A general construction for monoid-based knapsack protocols
Giacomo Micheli Michele Schiavina
We present a generalized version of the knapsack protocol proposed by D. Naccache and J. Stern at the Proceedings of Eurocrypt (1997). Our new framework will allow the construction of other knapsack protocols having similar security features. We will outline a very concrete example of a new protocol using extension fields of a finite field of small characteristic instead of the prime field $\mathbb{Z}/p\mathbb{Z}$, but more efficient in terms of computational costs for asymptotically equal information rate and similar key size.
keywords: polynomials over finite fields Naccache-Stern protocol. monoids Public key encryption knapsack protocols
Cryptanalysis of a noncommutative key exchange protocol
Giacomo Micheli
In the papers by Alvarez et al. and Pathak and Sanghi a non-commutative based public key exchange is described. A similiar version of it has also been patented (US7184551). In this paper we present a polynomial time attack that breaks the variants of the protocol presented in the two papers. Moreover we show that breaking the patented cryptosystem US7184551 can be easily reduced to factoring. We also give some examples to show how efficiently the attack works.
keywords: cryptanalysis finite fields. Cryptography non commutative protocols matrices

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