how many combinations needed to decode AES-256 key?

Question

How many combinations needed to decode AES-256 key?

I am not very good in cryptography but I think its something like Combination 256 of 16. Its not too much.

IF use all worlds computing power what time needed for decoding?

Answer 1

If you were simply brute forcing every possible key, there would be 2^256 keys you need to try. You'd expect to find it after going through (on average) half of the keys, so average expected number of attempts would be 2^255. This is a Really Big Number. If every atom on earth (about 1.3 * 10^50 atoms) was a computer that could try ten billion keys a second, it would still take about 2.84 billion years. Brute-forcing is simply not possible - you'd need to find a weakness in the algorithm that lets you take a short-cut here.