[python] Rewrite SGX signing in cryptography.io

Signed-off-by: Wojtek Porczyk <[email protected]>

python/graminelibos/sgx_sign.py

@@ -11,13 +11,12 @@
 import os
 import pathlib
 import struct
-import subprocess
 
 import click
 
 from cryptography.hazmat import backends
-from cryptography.hazmat.primitives import serialization
-from cryptography.hazmat.primitives.asymmetric import rsa
+from cryptography.hazmat.primitives import hashes, serialization
+from cryptography.hazmat.primitives.asymmetric import padding, rsa
 
 import elftools.elf.elffile
 
@@ -547,16 +546,41 @@ def get_tbssigstruct(manifest_path, date, libpal=SGX_LIBPAL, verbose=False):
 
 
 @click.command(add_help_option=False)
+@click.pass_context
 @click.help_option('--help-file')
 @click.option('--key', '-k', metavar='FILE',
-    type=click.Path(exists=True, dir_okay=False),
+    type=click.File('rb'),
     default=os.fspath(SGX_RSA_KEY_PATH),
     help='specify signing key (.pem) file')
-def sign_with_file(key):
-    return functools.partial(sign_with_local_key, key=key), [key]
+def sign_with_file(ctx, key):
+    try:
+        private_key = load_pem_private_key_from_file(key)
+    except InvalidRSAKeyError as e:
+        ctx.fail(str(e))
+
+    return functools.partial(sign_with_rsa_key, private_key=private_key), [key.name]
+
+
+class InvalidRSAKeyError(Exception):
+    pass
+
+
+def load_pem_private_key_from_file(file, passphrase=None):
+    with file:
+        private_key = serialization.load_pem_private_key(
+            file.read(), password=passphrase, backend=_cryptography_backend)
+
+    exponent = private_key.public_key().public_numbers().e
+
+    if exponent != SGX_RSA_PUBLIC_EXPONENT:
+        raise InvalidRSAKeyError(
+            f'invalid RSA key: expected exponent {SGX_RSA_PUBLIC_EXPONENT}, got {exponent}')
+
+    return private_key
+
 
 def sign_with_local_key(data, key):
-    """Signs *data* using *key*.
+    """Signs *data* using *key* loaded from file.
 
     Function used to generate an RSA signature over provided data using a 3072-bit private key with
     the public exponent of 3 (hard Intel SGX requirement on the key size and the exponent).
@@ -569,22 +593,32 @@ def sign_with_local_key(data, key):
     Returns:
         (int, int, int): Tuple of exponent, modulus and signature respectively.
     """
-    proc = subprocess.Popen(
-        ['openssl', 'rsa', '-modulus', '-in', key, '-noout'],
-        stdout=subprocess.PIPE)
-    modulus_out, _ = proc.communicate()
-    modulus = bytes.fromhex(modulus_out[8:8+offs.SE_KEY_SIZE*2].decode())
 
-    proc = subprocess.Popen(
-        ['openssl', 'sha256', '-binary', '-sign', key],
-        stdin=subprocess.PIPE, stdout=subprocess.PIPE)
-    signature, _ = proc.communicate(data)
+    with open(key, 'rb') as file:
+        private_key = load_pem_private_key_from_file(file)
 
-    exponent_int = 3
-    modulus_int = int.from_bytes(modulus, byteorder='big')
-    signature_int = int.from_bytes(signature, byteorder='big')
+    return sign_with_rsa_key(data, private_key)
 
-    return exponent_int, modulus_int, signature_int
+
+def sign_with_rsa_key(data, private_key):
+    """Signs *data* using *private_key*.
+
+    Function used to generate an RSA signature over provided data using a 3072-bit private key with
+    the public exponent of 3 (hard Intel SGX requirement on the key size and the exponent).
+    Suitable to be used as a callback to :py:func:`graminelibos.Sigstruct.sign()`.
+
+    Args:
+        data (bytes): Data to calculate the signature over.
+        private_key (cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey): RSA private key.
+
+    Returns:
+        (int, int, int): Tuple of exponent, modulus and signature respectively.
+    """
+
+    public_numbers = private_key.public_key().public_numbers()
+    assert public_numbers.e == SGX_RSA_PUBLIC_EXPONENT
+    signature = private_key.sign(data, padding.PKCS1v15(), hashes.SHA256())
+    return public_numbers.e, public_numbers.n, int.from_bytes(signature, byteorder='big')
 
 
 def generate_private_key():
@@ -598,6 +632,7 @@ def generate_private_key():
         key_size=SGX_RSA_KEY_SIZE,
         backend=_cryptography_backend)
 
+
 def generate_private_key_pem():
     """Generate PEM-encoded RSA key suitable for use with SGX