AES Challenge

Here are some Rijndael 128-bit key 128-bit block AES challenge problems. No prizes will be given for solving them. Part I asks you to find the key (or more correctly, a key, since theoretically there is likely to be more than one correct key for each challenge, although not necessarily with the desired zero-padding) which causes a plaintext zero block (a block of 128 zero bits) to become encrypted to the given ciphertext. Part II asks the opposite--to find a key which causes a ciphertext block of zeros to decrypt to the given plaintext. I generated the keys by reading from /dev/random and did not record the keys except for the joke at the end of Part II, so I don't know the answers myself. Part III asks for plaintext-ciphertext collisions.

For key lengths less than 128, the key is padded on the left with zeros to be 128 bits total. Therefore, the challenges for each part start out trivial (zero key!) and get harder.

I used Brian Gladman's "new" AES implementation.

Send your results to kenta@mit.edu. Include in the subject line the phrase "AES Challenge" so that your message doesn't get lost in all the spam.

Part I: Decrypt these to get zero

Or you can encrypt a plaintext zero block to try to get the ciphertext.

Part II: Encrypt these to get zero

Part III: Plaintext-Ciphertext Partial Collisions

The challenge here is to find a plaintext-ciphertext block pair which agree on a large number of leading bits. Specifically, we want to minimize the binary value of PLAINTEXT xor CIPHERTEXT. There are two divisions: the first requires the use of the zero key, the second allows any non-zero key of your choice.

Zero key division: Current Record

Using the key consisting of 128 zero bits.

• Plain-text: 3355B261 9B61655A 63BF8E56 50A5FD7E
• Ciphertext: 3355B261 9B616E80 D5D5A192 6E7241DA
• XOR       : 00000000 00000bda b66a2fc4 3ed7bca4
• Found by: Jim Williams (2008)

Arbitrary non-zero key division: Current Record

• Key       : 19533d23 ff909ee3 64ba685f 3d089215
• Plain-text: 9a2400b7 d9df691f 0ef52ac3 407560df
• Ciphertext: 9a24008e 26d4ebae 220de0a0 60ce5f91
• XOR       : 00000039 ff0b82b1 2cf8ca63 20bb3f4e
• Found by: me

Here is a webpage that implements AES in Javascript to verify the collisions above.