Abstract. Key derivation refers to the process by which an agreed upon large random number, often named master secret, is used to derive keys to encrypt and authenticate data. Practitioners and standardization bodies have usually used the random oracle model to get key material from a Diffie-Hellman key exchange. However, formal proofs in the standard model require randomness extractors to formally extract the entropy of the random master secret into a seed prior to derive other keys. Whereas this is a quite simple tool, it is not easy to use in practice —or it is easy to misuse it—. In addition, in many standards, the acronym PRF (Pseudo-Random Functions) is used for several tasks, and namely the randomness extraction. While randomness extractors and pseudo-random functions are a priori distinct tools, we first study whether such an application is correct or not. We thereafter study DH-key exchange, in the cases of prime subgroups of Z ⋆ p (and namely where p is a safe-prime) and of elliptic curves, since in IPSec, for example, only these groups are considered. We present very efficient and provable randomness extraction techniques for these groups under the DDH assumption. In the special case of elliptic curves, we present a new technique —the so-called ’Twist-AUgmented’ technique — an alternative to randomness extractors which exploits specific properties of some elliptic curves. We finally compare the efficiency of this method with other solutions.

Key derivation refers to the process by which an agreed upon large random number, often named master secret, is used to derive keys to encrypt and authenticate data. Practitioners and standardization bodies have usually used the random oracle model to get key material from a Di#e-Hellman key exchange. However, proofs in the standard model require randomness extractors to formally extract the entropy of the random master secret into a seed prior to derive other keys.

Abstract— During designing of cryptographic protocols, their participants are usually identified with software or hardware they use. However, these supporting tools are not verified at the protocol level. Such carelessness opens the door to kleptographic (SETUP) attacks. In this paper we design such an attack on the classical Benaloh-Tuinstra election protocol. One of the technical tools developed in the paper is a new variant of a Diffie-Hellman SETUP attack, in which Kronecker Decomposition of the group is not known to the attacker. This is especially the case of Goldwasser-Micali cryptosystem. I.

In this paper, we present a new fault attack on elliptic curve scalar product algorithms. This attack is tailored to work on the classical Montgomery ladder method when the y-coordinate is not used. No weakness has been reported so far on such implementations, which are very efficient and were promoted by several authors. But taking into account the twist of the elliptic curves, we show how, with few faults (around one or two faults), we can retrieve the full secret exponent even if classical countermeasures are employed to prevent fault attacks. It turns out that this attack has not been anticipated as the security of the elliptic curve parameters in most standards can be strongly reduced. Especially, the attack is meaningful on some NIST or SECG parameters.

Abstract. We discuss a recently proposed formal proof model for RFID location privacy. We show that protocols which intuitively and in several other models are considered not to be location private, are provably location private in this model. Conversely, we also show that protocols which obviously are location private, are not considered location private in this model. Specifically, we prove a protocol in which every tag transmits the same constant message to not be location private in the proposed model. Then we prove a protocol in which a tag’s identity is transmitted in clear text to be weakly location private in the model. Finally, we consider a protocol with known weaknesses with respect to location privacy and show it to be location private in the model.