Requirements: pip3 install --user pycrypto

File insecure_hash implements the hash function hash_string.

• If a message m consists of two blocks B1;B2 of 128 bits, the hash is computed as AES-decrypt(B1, B2): i.e. it decrypts the block B1 using B2 as key.
• If the message consists of three blocks B1;B2;B3, the hash is computed as AES-decrypt(AES-decrypt(B1, B2), B3)
• If the message consists of n blocks B1;B2;B3;...Bn, the hash is computed as AES-decrypt(... AES-decrypt(AES-decrypt(B1, B2), B3)..., Bn)

The message is padded with " " to be block aligned, e.g. if the length of the message is 200 bits, then 7 spaces (56 bits) are appended to the message before computing the hash.

This hash function is not secure. In particular it is not weak collision resistant. Complete the stub in collision.py, implementing the function find_collision(message) that finds a collision. Do not brute force.

To test your solution execute ./test.py.