New answers tagged mac
3
One of the factors that determines how hard it is to forge a MAC for a given message is how long the MAC is. If it's 1 bit long, you can definitely produce the correct MAC in two tries.
$2^n$ is the number of possible bit-strings of length $n$; $1/2^n$ is the probability that any random bit-string happens to be the MAC (of length $n$) for a given message ...
9
I'll assumme All ciphered blocks means the same as ciphertext for CBC-Encryption with implicit zero IV, while CBC-MAC is the last block of that.
All ciphered blocks is unsafe as a message authenticator for messages longer than one block, for it succumbs to a trivial attack (here with two blocks):
Eve intercepts message $M=M_0||M_1$ and its authenticator ...
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