AESScan
-------

This is a command line utility to search binary data for possible AES keys.
You will need one or more ciphertexts encrypted using the key that is
suspected to appear in the binary file. The ciphertexts are used to attempt
decryption, and check if the resulting plaintext makes any sense. The
plaintext is assumed to contain either a large number of zero bytes (typical
for binary data) or a very small number of uncommon control characters
(typical for text files). So it's not possible to use this tool on random data
that has been encrypted, or data that has been encrypted multiple times.

The command line syntax is:

    aesscan -s binary.bin [options] ciphertext1.bin ciphertext2.bin ...

Where binary.bin is the file to search for keys in. Supported options are:

   -c CIPHER   Set the cipher to use:
                    0   AES128 with CBC (default)
                    1   AES128 with ECB
                    2   AES256 with CBC
                    3   AES256 with ECB
   -p PADDING  Set the padding to use:
                    0   PKCS#5 (default)
                    1   Simply throw away the last block
                    2   No padding
   -l LEN      Try to decrypt only up to LEN bytes in the FILES
   -o OFFSET   Start from the given byte offset in the FILES

The -o and -l options are parsed from left to right. An -o or -l option must
occur before the ciphertext file(s) it should to apply to.

AES is typically used with a block mode and a padding. CBC and PKCS#7
is the most common block mode and padding, so these are the defaults.
When the padding type is unknown, it is useful to use "throw away" option
(number 1) which will simply skip the last encrypted block. This option will
obviously only work if the data is more than 16 bytes, which is the block
size of AES (regardless of key size).

For block modes other than ECB, this tool will assume that the first 16 bytes
is the Initialization Vector (IV) for the following data. This is the most
common way of encoding encrypted AES data.