cryptography – Symmetric encryption – given plain text, produce cipher text without key


Suppose Alice and Bob are communicating using a peer-reviewed symmetric encryption algorithm such as AES-256. Bob possesses a private encryption key to decode messages from Alice, but Alice does not have this key.

If Alice has plain text ready to encrypt and send to Bob, is it computationally feasible for Alice to produce cipher text that would be successfully decrypted by Bob without knowing his encryption key?