feat: add ecdsa p-384 support (#1872)

GDC (Google Distributed Cloud) needs to support ECDSA-P384 keys for
compliance. This change creates an EsSigner and EsVerifier class that is
capable of supporting both ECDSA-P256 and ECDSA-P384 keys for backwards
compatibility. The EsSigner and EsVerifier classes are plumbed through
to the GDC service accounts and are used to both sign and verify JWTs.

This implementation was successfully tested against a GDC instance using
both ECDSA-P256 and ECDSA-P384 keys.

---------

Co-authored-by: Daniel Sanche <d.sanche14@gmail.com>

Author: shengjiang3

google/auth/_service_account_info.py

@@ -56,7 +56,7 @@ def from_dict(data, require=None, use_rsa_signer=True):
     if use_rsa_signer:
         signer = crypt.RSASigner.from_service_account_info(data)
     else:
-        signer = crypt.ES256Signer.from_service_account_info(data)
+        signer = crypt.EsSigner.from_service_account_info(data)
 
     return signer
 

google/auth/crypt/__init__.py

@@ -40,20 +40,31 @@
 from google.auth.crypt import base
 from google.auth.crypt import rsa
 
+# google.auth.crypt.es depends on the crytpography module which may not be
+# successfully imported depending on the system.
 try:
+    from google.auth.crypt import es
     from google.auth.crypt import es256
 except ImportError:  # pragma: NO COVER
+    es = None  # type: ignore
     es256 = None  # type: ignore
 
-if es256 is not None:  # pragma: NO COVER
+if es is not None and es256 is not None:  # pragma: NO COVER
     __all__ = [
+        "EsSigner",
+        "EsVerifier",
         "ES256Signer",
         "ES256Verifier",
         "RSASigner",
         "RSAVerifier",
         "Signer",
         "Verifier",
     ]
+
+    EsSigner = es.EsSigner
+    EsVerifier = es.EsVerifier
+    ES256Signer = es256.ES256Signer
+    ES256Verifier = es256.ES256Verifier
 else:  # pragma: NO COVER
     __all__ = ["RSASigner", "RSAVerifier", "Signer", "Verifier"]
 
@@ -65,10 +76,6 @@
 RSASigner = rsa.RSASigner
 RSAVerifier = rsa.RSAVerifier
 
-if es256 is not None:  # pragma: NO COVER
-    ES256Signer = es256.ES256Signer
-    ES256Verifier = es256.ES256Verifier
-
 
 def verify_signature(message, signature, certs, verifier_cls=rsa.RSAVerifier):
     """Verify an RSA or ECDSA cryptographic signature.

google/auth/crypt/es.py

@@ -0,0 +1,221 @@
+# Copyright 2017 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.
+
+"""ECDSA verifier and signer that use the ``cryptography`` library.
+"""
+
+from dataclasses import dataclass
+from typing import Any, Dict, Optional, Union
+
+import cryptography.exceptions
+from cryptography.hazmat import backends
+from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives import serialization
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives.asymmetric import padding
+from cryptography.hazmat.primitives.asymmetric.utils import decode_dss_signature
+from cryptography.hazmat.primitives.asymmetric.utils import encode_dss_signature
+import cryptography.x509
+
+from google.auth import _helpers
+from google.auth.crypt import base
+
+
+_CERTIFICATE_MARKER = b"-----BEGIN CERTIFICATE-----"
+_BACKEND = backends.default_backend()
+_PADDING = padding.PKCS1v15()
+
+
+@dataclass
+class _ESAttributes:
+    """A class that models ECDSA attributes.
+
+    Attributes:
+        rs_size (int): Size for ASN.1 r and s size.
+        sha_algo (hashes.HashAlgorithm): Hash algorithm.
+        algorithm (str): Algorithm name.
+    """
+
+    rs_size: int
+    sha_algo: hashes.HashAlgorithm
+    algorithm: str
+
+    @classmethod
+    def from_key(
+        cls, key: Union[ec.EllipticCurvePublicKey, ec.EllipticCurvePrivateKey]
+    ):
+        return cls.from_curve(key.curve)
+
+    @classmethod
+    def from_curve(cls, curve: ec.EllipticCurve):
+        # ECDSA raw signature has (r||s) format where r,s are two
+        # integers of size 32 bytes for P-256 curve and 48 bytes
+        # for P-384 curve. For P-256 curve, we use SHA256 hash algo,
+        # and for P-384 curve we use SHA384 algo.
+        if isinstance(curve, ec.SECP384R1):
+            return cls(48, hashes.SHA384(), "ES384")
+        else:
+            # default to ES256
+            return cls(32, hashes.SHA256(), "ES256")
+
+
+class EsVerifier(base.Verifier):
+    """Verifies ECDSA cryptographic signatures using public keys.
+
+    Args:
+        public_key (
+                cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePublicKey):
+            The public key used to verify signatures.
+    """
+
+    def __init__(self, public_key: ec.EllipticCurvePublicKey) -> None:
+        self._pubkey = public_key
+        self._attributes = _ESAttributes.from_key(public_key)
+
+    @_helpers.copy_docstring(base.Verifier)
+    def verify(self, message: bytes, signature: bytes) -> bool:
+        # First convert (r||s) raw signature to ASN1 encoded signature.
+        sig_bytes = _helpers.to_bytes(signature)
+        if len(sig_bytes) != self._attributes.rs_size * 2:
+            return False
+        r = int.from_bytes(sig_bytes[: self._attributes.rs_size], byteorder="big")
+        s = int.from_bytes(sig_bytes[self._attributes.rs_size :], byteorder="big")
+        asn1_sig = encode_dss_signature(r, s)
+
+        message = _helpers.to_bytes(message)
+        try:
+            self._pubkey.verify(asn1_sig, message, ec.ECDSA(self._attributes.sha_algo))
+            return True
+        except (ValueError, cryptography.exceptions.InvalidSignature):
+            return False
+
+    @classmethod
+    def from_string(cls, public_key: Union[str, bytes]) -> "EsVerifier":
+        """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_data = _helpers.to_bytes(public_key)
+
+        if _CERTIFICATE_MARKER in public_key_data:
+            cert = cryptography.x509.load_pem_x509_certificate(
+                public_key_data, _BACKEND
+            )
+            pubkey = cert.public_key()  # type: Any
+
+        else:
+            pubkey = serialization.load_pem_public_key(public_key_data, _BACKEND)
+
+        if not isinstance(pubkey, ec.EllipticCurvePublicKey):
+            raise TypeError("Expected public key of type EllipticCurvePublicKey")
+
+        return cls(pubkey)
+
+
+class EsSigner(base.Signer, base.FromServiceAccountMixin):
+    """Signs messages with an ECDSA private key.
+
+    Args:
+        private_key (
+                cryptography.hazmat.primitives.asymmetric.ec.EllipticCurvePrivateKey):
+            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: ec.EllipticCurvePrivateKey, key_id: Optional[str] = None
+    ) -> None:
+        self._key = private_key
+        self._key_id = key_id
+        self._attributes = _ESAttributes.from_key(private_key)
+
+    @property
+    def algorithm(self) -> str:
+        """Name of the algorithm used to sign messages.
+        Returns:
+            str: The algorithm name.
+        """
+        return self._attributes.algorithm
+
+    @property  # type: ignore
+    @_helpers.copy_docstring(base.Signer)
+    def key_id(self) -> Optional[str]:
+        return self._key_id
+
+    @_helpers.copy_docstring(base.Signer)
+    def sign(self, message: bytes) -> bytes:
+        message = _helpers.to_bytes(message)
+        asn1_signature = self._key.sign(message, ec.ECDSA(self._attributes.sha_algo))
+
+        # Convert ASN1 encoded signature to (r||s) raw signature.
+        (r, s) = decode_dss_signature(asn1_signature)
+        return r.to_bytes(self._attributes.rs_size, byteorder="big") + s.to_bytes(
+            self._attributes.rs_size, byteorder="big"
+        )
+
+    @classmethod
+    def from_string(
+        cls, key: Union[bytes, str], key_id: Optional[str] = None
+    ) -> "EsSigner":
+        """Construct a RSASigner from a private key in PEM format.
+
+        Args:
+            key (Union[bytes, str]): Private key in PEM format.
+            key_id (str): An optional key id used to identify the private key.
+
+        Returns:
+            google.auth.crypt._cryptography_rsa.RSASigner: The
+            constructed signer.
+
+        Raises:
+            ValueError: If ``key`` is not ``bytes`` or ``str`` (unicode).
+            UnicodeDecodeError: If ``key`` is ``bytes`` but cannot be decoded
+                into a UTF-8 ``str``.
+            ValueError: If ``cryptography`` "Could not deserialize key data."
+        """
+        key_bytes = _helpers.to_bytes(key)
+        private_key = serialization.load_pem_private_key(
+            key_bytes, password=None, backend=_BACKEND
+        )
+
+        if not isinstance(private_key, ec.EllipticCurvePrivateKey):
+            raise TypeError("Expected private key of type EllipticCurvePrivateKey")
+
+        return cls(private_key, key_id=key_id)
+
+    def __getstate__(self) -> Dict[str, Any]:
+        """Pickle helper that serializes the _key attribute."""
+        state = self.__dict__.copy()
+        state["_key"] = self._key.private_bytes(
+            encoding=serialization.Encoding.PEM,
+            format=serialization.PrivateFormat.PKCS8,
+            encryption_algorithm=serialization.NoEncryption(),
+        )
+        return state
+
+    def __setstate__(self, state: Dict[str, Any]) -> None:
+        """Pickle helper that deserializes the _key attribute."""
+        state["_key"] = serialization.load_pem_private_key(state["_key"], None)
+        self.__dict__.update(state)