This paper introduces a new adaptive chosen ciphertext attack against certain protocols based on RSA. We show that an RSA private-key operation can be performed if the attacker has access to an oracle that, for any chosen ciphertext, returns only one bit telling whether the ciphertext corresponds to some unknown block of data encrypted using PKCS #1. An example of a protocol susceptible to our attackisSSL V.3.0.

Previously, we developed a type system to ensure secure information flow in a sequential, imperative programming language [VSI96]. Program variables are classified as either high or low security; intuitively, we wish to prevent information from flowing from high variables to low variables. Here, we extend the analysis to deal with a multithreaded language. We show that the previous type system is insufficient to ensure a desirable security property called noninterference. Noninterference basically means that the final values of low variables are independent of the initial values of high variables. By modifying the sequential type system, we are able to guarantee noninterference for concurrent programs. Crucial to this result, however, is the use of purely nondeterministic thread scheduling. Since implementing such scheduling is problematic, we also show how a more restrictive type system can guarantee noninterference, given a more deterministic (and easily implementable) scheduling policy, such as round-robin time slicing. Finally, we consider the consequences of adding a clock to the language.

Differential Power Analysis, first introduced by Kocher et al. in [14], is a powerful technique allowing to recover secret smart card information by monitoring power signals. In [14] a specific DPA attack against smart-cards running the DES algorithm was described. As few as 1000 encryptions were sufficient to recover the secret key. In this paper we generalize DPA attack to elliptic curve (EC) cryptosystems and describe a DPA on EC Diffie-Hellman key exchange and EC El-Gamal type encryption. Those attacks enable to recover the private key stored inside the smart-card. Moreover, we suggest countermeasures that thwart our attack.

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In [15], we give a type system that guarantees that well-typed multi-threaded programs are possibilistically noninterfering. If thread scheduling is probabilistic, however, then well-typed programs may have probabilistic timing channels. We describe how they can be eliminated without making the type system more restrictive. We show that well-typed concurrent programs are probabilistically noninterfering if every total command with a high guard executes atomically. The proof uses the concept of a probabilistic state of a computation, following the work of Kozen [10].

Twofish is a 128-bit block cipher that accepts a variable-length key up to 256 bits. The cipher is a 16-round Feistel network with a bijective F function made up of four key-dependent 8-by-8-bit S-boxes, a fixed 4-by-4 maximum distance separable matrix over GF(2 8 ), a pseudo-Hadamard transform, bitwise rotations, and a carefully designed key schedule. A fully optimized implementation of Twofish encrypts on a Pentium Pro at 17.8 clock cycles per byte, and an 8-bit smart card implementation encrypts at 1660 clock cycles per byte. Twofish can be implemented in hardware in 14000 gates. The design of both the round function and the key schedule permits a wide variety of tradeoffs between speed, software size, key setup time, gate count, and memory. We have extensively cryptanalyzed Twofish; our best attack breaks 5 rounds with 2 22.5 chosen plaintexts and 2 51 effort.

Systems that authenticate a user based on a shared secret (such as a password or PIN) normally allow anyone to query whether the secret is a given value. For example, an ATM machine allows one to ask whether a string is the secret PIN of a (lost or stolen) ATM card. Yet such queries are prohibited in any model whose programs satisfy an informationflow property like Noninterference. But there is complexitybased justification for allowing these queries. A type system is given that provides the access control needed to prove that no well-typed program can leak secrets in polynomial time, or even leak them with nonnegligible probability if secrets are of sufficient length and randomly chosen. However, there are well-typed deterministic programs in a synchronous concurrent model capable of leaking secrets in linear time. 1

We present a model for attacking various cryptographic schemes by taking advantage of random hardware faults. The model consists of a black-box containing some cryptographic secret. The box interacts with the outside world by following a cryptographic protocol. The model supposes that from time to time the box is aected by a random hardware fault causing it to output incorrect values. For example, the hardware fault ips an internal register bit at some point during the computation. We show that for many digital signature and identication schemes these incorrect outputs completely expose the secrets stored in the box. We present the following results: (1) The secret signing key used in an implementation of RSA based on the Chinese Remainder Theorem (CRT) is completely exposed from a single erroneous RSA signature, (2) for non-CRT implementations of RSA the secret key is exposed given a large number (e.g. 1000) of erroneous signatures, (3) the secret key used in Fiat-Shamir ...

Abstract. This paper introduces simple methods to convert a cryptographic algorithm into an algorithm protected against simple sidechannel attacks. Contrary to previously known solutions, the proposed techniques are not at the expense of the execution time. Moreover, they are generic and apply to virtually any algorithm. In particular, we present several novel exponentiation algorithms, namely a protected square-and-multiply algorithm, its right-to-left counterpart, and several protected sliding-window algorithms. We also illustrate our methodology applied to point multiplication on elliptic curves. All these algorithms share the common feature that the complexity is globally unchanged compared to the corresponding unprotected implementations.

NIST has considered the performance of AES candidates on smart-cards as an important selection criterion and many submitters have highlighted the compactness and efficiency of their submission on low end smart cards. However, in light of recently discovered power based attacks, we strongly argue that evaluating smart-card suitability of AES candidates requires a very cautious approach. We demonstrate that straightforward implementations of AES candidates on smart cards, are highly vulnerable to power analysis and readily leak away all secret keys. To illustrate our point, we describe a power based attack on the Twofish Reference 6805 code which we implemented on a ST16 smart card. The attack required power samples from only 100 independent block encryptions to fully recover the 128-bit secret key. We also describe how all other AES candidates are susceptible to similar attacks. We review the basis of power attacks and suggest countermeasures for a secure implementation. Unfortun...