def encrypt_CBC(key, text):
block_size = 16
text_blocks = generate_blocks(pad(text), block_size)
initialisation_vector = b'\x00' * block_size
cipher_blocks = [initialisation_vector]
for i in range(len(text_blocks)):
xor = fixed_xor(cipher_blocks[i], text_blocks[i])
cipher_blocks.append(encrypt_ECB(key, xor, add_padding=False))
return "".join(cipher_blocks[1:])
def decrypt_CBC(key, text):
block_size = 16
cipher_blocks = generate_blocks(text, block_size)
initialisation_vector = b'\x00' * block_size
cipher_blocks.insert(0, initialisation_vector)
text_blocks = []
for i in range(len(cipher_blocks) - 1):
decrypted = decrypt_ECB(key, cipher_blocks[i + 1], strip_padding=False)
text_blocks.append(fixed_xor(cipher_blocks[i], decrypted))
return unpad("".join(text_blocks))
def repeating_key_xor(key, text):
return "".join([fixed_xor(text[i], key[i%len(key)]) for i in range(len(text))])
