We consider the problem of designing distinguishers and nonrandomness detectors for stream ciphers using the maximum degree monomial test. We construct an improved algorithm to determine the subset of key and IV-bits used in the test. The algorithm is generic, and can be applied to any stream cipher. In addition to this, the algorithm is highly tweakable, and can be adapted depending on the des...

The stream ciphers Py, Pypy and Py6 were designed by Biham and Seberry for the ECRYPT-eSTREAM project in 2005. The ciphers were promoted to the ‘Focus’ ciphers of the Phase II of the eSTREAM project. However, due to some cryptanalytic results on the ciphers, strengthened versions of the ciphers, namely TPy, TPypy and TPy6 were built. So far there exists no attacks on TPy6. In this paper, we fin...

Algebraic attacks on stream ciphers [9] recover the key by solving an overdefined system of multivariate equations. Such attacks can break several interesting cases of LFSR-based stream ciphers, when the output is obtained by a Boolean function, see [9– 11]. Recently this approach has been successfully extended also to combiners with memory, provided the number of memory bits is small, see [1, ...

The Fibonacci-to-Galois transformation is useful for reducing the propagation delay of feedback shift register-based stream ciphers and hash functions. In this paper, we extend it to handle Galois-to-Galois case as well as feedforward connections. This makes possible transforming Trivium stream cipher and increasing its keystream data rate by 27% without any penalty in area. The presented trans...

This paper presents a new stream cipher family whose output bits are produced by blocks. We particularly focus on the member of this family producing 128-bit blocks with a 256-bit key. The design is based on a new technique called crossing over which allows to vectorize stream ciphering by using nonlinear shift registers. These algorithms offer a very high cryptographic security and much higher...

At FSE 2004 two new stream ciphers VMPC and RC4A have been proposed. VMPC is a generalisation of the stream cipher RC4, whereas RC4A is an attempt to increase the security of RC4 by introducing an additional permuter in the design. This paper is the first work presenting attacks on VMPC and RC4A. We propose two linear distinguishing attacks, one on VMPC of complexity 2, and one on RC4A of compl...

In stream cipher cryptography a pseudorandom sequence of bits of length equal to the message length is generated. This sequence is then bitwise XORed (addition modulo 2) with the message sequence and the resulting sequence is transmitted. At the receiving end, deciphering is done by generating the same pseudorandom sequence and bitwise XORing the cipher bits with the random bits. The seed of th...

In symmetric-key cryptography, two parties share a secret key K to encrypt messages using a cipher. Symmetric encryption techniques are used to efficiently encrypt data. Two common types of ciphers are commonly used nowadays: block ciphers and stream ciphers. Block ciphers encrypt blocks of data (typically 64 or 128 bits) in a fixed key-dependent way. The design of block ciphers is a well-studi...