if the message contained in a modified codeword is either the original message, or a completely unrelated value. Although such codes do not exist if the family of “tampering functions ” F is completely unrestricted, they are known to exist for many broad tampering families F. One such natural family is the family of tampering functions in the so called splitstate model. Here the message m is encoded into two shares L and R, and the attacker is allowed to arbitrarily tamper with L and R individually. The splitstate tampering arises in many realistic applications, such as the design of nonmalleable secret sharing schemes, motivating the question of designing efficient nonmalleable codes in this model. Prior to this work, nonmalleable codes in the splitstate model received considerable attention in the literature, but were constructed either (1) in the random oracle model [14], or (2) relied on advanced cryptographic assumptions (such as noninteractive zeroknowledge proofs and leakageresilient
Tamper and Leakage Resilience in the SplitState Model
, 2011
"... It is notoriously difficult to create hardware that is immune from side channel and tampering attacks. A lot of recent literature, therefore, has instead considered algorithmic defenses from such attacks. In this paper, we show how to algorithmically secure any cryptographic functionality from conti ..."
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Cited by 18 (3 self)
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It is notoriously difficult to create hardware that is immune from side channel and tampering attacks. A lot of recent literature, therefore, has instead considered algorithmic defenses from such attacks. In this paper, we show how to algorithmically secure any cryptographic functionality from continual splitstate leakage and tampering attacks. A splitstate attack on cryptographic hardware is one that targets separate parts of the hardware separately. Our construction does not require the hardware to have access to randomness. On contrast, prior work on protecting from continual combined leakage and tampering [KKS11] required true randomness for each update. Our construction is in the common reference string (CRS) model; the CRS must be hardwired into the device. We note that prior negative results show that it is impossible to algorithmically secure a cryptographic functionality against a combination of arbitrary continual leakage and tampering attacks without true randomness; therefore restricting our attention to the splitstate model is justified. Our construction is simple and modular, and relies on a new construction, in the CRS model, of nonmalleable codes with respect to splitstate tampering functions, which may be of independent interest. 1