Countering chosen-ciphertext attacks against noncommutative polly cracker-type cryptosystems.

In [2], Stanislav Bulygin presents a chosen-ciphertext attack against certain instances of noncommutative polly cracker-type cryptosystems which were proposed in [7] and [9]. In this article, we present generalized versions of this attack, which can be used against virtually all polly cracker-type cryptosystems. We then present a simple but effective techique to counter these attacks. We also present a technique to counter an adaptive chosen-ciphertext attack which was first described by Neil Koblitz in [8]