Station-to-Station Protocol

Definition

The Station-to-Station protocol is a popular authenticated key exchange.

Theory

In a two-party authenticated key exchange, the legitimate parties can compute a secret key, while at the same time being certain about the authenticity of the parties with whom they exchange a key. The scheme must, in particular, be secure against a man-in-the-middle attack.

A popular authenticated version of the Diffie–Hellman key exchange protocol is the Station-to-Station protocol. It was proposed by Diffie–van Oorschot–Wiener [ 1].

Let 〈g〉 be a suitable finite cyclic group of large enough order in which the computational Diffie–Hellman problem is (assumed to be) hard. We assume that q (not necessarily prime) is a multiple of the order of g and is publicly known. Let sign _A (m) indicate the digital signature of the bitstring m by party A. So, sign _A (m) can be verified using the public key of A. Let E _k (m) be a conventional encryption of the bitstring m using the conventional key k. (If kis...