Modulo Errors

Another day, another cryptographic protocol analysis writeup for Everything2. This time I covered the type flaw attack; a particularly devious vulnerability that is invisible to many formal analytic techniques.

I’ve added some more content to e2 from the formal analysis of cryptographic protocols course I’m taking, related to the problem of authentication via shared secrets.

Authentication sets notation and discusses one-way identity verification such as central locking for cars. The challenge-response protocol and the replay attack are included.

Mutual authentication demonstrates the reflection attack on running challenge-response in both directions; three-pass mutual authentication is introduced to resolve this (at the price of some extra complexity).

A brief mention of Massey-Omura encryption caught my eye as I was chasing references for the SEA algorithm (a method for counting points on elliptic curves over prime fields); following it gave me a bit of a break from geometry and I’ve written up the main ideas over on E2. It’s mostly in lay terms (featuring the usual cast of Alice, Bob, Eve and Mallory posting boxes to each other), but the mathematics of the three-pass system is covered towards the end. Specifically, I outline how factorisation isn’t a suitable technique but (assuming it’s as hard as everyone suspects) the discrete logarithm problem is.

I’ll also be attending an Informatics course, Formal Analysis of Cryptographic Protocols which starts on Thursday. It’s unlikely to have any direct bearing on my work but it sounds interesting and most interest in number theory outside academia is connected to crypto, so it’s always worth knowing more!