Add kms/attestations/ directory with sample script to verify attestations

kms/attestations/README.rst.in

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+# This file is used to generate README.rst
+
+product:
+  name: Google Cloud Key Management Service
+  short_name: Cloud Key Management Service
+  url: https://cloud.google.com/kms/docs/
+  description: >
+    The `Cloud Key Management Service`_ allows you to create, import, and manage
+    cryptographic keys and perform cryptographic operations in a single centralized cloud service.
+
+setup:
+- install_deps
+
+samples:
+- name: Verify attestations for keys generated by Cloud HSM
+  file: verify_attestation.py
+  show_help: True
+
+folder: kms/attestations

kms/attestations/requirements-test.txt

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+pytest==5.3.2

kms/attestations/requirements.txt

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+cryptography==2.8
+pem==20.1.0

kms/attestations/verify_attestation.py

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+#!/usr/bin/env python
+
+# Copyright 2020 Google, LLC.
+#
+# 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.
+
+"""This sample demonstrates how to verify HSM attestations using certificate
+bundles obtained from Cloud HSM.
+
+For more information, visit https://cloud.google.com/kms/docs/attest-key.
+"""
+
+# [START verify_attestations]
+import gzip
+
+from cryptography import exceptions
+from cryptography import x509
+from cryptography.hazmat import backends
+from cryptography.hazmat.primitives.asymmetric import padding
+import pem
+
+
+def verify(attestation_file, bundle_file):
+    """Verifies an attestation using a bundle of certificates.
+
+    Args:
+      attestation_file: The name of the attestation file.
+      bundle_file: The name of the bundle file containing the certificates
+        used to verify the attestation.
+
+    Returns:
+      True if at least one of the certificates in bundle_file can verify the
+      attestation data and its signature.
+    """
+    with gzip.open(attestation_file, 'rb') as f:
+        # An attestation file consists of a data portion and a 256 byte
+        # signature portion concatenated together.
+        attestation = f.read()
+        # Separate the components.
+        data = attestation[:-256]
+        signature = attestation[-256:]
+
+        # Verify the attestation with one of the certificates in the bundle
+        for cert in pem.parse_file(bundle_file):
+            cert_obj = x509.load_pem_x509_certificate(
+                str(cert).encode('utf-8'), backends.default_backend())
+            try:
+                # Check if the data was signed by the private key assosicated
+                # with the public key in the certificate. The data should have
+                # been signed with PKCS1v15 padding.
+                cert_obj.public_key().verify(
+                    signature, data, padding.PKCS1v15(),
+                    cert_obj.signature_hash_algorithm)
+                return True
+            except exceptions.InvalidSignature:
+                # Certificate bundles contain certificates that will not be
+                # able to verify the attestation, so the InvalidSignature
+                # errors can be ignored.
+                continue
+        return False
+# [END verify_attestations]

kms/attestations/verify_attestation_test.py

@@ -0,0 +1,109 @@
+# Copyright 2020 Google, LLC.
+#
+# 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 tempfile
+
+import verify_attestation
+
+# Test certificate bundles can be generated with the following steps:
+# 1. Generate test key pairs.
+#    - openssl genrsa -out test1.key 2048
+#    - openssl genrsa -out test2.key 2048
+# 2. Generate test certificates using the key pairs.
+#    - openssl req -x509 -key test1.key -days 3650 -out test1.pem
+#    - openssl req -x509 -key test2.key -days 3650 -out test2.pem
+# 3. Create a bundle using the test certificates.
+#    - cat test1.pem test2.pem > bundle.pem
+# For instructions on downloading certificate bundles from Cloud HSM, refer to:
+# https://cloud.google.com/kms/docs/attest-key#downloading_the_certificates
+TEST_CERT_BUNDLE = b"""-----BEGIN CERTIFICATE-----
+MIIDZDCCAkwCFE2PSNf++wMw+Jv86m41lbsa9aUMMA0GCSqGSIb3DQEBCwUAMFkx
+CzAJBgNVBAYTAkFVMRMwEQYDVQQIDApTb21lLVN0YXRlMSEwHwYDVQQKDBhJbnRl
+cm5ldCBXaWRnaXRzIFB0eSBMdGQxEjAQBgNVBAMMCVRlc3QgQ2FyZDAeFw0yMDAz
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+0UaAcqt8+QM=
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----
+MIIDRjCCAi4CFBVm+eV+oRkaYq2NyuTfwxWapjFOMA0GCSqGSIb3DQEBCwUAMGYx
+CzAJBgNVBAYTAkFVMRMwEQYDVQQIDApTb21lLVN0YXRlMSEwHwYDVQQKDBhJbnRl
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+biaxW9fnsJIXirAE03FFkC/tWelkGFkmMfs=
+-----END CERTIFICATE-----"""
+
+# Test attestations can be generated with the following steps:
+# 1. Create a file containing the test attestation statement.
+#    - echo "content" > attestation.dat
+# 2. Sign the file with one the key pairs used to create the test certificates.
+#    - openssl dgst -sha256 -sign test1.key -out signature.dat attestation.dat
+# 3. Concatenate the signature to the statement to create an attestation.
+#    - cat signature.dat >> attestation.dat
+# 4. Compress the test attestation.
+#    - gzip attestation.dat
+# For instructions on downloading attestations from Cloud HSM, refer to:
+# https://cloud.google.com/kms/docs/attest-key#downloading_the_attestation_statement
+TEST_ATTESTATION_GZ = (
+    b'\x1f\x8b\x08\x08\xda\xde\x84^\x00\x03attestation\x00\x01\x06\x01\xf9\xfe'
+    b'\x15\xa7~W\xdazHq03\x95\xd1F\xcf\x1d\n\xe0\xbbv\x11\xed\xae\x186\xc0\xcc'
+    b'.\xcf)\xf1?\xf7!\xf3\xd6M\x85\xfe\xb9\x84\xb2\x08V2(\xa1\x87]\xab\x01='
+    b'\xb5\x0f)~\x06\xee\xfa/\x94\xa6x\x96o\xb1\xcb$\x82\x90\xe03J\t\x03\xf0'
+    b'\xa4\xa5\xa9\xf9\xb2\xce\xdd2\xfam\x94W\x07\x00~\xa5\xc2\xcdq\xa1\x81'
+    b'\x18\x83\xe0\xd9\x11k]\xbd\xf8\x81@\x9c*\x80\x91R\xb0\xae\x9d\x88\xb8T'
+    b'\xd1>\xf6;\xe4\x83q%_\x8aw\x894\xb5:\xeab\xd2\x9a\x81\xdd\xa6\xf9\x94'
+    b'\xff8\xb1\xed\x7fs\x0e\xc0\xde\x89\x00]\x8fL\x82\x8a\x11\x8f\\\xe483\x9d'
+    b'&\x0b%\xfd\x0et\x8f\xa8\x1a\xb5K\xb4\xc7\x96\xd1}\x06\xdd\x93i\x1f\xc1@'
+    b'\x92\xef}(B\x0f\xd1\x03\xaaYo\x9b\xad\xa9zw#\xc8\x9a\xad\x94\xfc\x07q]x'
+    b'\xeb\xa2CA\xf8\xac\x96\xd9\xe5y4\xae]\x81\xb0$\x93\tx\xdb\xcc\x08:%\x1d'
+    b'\xe2q\xaa\xc8:\xc2<C\xb5\x9b\xd1\xb0<\x12\x8a\x99f\x11\x9a"Q\x1d]\xac'
+    b'\x81\xe2\x05\x06\x01\x00\x00')
+
+
+def test_verify():
+    with tempfile.NamedTemporaryFile() as attestation_file:
+        with tempfile.NamedTemporaryFile() as bundle_file:
+            attestation_file.write(TEST_ATTESTATION_GZ)
+            bundle_file.write(TEST_CERT_BUNDLE)
+
+            attestation_file.seek(0)
+            bundle_file.seek(0)
+
+            assert verify_attestation.verify(
+                attestation_file.name, bundle_file.name)