diff --git a/docs/reference/google.auth.crypt.rst b/docs/reference/google.auth.crypt.rst
new file mode 100644
index 0000000..7f8c0f8
--- /dev/null
+++ b/docs/reference/google.auth.crypt.rst
@@ -0,0 +1,7 @@
+google.auth.crypt module
+========================
+
+.. automodule:: google.auth.crypt
+    :members:
+    :undoc-members:
+    :show-inheritance:
diff --git a/docs/reference/google.auth.rst b/docs/reference/google.auth.rst
index 0533449..4c39cb9 100644
--- a/docs/reference/google.auth.rst
+++ b/docs/reference/google.auth.rst
@@ -6,3 +6,10 @@
     :undoc-members:
     :show-inheritance:
 
+Submodules
+----------
+
+.. toctree::
+
+   google.auth.crypt
+
diff --git a/docs/reference/google.oauth2.rst b/docs/reference/google.oauth2.rst
new file mode 100644
index 0000000..fb67d27
--- /dev/null
+++ b/docs/reference/google.oauth2.rst
@@ -0,0 +1,8 @@
+google.oauth2 package
+=====================
+
+.. automodule:: google.oauth2
+    :members:
+    :undoc-members:
+    :show-inheritance:
+
diff --git a/google/auth/_helpers.py b/google/auth/_helpers.py
new file mode 100644
index 0000000..2d3b653
--- /dev/null
+++ b/google/auth/_helpers.py
@@ -0,0 +1,65 @@
+# Copyright 2015 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helper functions for commonly used utilities."""
+
+import six
+
+
+def to_bytes(value, encoding='utf-8'):
+    """Converts a string value to bytes, if necessary.
+
+    Unfortunately, ``six.b`` is insufficient for this task since in
+    Python 2 because it does not modify ``unicode`` objects.
+
+    Args:
+        value (Union[str, bytes]): The value to be converted.
+        encoding (str): The encoding to use to convert unicode to bytes.
+            Defaults to "utf-8".
+
+    Returns:
+        bytes: The original value converted to bytes (if unicode) or as
+            passed in if it started out as bytes.
+
+    Raises:
+        ValueError: If the value could not be converted to bytes.
+    """
+    result = (value.encode(encoding)
+              if isinstance(value, six.text_type) else value)
+    if isinstance(result, six.binary_type):
+        return result
+    else:
+        raise ValueError('{0!r} could not be converted to bytes'.format(value))
+
+
+def from_bytes(value):
+    """Converts bytes to a string value, if necessary.
+
+    Args:
+        value (Union[str, bytes]): The value to be converted.
+
+    Returns:
+        str: The original value converted to unicode (if bytes) or as passed in
+            if it started out as unicode.
+
+    Raises:
+        ValueError: If the value could not be converted to unicode.
+    """
+    result = (value.decode('utf-8')
+              if isinstance(value, six.binary_type) else value)
+    if isinstance(result, six.text_type):
+        return result
+    else:
+        raise ValueError(
+            '{0!r} could not be converted to unicode'.format(value))
diff --git a/google/auth/crypt.py b/google/auth/crypt.py
new file mode 100644
index 0000000..d347600
--- /dev/null
+++ b/google/auth/crypt.py
@@ -0,0 +1,229 @@
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Cryptography helpers for verifying and signing messages.
+
+Uses the ``rsa``, ``pyasn1`` and ``pyasn1_modules`` packages
+to parse PEM files storing PKCS#1 or PKCS#8 keys as well as
+certificates. There is no support for p12 files.
+
+The simplest way to verify signatures is using :func:`verify_signature`::
+
+    cert = open('certs.pem').read()
+    valid = crypt.verify_signature(message, signature, cert)
+
+If you're going to verify many messages with the same certificate, you can use
+:class:`Verifier`::
+
+    cert = open('certs.pem').read()
+    verifier = crypt.Verifier.from_string(cert)
+    valid = verifier.verify(message, signature)
+
+
+To sign messages use :class:`Signer` with a private key::
+
+    private_key = open('private_key.pem').read()
+    signer = crypt.Signer(private_key)
+    signature = signer.sign(message)
+
+"""
+
+from pyasn1.codec.der import decoder
+from pyasn1_modules import pem
+from pyasn1_modules.rfc2459 import Certificate
+from pyasn1_modules.rfc5208 import PrivateKeyInfo
+import rsa
+import six
+
+from google.auth import _helpers
+
+_POW2 = (128, 64, 32, 16, 8, 4, 2, 1)
+_CERTIFICATE_MARKER = b'-----BEGIN CERTIFICATE-----'
+_PKCS1_MARKER = ('-----BEGIN RSA PRIVATE KEY-----',
+                 '-----END RSA PRIVATE KEY-----')
+_PKCS8_MARKER = ('-----BEGIN PRIVATE KEY-----',
+                 '-----END PRIVATE KEY-----')
+_PKCS8_SPEC = PrivateKeyInfo()
+
+
+def _bit_list_to_bytes(bit_list):
+    """Converts an iterable of 1s and 0s to bytes.
+
+    Combines the list 8 at a time, treating each group of 8 bits
+    as a single byte.
+
+    Args:
+        bit_list (Sequence): Sequence of 1s and 0s.
+
+    Returns:
+        bytes: The decoded bytes.
+    """
+    num_bits = len(bit_list)
+    byte_vals = bytearray()
+    for start in six.moves.xrange(0, num_bits, 8):
+        curr_bits = bit_list[start:start + 8]
+        char_val = sum(val * digit
+                       for val, digit in six.moves.zip(_POW2, curr_bits))
+        byte_vals.append(char_val)
+    return bytes(byte_vals)
+
+
+class Verifier(object):
+    """This object is used to verify cryptographic signatures.
+
+    Args:
+        public_key (rsa.key.PublicKey): The public key used to verify
+            signatures.
+    """
+
+    def __init__(self, public_key):
+        self._pubkey = public_key
+
+    def verify(self, message, signature):
+        """Verifies a message against a cryptographic signature.
+
+        Args:
+            message (Union[str, bytes]): The message to verify.
+            signature (Union[str, bytes]): The cryptography signature to check.
+
+        Returns:
+            bool: True if message was signed by the private key associated
+            with the public key that this object was constructed with.
+        """
+        message = _helpers.to_bytes(message)
+        try:
+            return rsa.pkcs1.verify(message, signature, self._pubkey)
+        except (ValueError, rsa.pkcs1.VerificationError):
+            return False
+
+    @classmethod
+    def from_string(cls, public_key):
+        """Construct an Verifier instance from a public key or public
+        certificate string.
+
+        Args:
+            public_key (Union[str, bytes]): The public key in PEM format or the
+                x509 public key certificate.
+
+        Returns:
+            Verifier: The constructed verifier.
+
+        Raises:
+            ValueError: If the public_key can't be parsed.
+        """
+        public_key = _helpers.to_bytes(public_key)
+        is_x509_cert = _CERTIFICATE_MARKER in public_key
+
+        # If this is a certificate, extract the public key info.
+        if is_x509_cert:
+            der = rsa.pem.load_pem(public_key, 'CERTIFICATE')
+            asn1_cert, remaining = decoder.decode(der, asn1Spec=Certificate())
+            if remaining != b'':
+                raise ValueError('Unused bytes', remaining)
+
+            cert_info = asn1_cert['tbsCertificate']['subjectPublicKeyInfo']
+            key_bytes = _bit_list_to_bytes(cert_info['subjectPublicKey'])
+            pubkey = rsa.PublicKey.load_pkcs1(key_bytes, 'DER')
+        else:
+            pubkey = rsa.PublicKey.load_pkcs1(public_key, 'PEM')
+        return cls(pubkey)
+
+
+def verify_signature(message, signature, certs):
+    """Verify a cryptographic signature.
+
+    Checks that the provided ``signature`` was generated from ``bytes`` using
+    the private key associated with the ``cert``.
+
+    Args:
+        message (Union[str, bytes]): The plaintext message.
+        signature (Union[str, bytes]): The cryptographic signature to check.
+        certs (Union[Sequence, str, bytes]): The certificate or certificates
+            to use to check the signature.
+
+    Returns:
+        bool: True if the signature is valid, otherwise False.
+    """
+    if isinstance(certs, (six.text_type, six.binary_type)):
+        certs = [certs]
+
+    for cert in certs:
+        verifier = Verifier.from_string(cert)
+        if verifier.verify(message, signature):
+            return True
+    return False
+
+
+class Signer(object):
+    """Signs messages with a private key.
+
+    Args:
+        private_key (rsa.key.PrivateKey): The private key to sign with.
+        key_id (str): Optional key ID used to identify this private key. This
+            can be useful to associate the private key with its associated
+            public key or certificate.
+    """
+
+    def __init__(self, private_key, key_id=None):
+        self._key = private_key
+        self.key_id = key_id
+
+    def sign(self, message):
+        """Signs a message.
+
+        Args:
+            message (Union[str, bytes]): The message to be signed.
+
+        Returns:
+            bytes: The signature of the message for the given key.
+        """
+        message = _helpers.to_bytes(message)
+        return rsa.pkcs1.sign(message, self._key, 'SHA-256')
+
+    @classmethod
+    def from_string(cls, key, key_id=None):
+        """Construct an Signer instance from a private key in PEM format.
+
+        Args:
+            key (str): Private key in PEM format.
+            key_id (str): An optional key id used to identify the private key.
+
+        Returns:
+            Signer: The constructed signer.
+
+        Raises:
+            ValueError: If the key cannot be parsed as PKCS#1 or PKCS#8 in
+                PEM format.
+        """
+        key = _helpers.from_bytes(key)  # PEM expects str in Python 3
+        marker_id, key_bytes = pem.readPemBlocksFromFile(
+            six.StringIO(key), _PKCS1_MARKER, _PKCS8_MARKER)
+
+        # Key is in pkcs1 format.
+        if marker_id == 0:
+            private_key = rsa.key.PrivateKey.load_pkcs1(
+                key_bytes, format='DER')
+        # Key is in pkcs8.
+        elif marker_id == 1:
+            key_info, remaining = decoder.decode(
+                key_bytes, asn1Spec=_PKCS8_SPEC)
+            if remaining != b'':
+                raise ValueError('Unused bytes', remaining)
+            private_key_info = key_info.getComponentByName('privateKey')
+            private_key = rsa.key.PrivateKey.load_pkcs1(
+                private_key_info.asOctets(), format='DER')
+        else:
+            raise ValueError('No key could be detected.')
+
+        return cls(private_key, key_id=key_id)
diff --git a/tests/data/other_cert.pem b/tests/data/other_cert.pem
new file mode 100644
index 0000000..6895d1e
--- /dev/null
+++ b/tests/data/other_cert.pem
@@ -0,0 +1,33 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/data/pem_from_pkcs12.pem b/tests/data/pem_from_pkcs12.pem
new file mode 100644
index 0000000..2d77e10
--- /dev/null
+++ b/tests/data/pem_from_pkcs12.pem
@@ -0,0 +1,32 @@
+Bag Attributes
+    friendlyName: key
+    localKeyID: 22 7E 04 FC 64 48 20 83 1E C1 BD E3 F5 2F 44 7D EA 99 A5 BC 
+Key Attributes: <No Attributes>
+-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----
diff --git a/tests/data/privatekey.p12 b/tests/data/privatekey.p12
new file mode 100644
index 0000000..c369ecb
--- /dev/null
+++ b/tests/data/privatekey.p12
Binary files differ
diff --git a/tests/data/privatekey.pem b/tests/data/privatekey.pem
new file mode 100644
index 0000000..5744354
--- /dev/null
+++ b/tests/data/privatekey.pem
@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----
diff --git a/tests/data/privatekey.pub b/tests/data/privatekey.pub
new file mode 100644
index 0000000..11fdaa4
--- /dev/null
+++ b/tests/data/privatekey.pub
@@ -0,0 +1,8 @@
+-----BEGIN RSA PUBLIC KEY-----
+MIIBCgKCAQEA4ej0p7bQ7L/r4rVGUz9RN4VQWoej1Bg1mYWIDYslvKrk1gpj7wZg
+kdmM7oVK2OfgrSj/FCTkInKPqaCR0gD7K80q+mLBrN3PUkDrJQZpvRZIff3/xmVU
+1WeruQLFJjnFb2dqu0s/FY/2kWiJtBCakXvXEOb7zfbINuayL+MSsCGSdVYsSliS
+5qQpgyDap+8b5fpXZVJkq92hrcNtbkg7hCYUJczt8n9hcCTJCfUpApvaFQ18pe+z
+pyl4+WzkP66I28hniMQyUlA1hBiskT7qiouq0m8IOodhv2fagSZKjOTTU2xkSBc/
+/fy3ZpsL7WqgsZS7Q+0VRK8gKfqkxg5OYQIDAQAB
+-----END RSA PUBLIC KEY-----
diff --git a/tests/data/public_cert.pem b/tests/data/public_cert.pem
new file mode 100644
index 0000000..7af6ca3
--- /dev/null
+++ b/tests/data/public_cert.pem
@@ -0,0 +1,19 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
diff --git a/tests/test__helpers.py b/tests/test__helpers.py
new file mode 100644
index 0000000..b7e0bab
--- /dev/null
+++ b/tests/test__helpers.py
@@ -0,0 +1,50 @@
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import pytest
+
+from google.auth import _helpers
+
+
+def test_to_bytes_with_bytes():
+    value = b'bytes-val'
+    assert _helpers.to_bytes(value) == value
+
+
+def test_to_bytes_with_unicode():
+    value = u'string-val'
+    encoded_value = b'string-val'
+    assert _helpers.to_bytes(value) == encoded_value
+
+
+def test_to_bytes_with_nonstring_type():
+    with pytest.raises(ValueError):
+        _helpers.to_bytes(object())
+
+
+def test_from_bytes_with_unicode():
+    value = u'bytes-val'
+    assert _helpers.from_bytes(value) == value
+
+
+def test_from_bytes_with_bytes():
+    value = b'string-val'
+    decoded_value = u'string-val'
+    assert _helpers.from_bytes(value) == decoded_value
+
+
+def test_from_bytes_with_nonstring_type():
+    with pytest.raises(ValueError):
+        _helpers.from_bytes(object())
diff --git a/tests/test_crypt.py b/tests/test_crypt.py
new file mode 100644
index 0000000..9069216
--- /dev/null
+++ b/tests/test_crypt.py
@@ -0,0 +1,186 @@
+# Copyright 2016 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+
+import mock
+from pyasn1_modules import pem
+import pytest
+import rsa
+import six
+
+from google.auth import _helpers
+from google.auth import crypt
+
+
+DATA_DIR = os.path.join(os.path.dirname(__file__), 'data')
+
+# To generate privatekey.pem, privatekey.pub, and public_cert.pem:
+#   $ openssl req -new -newkey rsa:1024 -x509 -nodes -out public_cert.pem \
+#   >    -keyout privatekey.pem
+#   $ openssl rsa -in privatekey.pem -pubout -out privatekey.pub
+
+with open(os.path.join(DATA_DIR, 'privatekey.pem'), 'rb') as fh:
+    PRIVATE_KEY_BYTES = fh.read()
+    PKCS1_KEY_BYTES = PRIVATE_KEY_BYTES
+
+with open(os.path.join(DATA_DIR, 'privatekey.pub'), 'rb') as fh:
+    PUBLIC_KEY_BYTES = fh.read()
+
+with open(os.path.join(DATA_DIR, 'public_cert.pem'), 'rb') as fh:
+    PUBLIC_CERT_BYTES = fh.read()
+
+# To generate other_cert.pem:
+#   $ openssl req -new -newkey rsa:1024 -x509 -nodes -out other_cert.pem
+
+with open(os.path.join(DATA_DIR, 'other_cert.pem'), 'rb') as fh:
+    OTHER_CERT_BYTES = fh.read()
+
+# To generate pem_from_pkcs12.pem and privatekey.p12:
+#   $ openssl pkcs12 -export -out privatekey.p12 -inkey privatekey.pem \
+#   >    -in public_cert.pem
+#   $ openssl pkcs12 -in privatekey.p12 -nocerts -nodes \
+#   >   -out pem_from_pkcs12.pem
+
+with open(os.path.join(DATA_DIR, 'pem_from_pkcs12.pem'), 'rb') as fh:
+    PKCS8_KEY_BYTES = fh.read()
+
+with open(os.path.join(DATA_DIR, 'privatekey.p12'), 'rb') as fh:
+    PKCS12_KEY_BYTES = fh.read()
+
+
+def test_verify_signature():
+    to_sign = b'foo'
+    signer = crypt.Signer.from_string(PRIVATE_KEY_BYTES)
+    signature = signer.sign(to_sign)
+
+    assert crypt.verify_signature(
+        to_sign, signature, PUBLIC_CERT_BYTES)
+
+    # List of certs
+    assert crypt.verify_signature(
+        to_sign, signature, [OTHER_CERT_BYTES, PUBLIC_CERT_BYTES])
+
+
+def test_verify_signature_failure():
+    to_sign = b'foo'
+    signer = crypt.Signer.from_string(PRIVATE_KEY_BYTES)
+    signature = signer.sign(to_sign)
+
+    assert not crypt.verify_signature(
+        to_sign, signature, OTHER_CERT_BYTES)
+
+
+class TestVerifier(object):
+    def test_verify_success(self):
+        to_sign = b'foo'
+        signer = crypt.Signer.from_string(PRIVATE_KEY_BYTES)
+        actual_signature = signer.sign(to_sign)
+
+        verifier = crypt.Verifier.from_string(PUBLIC_KEY_BYTES)
+        assert verifier.verify(to_sign, actual_signature)
+
+    def test_verify_unicode_success(self):
+        to_sign = u'foo'
+        signer = crypt.Signer.from_string(PRIVATE_KEY_BYTES)
+        actual_signature = signer.sign(to_sign)
+
+        verifier = crypt.Verifier.from_string(PUBLIC_KEY_BYTES)
+        assert verifier.verify(to_sign, actual_signature)
+
+    def test_verify_failure(self):
+        verifier = crypt.Verifier.from_string(PUBLIC_KEY_BYTES)
+        bad_signature1 = b''
+        assert not verifier.verify(b'foo', bad_signature1)
+        bad_signature2 = b'a'
+        assert not verifier.verify(b'foo', bad_signature2)
+
+    def test_from_string_pub_key(self):
+        verifier = crypt.Verifier.from_string(PUBLIC_KEY_BYTES)
+        assert isinstance(verifier, crypt.Verifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_key_unicode(self):
+        public_key = _helpers.from_bytes(PUBLIC_KEY_BYTES)
+        verifier = crypt.Verifier.from_string(public_key)
+        assert isinstance(verifier, crypt.Verifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_cert(self):
+        verifier = crypt.Verifier.from_string(PUBLIC_CERT_BYTES)
+        assert isinstance(verifier, crypt.Verifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_cert_unicode(self):
+        public_cert = _helpers.from_bytes(PUBLIC_CERT_BYTES)
+        verifier = crypt.Verifier.from_string(public_cert)
+        assert isinstance(verifier, crypt.Verifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_cert_failure(self):
+        cert_bytes = PUBLIC_CERT_BYTES
+        true_der = rsa.pem.load_pem(cert_bytes, 'CERTIFICATE')
+        with mock.patch('rsa.pem.load_pem',
+                        return_value=true_der + b'extra') as load_pem:
+            with pytest.raises(ValueError):
+                crypt.Verifier.from_string(cert_bytes)
+            load_pem.assert_called_once_with(cert_bytes, 'CERTIFICATE')
+
+
+class TestSigner(object):
+    def test_from_string_pkcs1(self):
+        signer = crypt.Signer.from_string(PKCS1_KEY_BYTES)
+        assert isinstance(signer, crypt.Signer)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs1_unicode(self):
+        key_bytes = _helpers.from_bytes(PKCS1_KEY_BYTES)
+        signer = crypt.Signer.from_string(key_bytes)
+        assert isinstance(signer, crypt.Signer)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs8(self):
+        signer = crypt.Signer.from_string(PKCS8_KEY_BYTES)
+        assert isinstance(signer, crypt.Signer)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs8_extra_bytes(self):
+        key_bytes = PKCS8_KEY_BYTES
+        _, pem_bytes = pem.readPemBlocksFromFile(
+            six.StringIO(_helpers.from_bytes(key_bytes)),
+            crypt._PKCS8_MARKER)
+
+        with mock.patch('pyasn1.codec.der.decoder.decode') as mock_decode:
+            key_info, remaining = None, 'extra'
+            mock_decode.return_value = (key_info, remaining)
+            with pytest.raises(ValueError):
+                crypt.Signer.from_string(key_bytes)
+            # Verify mock was called.
+            mock_decode.assert_called_once_with(
+                pem_bytes, asn1Spec=crypt._PKCS8_SPEC)
+
+    def test_from_string_pkcs8_unicode(self):
+        key_bytes = _helpers.from_bytes(PKCS8_KEY_BYTES)
+        signer = crypt.Signer.from_string(key_bytes)
+        assert isinstance(signer, crypt.Signer)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs12(self):
+        with pytest.raises(ValueError):
+            crypt.Signer.from_string(PKCS12_KEY_BYTES)
+
+    def test_from_string_bogus_key(self):
+        key_bytes = 'bogus-key'
+        with pytest.raises(ValueError):
+            crypt.Signer.from_string(key_bytes)
diff --git a/tox.ini b/tox.ini
index d2a5f1f..5f2df1c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,7 +25,9 @@
 deps =
   {[testenv]deps}
   sphinx
-commands = sphinx-apidoc --output-dir docs/reference --separate --module-first google
+commands =
+  rm -r docs/reference
+  sphinx-apidoc --output-dir docs/reference --separate --module-first google
 
 [testenv:docs]
 basepython = python3.5