Elcomsoft, which provides password recovery software and security audits, said it was able to decrypt an image of the data on iOS 4 devices. But the firm said it could only do so if it had the iPhone or iPad itself, as some of the encryption keys are stored in the hardware.
Apple uses the Advanced Encryption Standard, with a 256-bit key. The length of the key is usually considered strong enough that even law-enforcement agencies would have trouble breaking it. A "brute force" attack, using every possible key combination, would take billions of years for even the fastest computer to do.