[nybble41]

> A brute-force attack capable of testing 2^128 keys can break any AES-128 key with certainty.

One minor caveat: You have to be able to recognize when you've found the right key. If the message is short (less than the key size) then it is likely that there are multiple keys that can decode the ciphertext to a plausible message and you have no way to know which one was correct. This is why an ideal One-Time Pad is considered unbreakable even by brute force: For any possible message of size less than or equal to the ciphertext there exists a key which will decode the ciphertext into that message.