There was a video of someone describing cryptography during a lecture with the example of a secret locked by Alice and sent to Bob. Bob has no way of opening Alice’s lock, so they simply add their lock and send it back to Alice. Then Alice removes her lock and sends the secret back to Bob, who now can remove their own lock and access the secret. What kind of cryptography is that? Does anyone know what lecture that wa…
> What kind of cryptography is that? It isn't. That is an example where a physical system that would work[‡] does not when applied to mathematics, given as an example where physical world analogies do not translate to useful mathematical methods. It is used as part of the journey towards understanding remote key exchange and public key cryptography, such lectures usually follow the rough pattern: 1. That two-lock phy…
I can't recall if symmetric ciphers are commutative or not. Specifically if:
f(f(x)) = x
g(g(x)) = x
f(g(f(x))) = g(x)