[ACCEPTED]-Is it possible to reverse engineer AES256?-cryptanalysis

Simple answer: NO.

This has been tested, and 9 mentioned in the Wiki link.

A related-key 8 attack can break up to 9 rounds of 256-bit 7 AES. A chosen-plaintext attack can break 6 8 rounds of 192- and 256-bit AES, and 5 7 rounds of 128-bit AES, although the workload 4 is impractical at 2¹²⁸ - 2¹¹⁹.

Or put it another 3 way: you have a better chance of being struck 2 by lighting... on the same day you win the 1 Lottery, than breaking it!

This is called a known-plaintext attack. A good cipher like AES 1 should be immune to it, as the others explained.

If $pass is actually a password and not a 256-bit 9 key, you may be in luck.

While it is far 8 from trivial to perform, a brute-force attack 7 against a normal password is much faster 6 than brute-forcing a 256-bit key.

So modify 5 one of the many password-brute-forcing tools, and 4 you have a attack that (depending on the 3 strength of the password) might take weeks 2 to several years - but that is fast compared 1 to 3x10^51 years...

Another quote, from Wikipedia:

AES permits the use 14 of 256-bit keys. Breaking a symmetric 13 256-bit key by brute force requires 2^128 12 times more computational power than a 11 128-bit key. A device that could check 10 a billion billion (10^18) AES keys per second 9 would require about 3 x 10^51 years to 8 exhaust the 256-bit key space.

Brute forcing 7 when you know the original text might be 6 faster but still, 3 x 10^51 years is a long 5 time. Plus there's the problem of probably 4 not having a device that can check a billion 3 billion (10^18) keys/second.

In short: everything 2 is possible, but this is not feasible in 1 the world we are now living in.

You could brute force it, but it would take 3 a long time. As in decades or even longer. That's 2 the point of encryption algorithms like 1 AES.

AES, like all good crypto algorithms, doesn't 5 rely on security through obscurity.

In other words, there are no "secrets" in 4 the code, so you having the code won't help 3 you particularly.

Known plaintext is a separate 2 issue, which I don't know much about so 1 I'll leave that up to the other answerers.

Of course not - the only approach is brute 3 force. Do you really think NIST is so stupid 2 as to choose a cipher that is so easily 1 cracked for a new standard?

with the power of super computers the time 2 to crash AES encryption with be dramatically 1 shortened.... I heard...

2x2^256 possible combinations is a lot to 14 bruteforce. But bruteforcing is the only 13 way. It would actually take about 3 decades. AES 12 is the best Encryption possible right now 11 I'd say. But that would only take that much 10 time using a CPU. Because GPU's (Graphic 9 Processing Units) are strictly math based, people 8 have been making programs that only use 7 the GPU to crack math based algorithms much 6 more quickly than a CPU could. In other 5 words AES might not last 3 decades. If only 4 eternity codes were possible. Well looks 3 like dynamic encryption may be the only 2 way people can really hide their information 1 in the near future.