Dipanwita Roy Chowdhury
SymSum: Symmetric-Sum Distinguishers Against Round Reduced SHA3
In this work we show the existence of special sets of inputs for which the sum of the images under SHA3 exhibits a symmetric property. We develop an analytical framework which accounts for the existence of these sets. The framework constitutes identification of a generic property of iterated SPN based functions pertaining to the round-constant addition and combining it with the notion of m−fold vectorial derivatives for differentiation over specially selected subspaces. Based on this we propose a new distinguisher called SymSum for the SHA3 family which penetrates up to 9 rounds and outperforms the ZeroSum distinguisher by a factor of four. Interestingly, the current work is the first analysis of SHA3/Keccak that relies on round-constants but is independent of their Hamming-weights.
Key Mixing in Block Ciphers through Addition modulo $2^n$
The classical technique to perform key mixing in block ciphers is through exclusive-or (exor). In this paper we show that when the $n$-bit key is mixed in a block cipher of size $n$ bits via addition modulo $2^n$, the bias of the linear approximations falls exponentially fast. Experimental results have been provided to show that such a scheme cannot be cryptanalyzed using Linear Cryptanalysis.
Design and Analysis of a Robust and Efficient Block Cipher using Cellular Automata
Cellular Automaton (CA) has been shown to be capable of generating complex and random patterns out of simple rules. There has been constant efforts of applying CA to develop ciphers, but the attempts have not been successful. This paper describes how repeated application of simple CA transforms may be used to achieve confusion and diffusion, needed in block ciphers. The components have been evaluated for their robustness against conventional cryptanalysis and the results have been found to be comparable to standards. Finally, the parts are assembled in an unconventional way to construct a self-invertibe CA based round, which is resistant against linear and differential cryptanalysis and yet can be efficiently implemented.