Final answer:
An attacker finding a functionally equivalent encryption and decryption algorithm without key learning represents a cryptographic breakthrough, potentially altering many existing cryptographic systems and practices.
Step-by-step explanation:
If an attacker discovers a functionally equivalent algorithm for encryption and decryption that operates without the need to learn the key, this could be described as a cryptographic breakthrough. This could potentially undermine many current encryption schemes that rely on the secrecy of key exchange or key generation processes. In cryptography, the requirement of a key is fundamental to the security of an encryption algorithm, so a method that does not require a key could result in significant changes to cryptographic practices and security models.