Is it possible to break AES-128 ECB if you are given a ciphertext and a small portion of the key? If you are given the ciphertext and the first half bytes (8 bytes) of the encryption key (key is 16 bytes in total), can you use this to break AES-128 ECB encryption and determine the last 8 bytes of the encryption key? (As opposed to trying all 256^8 possibilities for the last 8 bytes of the key, which is A LOT of possibilities and would take days/months to compute)
You can't use it to "break the encryption", but you can guess at the remaining 8 bytes of the key. The remaining 8 bytes should be feasible to find, especially if you can run the search in parallel.