Homework 1

CSCE 813 – Farkas

Spring 2014

Score: 10 points

Due: January 23, 2014 2:00 am via dropbox

Consider the following cryptography protocol aiming to support the agreement of a shared key K_AB between Alice and Bob, using a trusted third party TTP.

In the protocol, A(B) is the identity of A(B), Cert_A(B) is the digital certificate of A(B), Sig_A(B){M} denotes that A(B) digitally signs message M, K_A(B) is the public key of A(B), K_AB is the shared secret key to be used between A and B, t is a time stamp, E(K,M) denotes the encryption of message M with K.

After each message explain what the recipient of the message knows and the level of trust.

1. Alice -> TTP: A, B

2. TTP -> Alice: Cert_A, Cert_B

3. Alice -> Bob: Cert_A, Cert_B, E(K_B, [Sig_A{( K_AB, t)}])

Show an attack where Bob can fool a third user, Pete, that Pete is sharing K_AB with Alice (not Bob).