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After a discussion about encryption, a friend of mine challenged me to crack a file he encrypted using AES with a 128bit key.
I know the file was originally a GIF image, so it should start with 'GIF8'. I'm wondering if it is possible to derive the password from this knowledge in a reasonable time (ie. a week or less).
Stealing the key in any way other than analyzing the encrypted file is not possible, as it defeats the point of the challenge.
If so, pointers would be welcome. I failed to find a decent flow-chart-like description of how the encryption of the first block works. I remember I had one from a course at Uni, but of course, it's nowhere to be found.
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AES 256 is virtually impenetrable using brute-force methods. While a 56-bit DES key can be cracked in less than a day, AES would take billions of years to break using current computing technology. Hackers would be foolish to even attempt this type of attack. Nevertheless, no encryption system is entirely secure.
With the right quantum computer, AES-128 would take about 2.61*10^12 years to crack, while AES-256 would take 2.29*10^32 years. For reference, the universe is currently about 1.38×10^10 years old, so cracking AES-128 with a quantum computer would take about 200 times longer than the universe has existed.
The EE Times points out that even using a supercomputer, a “brute force” attack would take one billion years to crack AES 128-bit encryption.
wvdschel, while I certainly wish you good luck, consider that if you solve this problem you'll be probably entitled to a Ph.D in computer science or mathematics. AES was designed to be extremely difficult to break (i.e. in the exponential order of the amount of bits) even if you know some minor details about the encrypted file.
Any attack that can lower the complexity from about 2 to the power of the bit-length of the key somewhat will be a great breakthrough. In the past, such attacks on DES (that merely lowered its strength by a few times) won their authors wide acclaim.
Read up on linear cryptanalysis of AES.
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