Protecting the confidentiality in large databases without degrading their performance is a challenging problem, especially when encryption and decryption must be performed at the database-level or at the application-level. We here focus on symmetric ciphers for database encryption since they are the only type of ciphers with acceptable performance for most applications. We point out that stream...

Stream ciphers are cryptographic primitives that ensure the confidentiality of communications. In this thesis, we study several attacks on stream ciphers. For practical applications, the candidates of stream ciphers of NESSIE and eSTREAM projects are scrutinized. Firstly, the algebraic attacks on SOBER-t32 and SOBER-t16 stream ciphers are performed under the assumption that the stuttering phase...

I the world of cryptography, stream ciphers are known as primitives used to ensure privacy over a communication channel. One common way to build a stream cipher is to use a keystream generator to produce a pseudorandom sequence of symbols. In such algorithms, the ciphertext is the sum of the keystream and the plaintext, resembling the one-time pad principal. Although the idea behind stream ciph...

Stream ciphers play an important role in symmetric cryptology because of their suitability in high speed applications where block ciphers fall short. A large number of fast stream ciphers or pseudorandom bit generators (PRBGs) can be found in the literature that are based on arrays and simple operations such as modular additions, rotations and memory accesses (e.g. RC4, RC4A, Py, Py6, ISAAC etc...

The ease of programming offered by the CUDA programming model attracted a lot of programmers to try the platform for acceleration of many non-graphics applications. Cryptography, being no exception, also found its share of exploration efforts, especially block ciphers. In this contribution we present a detailed walk-through of effective mapping of HC-128 and HC-256 stream ciphers on GPUs. Due t...

Received May 5 th , 2012 Revised May 31 st , 2012 Accepted June 2 nd , 2012 In open literature there is a lack of focus on Shannon‟s secrecy of ciphers as a security measurement of symmetric key encryption, hence in this research, Shannon‟s theories on secrecy of ciphers were used to calculate the average secrecy of each symmetric cipher used in this research. All secrecy and performance analys...

In this paper we model a class of stream and block ciphers as systems (ordinary) explicit difference equations over finite field. We call “difference ciphers” show that application interest, for example LFSRs with combiner, Trivium KeeLoq , belong to the class. By using Difference Algebra, is, formal theory equations, can properly define study important properties these ciphers, such their inve...

In this paper, we describe a cache-timing attack against the stream cipher HC-256, which is the strong version of eStream winner HC128. The attack is based on an abstract model of cache timing attacks that can also be used for designing stream ciphers. From the observations made in our analysis, we derive a number of design principles for hardening ciphers against cache timing attacks.

Abstract Recent lightweight hardware-based stream cipher designs keep an external non-volatile internal state that is not part of the cipher’s hardware module. The purpose these so-called small-state ciphers to size and power consumption low. We propose a random oracle model for ciphers. This will allow us analyse recent designs’ resistance against generic attacks and, in particular, time-memor...

In this paper, we propose an algebraic attack on stream ciphers. Starting from a well-known due to Courtois and Meier, design especially effective against nonlinear filter generators. First, test it two toy ciphers then show that the level of security WG-PRNG, one submitted NIST competition Lightweight Cryptography, is less than claimed until now.