Simple implementation of Advanced Encryption Standards, with 128-, 192-, and 256-bit key lengths. Usage: 3 mandatory arguments. Arg1 is either 'e' for encrypt or 'd' for decrypt. Arg2 is 16 byte message in hexadecimal (must be exactly 16 bytes, fewer should be 0-padded). Arg3 is the key in hexadecimal. Must be 16, 24, or 32 bytes.