Cryptopals Set 2 Exercise 16 Simplified

cryptopals_1_16_simplified.py

def crack():
    first_block = bytearray('A' * AES.block_size)
    second_block = bytearray("AadminAtrueA")

    plaintext = first_block + second_block
    ciphertext = encryption_oracle(plaintext)

    # We 'know' the prefix is two blocks long
    offset = 32

    # Change the first byte in first_block 'A' so we change the first byte in
    # second_block to be ';'
    ciphertext[offset] = bytes(
        xor(
            bytearray(chr(ciphertext[offset])), 
            xor(bytearray("A"), bytearray(";"))
        )
    )
    # Change the 7th byte in first_block 'A' so we change the first byte in
    # second_block to be '='
    ciphertext[offset + 6] = bytes(
        xor(
            bytearray(chr(ciphertext[offset + 6])), 
            xor(bytearray("A"), bytearray("="))
        )
    )
    # Change the 12th byte in first_block 'A' so we change the first byte in
    # second_block to be ';'
    ciphertext[offset + 11] = bytes(
        xor(
            bytearray(chr(ciphertext[offset + 11])),
            xor(bytearray("A"), bytearray(";"))
        )
    )
    return is_admin(ciphertext)