Is there a cipher that yields two separate but valid results depending on the key?

Question

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.

So

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.

Answer 1

Honey Encryption does even better than what you are asking for. With honey encryption, every key from the key space results in a valid looking ciphertext. This primitive is only just now starting to be understood with applications also being developed. One target the inventors are looking at is password databases.