Weak pseudorandom functions (wPRFs) found an important application as main building blocks for leakage-resilient ciphers (EUROCRYPT’09). Several security bounds, based on different techniques, were given to these stream ciphers. The security loss in these reduction-based proofs is always polynomial, but has not been studied in detail. The aim of this paper is twofold. First, we present a clear ...

Nowadays stream ciphers are the fastest among the encryption procedures, thus they are performed in many practical applications. Irregularly decimated generators are very simple sequence generators to be used as keystream generators in stream ciphers. In this paper, a linearisation method for the self-shrinking generator has been developed. The proposal defines linear structures based on cellul...

This paper looks at the possibility of combining a block cipher and a stream cipher to get a strong hybrid cipher. It includes two specific proposals for combining AES-128 and RC4-128 to get a cipher that takes a 256-bit key and is significantly faster than AES-256, and arguably more secure. One is immune to algebraic attacks.

Stream ciphers are widely used for online-encryption of arbitrarily long data, for example when transmitting speech-data between a mobile phone and a base station. An important class of stream ciphers are combiners with memory, with the E0 generator from the Bluetooth standard for wireless communication being their most prominent example. In this paper, we develop design principles for increasi...

In 2008 I. Dinur and A. Shamir presented a new type of algebraic attack on symmetric ciphers named cube attack. The method has been applied to reduced variants of stream ciphers Trivium and Grain128, reduced variants of the block ciphers Serpent and CTC and to a reduced version of the keyed hash function MD6. Independently a very similar attack named AIDA was introduced by M. Vielhaber. In this...

In 2008 I. Dinur and A. Shamir presented a new type of algebraic attack on symmetric ciphers named cube attack. The method has been applied to reduced variants of stream ciphers Trivium and Grain128, reduced variants of the block ciphers Serpent and CTC and to a reduced version of the keyed hash function MD6. Independently a very similar attack named AIDA was introduced by M. Vielhaber. In this...

Stream ciphers are cryptographic primitives that are used to ensure the privacy of a message that is sent over a digital communication channel. In this thesis we will present new cryptanalytic results for several stream ciphers. The thesis provides a general introduction to cryptology, explains the basic concepts, gives an overview of various cryptographic primitives and discusses a number of d...

T thesis presents new cryptanalysis results for several different stream cipher constructions. In addition, it also presents two new stream ciphers, both based on the same design principle. The first attack is a general attack targeting a nonlinear combiner. A new class of weak feedback polynomials for linear feedback shift registers is identified. By taking samples corresponding to the linear ...

To date, most applications of algebraic analysis and attacks on stream ciphers are on those based on linear feedback shift registers (LFSRs). In this paper, we extend algebraic analysis to non-LFSR based stream ciphers. Specifically, we perform an algebraic analysis on the RC4 family of stream ciphers, an example of stream ciphers based on dynamic tables, and investigate its implications to pot...

This paper considers modern secret-key block ciphers. The theory behind the design and analysis of modern block ciphers is explained, and the most important known attacks are outlined. Finally the Advanced Encryption Standard is discussed. 1 Block Ciphers Introduction In the last few thousands of years encryption algorithms, also called ciphers, have been developed and used [18,28]. Many of the...