  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.
