diff --git a/tests/crypt/__init__.py b/tests/crypt/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/crypt/__init__.py
diff --git a/tests/crypt/test__python_rsa.py b/tests/crypt/test__python_rsa.py
new file mode 100644
index 0000000..cff1034
--- /dev/null
+++ b/tests/crypt/test__python_rsa.py
@@ -0,0 +1,194 @@
+# 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 json
+import os
+
+import mock
+from pyasn1_modules import pem
+import pytest
+import rsa
+import six
+
+from google.auth import _helpers
+from google.auth.crypt import _python_rsa
+
+
+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 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()
+
+# The service account JSON file can be generated from the Google Cloud Console.
+SERVICE_ACCOUNT_JSON_FILE = os.path.join(DATA_DIR, 'service_account.json')
+
+with open(SERVICE_ACCOUNT_JSON_FILE, 'r') as fh:
+    SERVICE_ACCOUNT_INFO = json.load(fh)
+
+
+class TestRSAVerifier(object):
+    def test_verify_success(self):
+        to_sign = b'foo'
+        signer = _python_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
+        actual_signature = signer.sign(to_sign)
+
+        verifier = _python_rsa.RSAVerifier.from_string(PUBLIC_KEY_BYTES)
+        assert verifier.verify(to_sign, actual_signature)
+
+    def test_verify_unicode_success(self):
+        to_sign = u'foo'
+        signer = _python_rsa.RSASigner.from_string(PRIVATE_KEY_BYTES)
+        actual_signature = signer.sign(to_sign)
+
+        verifier = _python_rsa.RSAVerifier.from_string(PUBLIC_KEY_BYTES)
+        assert verifier.verify(to_sign, actual_signature)
+
+    def test_verify_failure(self):
+        verifier = _python_rsa.RSAVerifier.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 = _python_rsa.RSAVerifier.from_string(PUBLIC_KEY_BYTES)
+        assert isinstance(verifier, _python_rsa.RSAVerifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_key_unicode(self):
+        public_key = _helpers.from_bytes(PUBLIC_KEY_BYTES)
+        verifier = _python_rsa.RSAVerifier.from_string(public_key)
+        assert isinstance(verifier, _python_rsa.RSAVerifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_cert(self):
+        verifier = _python_rsa.RSAVerifier.from_string(PUBLIC_CERT_BYTES)
+        assert isinstance(verifier, _python_rsa.RSAVerifier)
+        assert isinstance(verifier._pubkey, rsa.key.PublicKey)
+
+    def test_from_string_pub_cert_unicode(self):
+        public_cert = _helpers.from_bytes(PUBLIC_CERT_BYTES)
+        verifier = _python_rsa.RSAVerifier.from_string(public_cert)
+        assert isinstance(verifier, _python_rsa.RSAVerifier)
+        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')
+        load_pem_patch = mock.patch(
+            'rsa.pem.load_pem', return_value=true_der + b'extra',
+            autospec=True)
+
+        with load_pem_patch as load_pem:
+            with pytest.raises(ValueError):
+                _python_rsa.RSAVerifier.from_string(cert_bytes)
+            load_pem.assert_called_once_with(cert_bytes, 'CERTIFICATE')
+
+
+class TestRSASigner(object):
+    def test_from_string_pkcs1(self):
+        signer = _python_rsa.RSASigner.from_string(PKCS1_KEY_BYTES)
+        assert isinstance(signer, _python_rsa.RSASigner)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs1_unicode(self):
+        key_bytes = _helpers.from_bytes(PKCS1_KEY_BYTES)
+        signer = _python_rsa.RSASigner.from_string(key_bytes)
+        assert isinstance(signer, _python_rsa.RSASigner)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs8(self):
+        signer = _python_rsa.RSASigner.from_string(PKCS8_KEY_BYTES)
+        assert isinstance(signer, _python_rsa.RSASigner)
+        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)),
+            _python_rsa._PKCS8_MARKER)
+
+        key_info, remaining = None, 'extra'
+        decode_patch = mock.patch(
+            'pyasn1.codec.der.decoder.decode',
+            return_value=(key_info, remaining),
+            autospec=True)
+
+        with decode_patch as decode:
+            with pytest.raises(ValueError):
+                _python_rsa.RSASigner.from_string(key_bytes)
+            # Verify mock was called.
+            decode.assert_called_once_with(
+                pem_bytes, asn1Spec=_python_rsa._PKCS8_SPEC)
+
+    def test_from_string_pkcs8_unicode(self):
+        key_bytes = _helpers.from_bytes(PKCS8_KEY_BYTES)
+        signer = _python_rsa.RSASigner.from_string(key_bytes)
+        assert isinstance(signer, _python_rsa.RSASigner)
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_string_pkcs12(self):
+        with pytest.raises(ValueError):
+            _python_rsa.RSASigner.from_string(PKCS12_KEY_BYTES)
+
+    def test_from_string_bogus_key(self):
+        key_bytes = 'bogus-key'
+        with pytest.raises(ValueError):
+            _python_rsa.RSASigner.from_string(key_bytes)
+
+    def test_from_service_account_info(self):
+        signer = _python_rsa.RSASigner.from_service_account_info(
+            SERVICE_ACCOUNT_INFO)
+
+        assert signer.key_id == SERVICE_ACCOUNT_INFO[
+            _python_rsa._JSON_FILE_PRIVATE_KEY_ID]
+        assert isinstance(signer._key, rsa.key.PrivateKey)
+
+    def test_from_service_account_info_missing_key(self):
+        with pytest.raises(ValueError) as excinfo:
+            _python_rsa.RSASigner.from_service_account_info({})
+
+        assert excinfo.match(_python_rsa._JSON_FILE_PRIVATE_KEY)
+
+    def test_from_service_account_file(self):
+        signer = _python_rsa.RSASigner.from_service_account_file(
+            SERVICE_ACCOUNT_JSON_FILE)
+
+        assert signer.key_id == SERVICE_ACCOUNT_INFO[
+            _python_rsa._JSON_FILE_PRIVATE_KEY_ID]
+        assert isinstance(signer._key, rsa.key.PrivateKey)
diff --git a/tests/crypt/test_crypt.py b/tests/crypt/test_crypt.py
new file mode 100644
index 0000000..d8b1d00
--- /dev/null
+++ b/tests/crypt/test_crypt.py
@@ -0,0 +1,59 @@
+# 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
+
+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()
+
+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()
+
+
+def test_verify_signature():
+    to_sign = b'foo'
+    signer = crypt.RSASigner.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.RSASigner.from_string(PRIVATE_KEY_BYTES)
+    signature = signer.sign(to_sign)
+
+    assert not crypt.verify_signature(
+        to_sign, signature, OTHER_CERT_BYTES)