def test_challenge10(self):
ciphertext = base64_to_bytes(read('10.txt'))
key = 'YELLOW SUBMARINE'
iv = '\x00' * 16
plaintext = cbc_decrypt(ciphertext, key, iv)
ciphertext = cbc_encrypt(plaintext, key, iv)
plaintext2 = cbc_decrypt(ciphertext, key, iv)
self.assertEquals(plaintext, plaintext2)
def verify_decrypt(enc):
print(enc)
if enc == None or enc == "":
return False
try:
plain = crypto.cbc_decrypt(enc.decode("hex"), master_key)
return True
except:
return False
def echo(self, message):
s = pow(self.A, self.b, self.p)
key = Sha1Hash().update(to_bytes_le(s)).digest()[:16]
ciphertext = message[:-16]
iv = message[-16:]
plaintext = crypto.cbc_decrypt(ciphertext, key, iv)
self.messages.append(plaintext)
iv = crypto.iv()
return crypto.cbc_encrypt(plaintext, key, iv) + iv
def echo(self, message):
response = self.receiver.echo(message)
# Our malicious middleman has returned p to Alice.
# Alice uses this value as B.
# Alice generates her key with: (B ** a) % p
# Because B == p, p ** a will always be an exact multiple of p so the
# mod value will be 0 regardless of the value of a.
key = Sha1Hash().digest()[:16]
ciphertext = message[:-16]
iv = message[-16:]
plaintext = crypto.cbc_decrypt(ciphertext, key, iv)
self.messages.append(plaintext)
return response
def send(self, receiver, message):
self.messages.append(message)
B = receiver.handshake(self.p, self.g, self.A)
s = pow(B, self.a, self.p)
key = Sha1Hash().update(to_bytes_le(s)).digest()[:16]
iv = crypto.iv()
ciphertext = crypto.cbc_encrypt(message, key, iv) + iv
returned_message = receiver.echo(ciphertext)
returned_ciphertext = returned_message[:-16]
returned_iv = returned_message[-16:]
decrypted = crypto.cbc_decrypt(
returned_ciphertext,
key,
returned_iv
)
return decrypted
def is_admin(ciphertext, key, iv):
decrypted = cbc_decrypt(ciphertext, key, iv)
return ';admin=true;' in decrypted
def is_padding_valid(ciphertext, key, iv):
try:
cbc_decrypt(ciphertext, key, iv)
return True
except PaddingError:
return False
def is_admin_cbc(ciphertext, key):
decrypted = crypto.cbc_decrypt(ciphertext, key, key)
if not all(ord(c) < 128 for c in decrypted):
raise ValueError('Invalid message ' + decrypted)
return ';admin=true;' in decrypted