Vulnerabilities of some semidirect products in Diffie-Hellman key exchanges

The Diffie-Hellman key exchange protocol introduced in 1976 allows two users, Alice and Bob, to establish a shared secret key K over insecure communication channels. With the rise of quantum computers, the protocol is in danger of becoming easily breakable. In response, several modified versions of Diffie-Hellman have been proposed claiming to be resistant to attacks performed by quantum computers.

Two such protocols and use of a semidirect product creating a modified version of a Discrete Logarithm problem to provide security for Alice and Bob.

Regardless of choosing a tropical semiring or a free nilpotent p-group, these protocols prove not only vulnerable to quantum attacks, but they can be attacked by a classical computer. By exploiting each of the platforms, an eavesdropper Eve needs only to figure out how to mimic Alice's contribution to the shared secret key without needing to copy Alice's exact operations. By doing so, Eve can efficiently recover the shared secret key K.

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