From: Technology Review

At the heart of Apple’s security architecture is the Advanced Encryption Standard algorithm (AES), a data-scrambling system published in 1998 and adopted as a U.S. government standard in 2001. After more than a decade of exhaustive analysis, AES is widely regarded as unbreakable. The algorithm is so strong that no computer imaginable for the foreseeable future—even a quantum computer—would be able to crack a truly random 256-bit AES key. The National Security Agency has approved AES-256 for storing top-secret data.