Our next idea for fixing ap3.0 is naturally to encrypt the password. By encrypting the password, we can prevent
someone from learning your password. If we assume people share a symmetric secret key, KA-B, then you can encrypt the
password and send your identification message and your encrypted password to others. They then decrypts the password
and, assuming the password is correct, authenticates you.
While it is true that ap3.1 prevents others from learning your password, the use of cryptography here does not solve
the authentication problem. Your receiver is subject to a playback attack.
The use of an encrypted password in ap3.1 doesn't make the situation manifestly different from that of protocol ap3.0.
