I've been given a AES-CBC-MAC, a message and the IV. I don't know the key. Given a second message I am supposed to derive the IV and create a valid MAC.
I believe I've successfully created the second IV,
(Message1 XOR IV1) XOR Message2. However I'm not able to create a valid MAC - but this is where I'm unsure if I have misunderstood something: Given the same key for both messages, shouldn't MAC1 and MAC2 match given how I've created IV2?
And yes, as you've certainly guessed, this is a homework question. I've been driving myself crazy trying to figure this out, but I've come to the realisation that my understanding of AES-CBC-MAC is lacking.