"""Attack block using side-channel leak in padding oracle."""
c2 = ciphertext[16:32]
plaintext = b""
dc_string = b""
h = 15
for i in range(1, 17):
for j in range(256):
c1 = b"A" * h + bytes([j])
if dc_string:
for c in dc_string[::-1]:
c1 += bytes([c ^ i])
if padding_validation(c1 + c2):
dc = j ^ i
dc_string += bytes([dc])
plaintext += bytes([dc ^ ciphertext[h]])
break
h -= 1
return plaintext[::-1]
IV = generate_bytes(16)
KEY = generate_bytes(16)
ciphertext = IV + padding_oracle()
plaintext = b""
for i in range(0, len(ciphertext) - 16, 16):
plaintext += attack_block(ciphertext[i:i + 32])
print(plaintext)
def extract_secret(oracle, offset, keysize):
"""Extract secret text from encryption oracle with a known offst and keysize."""
plaintext = b""
# iterate over the blocksize
for i in range(0, len(oracle(b"A" * offset + b"")[16:]), keysize):
h = keysize - 1
for j in range(keysize):
block = oracle(b"A" * offset + b"A" * h)[16:][i:i + keysize]
byte_dict = {}
for k in range(127):
byte_dict[k] = oracle(b"A" * offset + b"A" * h + plaintext +
bytes([k]))[16:][i:i + keysize]
for key, value in byte_dict.items():
if block == value:
plaintext += bytes([key])
h -= 1
return plaintext
def extract_prefix_secret():
"""Iterate over offsets from 0-16 returning secret when output != b''."""
for i in range(16):
if extract_secret(encryption_oracle, i, 16) != b"":
return extract_secret(encryption_oracle, i, 16)
KEY = generate_bytes(16)
RANDOM_PREFIX = generate_bytes(16)
# print(extract_prefix_secret())