While educating my self I'm having hard time to understand what an 128 bit AES key actually means? Is it a key length or entropy?
Please explain to me trough following example (assuming AES):
Password length in characters (L) = 20 (characters)
Symbols used (N) = 95 (ASCII set)
Entropy = log2 (N^L) = 128 (is this what is called 128bit AES key?)
Key length = L * 8bits = 160 bit key length ? (is this supposed to be 160bit AES key?)
When somebody says that he's using 128bit AES key, I want to know to what is he referring to, a key length or entropy?