Abstract. In this paper, we improve the recent rebound and start-fromthe-middle attacks on AES-like permutations. Our new cryptanalysis technique uses the fact that one can view two rounds of such permutations as a layer of big Sboxes preceded and followed by simple affine transformations. The big Sboxes encountered in this alternative representation are named Super-Sboxes. We apply this method to two second-round SHA-3 candidates Grøstl and ECHO, and obtain improvements over the previous cryptanalysis results for these two schemes. Moreover, we improve the best distinguisher for the AES block cipher in the known-key setting, reaching 8 rounds for the 128-bit version.

Much research has focused on providing RFID tags with lightweight cryptographic functionality. The HB + authentication protocol was recently proposed [1] and claimed to be secure against both passive and active attacks. In this note we propose a linear-time active attack against HB + .

The innovative HB + protocol of Juels and Weis [10] extends device authentication to low-cost RFID tags. However, despite the very simple on-tag computation there remain some practical problems with HB + and despite an elegant proof of security against some limited active attacks, there is a simple man-in-the-middle attack due to Gilbert et al. [8]. In this paper we consider improvements to HB + in terms of both security and practicality. We introduce a new protocol that we denote random-HB #. This proposal avoids many practical drawbacks of HB + , remains provably resistant to attacks in the model of Juels and Weis, and at the same time is provably resistant to a broader class of active attacks that includes the attack of [8]. We then describe an enhanced variant called HB # which offers practical advantages over HB + .

Abstract. The white box attack context as described in [1,2] is the common setting where cryptographic software is executed in an untrusted environment-i.e. an attacker has gained access to the implementation of cryptographic algorithms, and can observe or manipulate the dynamic execution of whole or part of the algorithms. In this paper, we present an efficient practical attack against the obfuscated AES implementation [1] proposed at SAC 2002 as a means to protect AES software operated in the white box context against key exposure. We explain in details how to extract the whole AES secret key embedded in such a white box AES implementation, with negligible memory and worst time complexity 2 30 .

Sosemanuk is a new synchronous software-oriented stream cipher, corresponding to Profile 1 of the ECRYPT call for stream cipher primitives. Its key length is variable between 128 and 256 bits. It accommodates a 128-bit initial value. Any key length is claimed to achieve 128-bit security. The Sosemanuk cipher uses both some basic design principles from the stream cipher SNOW 2.0 and some transformations derived from the block cipher SERPENT. Sosemanuk aims at improving SNOW 2.0 both from the security and from the efficiency points of view. Most notably, it uses a faster IV-setup procedure. It also requires a reduced amount of static data, yielding better performance on several architectures.