def test_decrypt_bytes_not_padded_raises(self):
b = b"\x00\x01\x00\x01\x23"
iv = b"\x03\x03"
cbc = CBCMode(
blksize=2,
encrypt_blk=self.mock_fun,
decrypt_blk=self.mock_fun,
iv=iv,
)
with self.assertRaises(ValueError):
cbc.decrypt(b)
def is_admin(encrypted: bytes, blksize: int = 16) -> bool:
"""
params:
encrypted: message encrypted using `encryption_oracle()`
blksize: blocksize used by `encryption_oracle()`
returns:
True if decrypted message contains ";admin=true;", False otherwise
"""
cipher = AES.new(CONSISTENT_KEY, AES.MODE_ECB)
cbc = CBCMode(blksize=blksize,
encrypt_blk=cipher.encrypt,
decrypt_blk=cipher.decrypt,
iv=CONSISTENT_IV)
padded = cbc.decrypt(encrypted)
decrypted = PKCS7Padding.unapply(padded)
return b";admin=true;" in decrypted
def test_encrypt_decrypt_integration_case(self):
key = b"YELLOW SUBMARINE"
iv = b"THIS IS 16 BYTES"
cipher = AES.new(key, AES.MODE_ECB)
cbc = CBCMode(
blksize=16,
encrypt_blk=cipher.encrypt,
decrypt_blk=cipher.decrypt,
iv=iv,
)
plaintext = (b"Lorem ipsum dolo"
b"r sit amet, cons"
b"ectetur adipisci"
b"ng elitAAAAAAAAA")
encrypted = cbc.encrypt(plaintext)
decrypted = cbc.decrypt(encrypted)
self.assertEqual(plaintext, decrypted)
def validate_ascii(encrypted: bytes) -> bytes:
"""
params:
encrypted: message encrypted using `aes_cbc()`
returns:
decrypted bytes if they contain extended ascii characters,
None otherwise
"""
cipher = AES.new(key, AES.MODE_ECB)
cbc = CBCMode(blksize=blksize,
encrypt_blk=cipher.encrypt,
decrypt_blk=cipher.decrypt,
iv=key)
padded = cbc.decrypt(encrypted)
decrypted = PKCS7Padding.unapply(padded)
for c in decrypted:
if c >= 128:
return decrypted
return None
def valid_padding(encrypted: bytes, iv: bytes) -> bool:
"""
params:
encrypted: encrypted message
iv: IV used to encrypt `encrypted`
returns:
True if decryption of `encrypted` has valid padding
False otherwise
"""
blksize = len(CONSISTENT_KEY)
cipher = AES.new(CONSISTENT_KEY, AES.MODE_ECB)
cbc = CBCMode(blksize=blksize,
encrypt_blk=cipher.encrypt,
decrypt_blk=cipher.decrypt,
iv=iv)
decrypted = cbc.decrypt(encrypted)
try:
PKCS7Padding.unapply(decrypted)
return True
except InvalidPaddingException:
return False
def main():
"""
decrypt contents of a file encrypted using AES-128 in CBC mode
"""
key = b"YELLOW SUBMARINE"
iv = bytes(16)
cipher = AES.new(key, AES.MODE_ECB)
cbc = CBCMode(
blksize=16,
encrypt_blk=cipher.encrypt,
decrypt_blk=cipher.decrypt,
iv=iv
)
input_filename = os.path.join(pathlib.Path(__file__).parent, "input")
with open(input_filename, 'r') as input_file:
base64_str = input_file.read()
base64_bytes = base64_str.replace('\n', '').encode("utf-8")
encrypted = base64.decodebytes(base64_bytes)
message = cbc.decrypt(encrypted)
print(message.decode("utf-8", errors="ignore"))