def test_remove_pkcs7_padding():
""" Set 2, Challenge 15 """
assert remove_pkcs7_padding('ICE ICE BABY\x04\x04\x04\x04') == 'ICE ICE BABY'
with pytest.raises(Exception):
remove_pkcs7_padding('ICE ICE BABY\x05\x05\x05\x05')
with pytest.raises(Exception):
remove_pkcs7_padding('ICE ICE BABY\x01\x02\x03\x04')
def cbc_padding_oracle(ciphertext, iv, padding_valid_fn):
""" Decrypt a CBC encrypted ciphertext using a padding oracle
:param ciphertext: Ciphertext to decrypt
:param padding_valid_fn: Function that decrypts the ciphertext, checks the padding, and returns the status of the padding (True or False)
:return: Recovered plaintext
"""
block_size = 16
ct_blocks = list(chunks(iv + ciphertext, block_size))
pt = ''
for two_blocks in chunks(ct_blocks[::-1], 2, adv=1):
try:
pt = cbc_padding_attack_block(two_blocks[1], two_blocks[0], padding_valid_fn) + pt
except IndexError:
break
return remove_pkcs7_padding(pt)