Updated according to code review feedback.
diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index e2542a1..f9849e2 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -42,3 +42,7 @@
class InvalidKey(Exception):
pass
+
+
+class InvalidToken(Exception):
+ pass
diff --git a/cryptography/hazmat/oath/hotp.py b/cryptography/hazmat/oath/hotp.py
index a04d0d4..a1f6274 100644
--- a/cryptography/hazmat/oath/hotp.py
+++ b/cryptography/hazmat/oath/hotp.py
@@ -12,28 +12,37 @@
# limitations under the License.
import struct
+from cryptography.exceptions import InvalidToken
import six
-from cryptography.hazmat.primitives import constant_time
+from cryptography.hazmat.primitives import constant_time, hmac
from cryptography.hazmat.primitives.hashes import SHA1
class HOTP(object):
- def __init__(self, secret, length, backend):
- self.secret = secret
- self.length = length
- self.backend = backend
+ def __init__(self, key, length, backend):
+
+ if len(key) < 16:
+ raise ValueError("Key length has to be at least 128 bits.")
+
+ if length < 6:
+ raise ValueError("Length of HOTP has to be at least 6.")
+
+ self._key = key
+ self._length = length
+ self._backend = backend
def generate(self, counter):
- sbit = self._dynamic_truncate(counter)
- foo = sbit % (10**self.length)
- return ('%s' % foo).zfill(self.length).encode()
+ truncated_value = self._dynamic_truncate(counter)
+ hotp = truncated_value % (10**self._length)
+ return "{0:0{1}}".format(hotp, self._length).encode()
def verify(self, hotp, counter):
- return constant_time.bytes_eq(self.generate(counter), hotp)
+ if not constant_time.bytes_eq(self.generate(counter), hotp):
+ raise InvalidToken("Supplied HOTP value does not match")
def _dynamic_truncate(self, counter):
- ctx = self.backend.create_hmac_ctx(self.secret, SHA1)
+ ctx = hmac.HMAC(self._key, SHA1(), self._backend)
ctx.update(struct.pack(">Q", counter))
hmac_value = ctx.finalize()
diff --git a/docs/hazmat/oath/hotp.rst b/docs/hazmat/oath/hotp.rst
index 614933f..1dee26b 100644
--- a/docs/hazmat/oath/hotp.rst
+++ b/docs/hazmat/oath/hotp.rst
@@ -17,18 +17,20 @@
This is an implementation of :rfc:`4226`.
- .. code-block:: python
+ .. doctest::
+ >>> import os
>>> from cryptography.hazmat.backends import default_backend
>>> from cryptography.hazmat.oath.hotp import HOTP
- >>> hotp = HOTP(secret, 6, backend=default_backend)
- >>> hotp.generate(0)
- 958695
- >>> hotp.verify("958695", 0)
- True
- :param secret: Secret key as ``bytes``.
- :param length: Length of generated one time password as ``int``.
+ >>> key = "12345678901234567890"
+ >>> hotp = HOTP(key, 6, backend=default_backend())
+ >>> hotp.generate(0)
+ '755224'
+ >>> hotp.verify("755224", 0)
+
+ :param bytes secret: Secret key as ``bytes``.
+ :param int length: Length of generated one time password as ``int``.
:param backend: A
:class:`~cryptography.hazmat.backends.interfaces.HMACBackend`
provider.
@@ -36,7 +38,7 @@
.. method:: generate(counter)
:param int counter: The counter value used to generate the one time password.
- :return: A one time password value.
+ :return bytes: A one time password value.
.. method:: verify(hotp, counter)
diff --git a/pytest.ini b/pytest.ini
index 77360d1..3f65e30 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -7,4 +7,3 @@
pbkdf2hmac: this test requires a backend providing PBKDF2HMACBackend
rsa: this test requires a backend providing RSABackend
supported: parametrized test requiring only_if and skip_message
- oath: this test requires a backend providing HMACBackend
diff --git a/tests/hazmat/oath/test_hotp.py b/tests/hazmat/oath/test_hotp.py
index cd06c79..8a5aebd 100644
--- a/tests/hazmat/oath/test_hotp.py
+++ b/tests/hazmat/oath/test_hotp.py
@@ -10,18 +10,41 @@
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
+from cryptography.exceptions import InvalidToken
+
+import os
import pytest
+
from cryptography.hazmat.oath.hotp import HOTP
+from cryptography.hazmat.primitives import hashes
from tests.utils import load_vectors_from_file, load_nist_vectors
vectors = load_vectors_from_file(
"oath/rfc-4226.txt", load_nist_vectors)
-@pytest.mark.oath
+@pytest.mark.supported(
+ only_if=lambda backend: backend.hmac_supported(hashes.SHA1()),
+ skip_message="Does not support HMAC-SHA1."
+)
+@pytest.mark.hmac
class TestHOTP(object):
+ def test_invalid_key_length(self, backend):
+ secret = os.urandom(10)
+
+ with pytest.raises(ValueError):
+ hotp = HOTP(secret, 6, backend)
+ hotp.generate(0)
+
+ def test_invalid_hotp_length(self, backend):
+ secret = os.urandom(16)
+
+ with pytest.raises(ValueError):
+ hotp = HOTP(secret, 4, backend)
+ hotp.generate(0)
+
@pytest.mark.parametrize("params", vectors)
def test_truncate(self, backend, params):
secret = params["secret"]
@@ -50,4 +73,13 @@
hotp = HOTP(secret, 6, backend)
- assert hotp.verify(hotp_value, counter) is True
+ assert hotp.verify(hotp_value, counter) is None
+
+ def test_invalid_verify(self, backend):
+ secret = b"12345678901234567890"
+ counter = 0
+
+ hotp = HOTP(secret, 6, backend)
+
+ with pytest.raises(InvalidToken):
+ hotp.verify(b"123456", counter)