Suppose the following.
Someone wishes to encrypt a message so it is not intercepted. With traditional ciphers, if the key is guessed correctly, the message is revealed. This cipher is similar– except that if an incorrect, but intentionally weaker key is guessed, a valid decoy message is revealed to deceive the adversary.
ciphertext + realPassword = "We attack at 14:30 sharp."
chiphertext + weakPassword = "We attack at dawn."
Does such a cipher exist, and if so what is its name.