scripts: Add u2f-setup-gen script

This patch adds the script used to generate setup directories, needed
for the device u2f-emulated configuration in directory mode:

    python u2f-setup-gen.py $DIR
    qemu -usb -device u2f-emulated,dir=$DIR

Signed-off-by: César Belley <cesar.belley@lse.epita.fr>
Message-id: 20200826114209.28821-11-cesar.belley@lse.epita.fr
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

scripts/u2f-setup-gen.py

@@ -0,0 +1,170 @@
+#!/usr/bin/env python3
+#
+# Libu2f-emu setup directory generator for USB U2F key emulation.
+#
+# Copyright (c) 2020 César Belley <cesar.belley@lse.epita.fr>
+# Written by César Belley <cesar.belley@lse.epita.fr>
+#
+# This work is licensed under the terms of the GNU GPL, version 2
+# or, at your option, any later version.  See the COPYING file in
+# the top-level directory.
+
+import sys
+import os
+from random import randint
+from typing import Tuple
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.asymmetric import ec
+from cryptography.hazmat.primitives.serialization import Encoding, \
+    NoEncryption, PrivateFormat, PublicFormat
+from OpenSSL import crypto
+
+
+def write_setup_dir(dirpath: str, privkey_pem: bytes, cert_pem: bytes,
+                    entropy: bytes, counter: int) -> None:
+    """
+    Write the setup directory.
+
+    Args:
+        dirpath: The directory path.
+        key_pem: The private key PEM.
+        cert_pem: The certificate PEM.
+        entropy: The 48 bytes of entropy.
+        counter: The counter value.
+    """
+    # Directory
+    os.mkdir(dirpath)
+
+    # Private key
+    with open(f'{dirpath}/private-key.pem', 'bw') as f:
+        f.write(privkey_pem)
+
+    # Certificate
+    with open(f'{dirpath}/certificate.pem', 'bw') as f:
+        f.write(cert_pem)
+
+    # Entropy
+    with open(f'{dirpath}/entropy', 'wb') as f:
+        f.write(entropy)
+
+    # Counter
+    with open(f'{dirpath}/counter', 'w') as f:
+        f.write(f'{str(counter)}\n')
+
+
+def generate_ec_key_pair() -> Tuple[str, str]:
+    """
+    Generate an ec key pair.
+
+    Returns:
+        The private and public key PEM.
+    """
+    # Key generation
+    privkey = ec.generate_private_key(ec.SECP256R1, default_backend())
+    pubkey = privkey.public_key()
+
+    # PEM serialization
+    privkey_pem = privkey.private_bytes(encoding=Encoding.PEM,
+                                        format=PrivateFormat.TraditionalOpenSSL,
+                                        encryption_algorithm=NoEncryption())
+    pubkey_pem = pubkey.public_bytes(encoding=Encoding.PEM,
+                                     format=PublicFormat.SubjectPublicKeyInfo)
+    return privkey_pem, pubkey_pem
+
+
+def generate_certificate(privkey_pem: str, pubkey_pem: str) -> str:
+    """
+    Generate a x509 certificate from a key pair.
+
+    Args:
+        privkey_pem: The private key PEM.
+        pubkey_pem: The public key PEM.
+
+    Returns:
+        The certificate PEM.
+    """
+    # Convert key pair
+    privkey = crypto.load_privatekey(crypto.FILETYPE_PEM, privkey_pem)
+    pubkey = crypto.load_publickey(crypto.FILETYPE_PEM, pubkey_pem)
+
+    # New x509v3 certificate
+    cert = crypto.X509()
+    cert.set_version(0x2)
+
+    # Serial number
+    cert.set_serial_number(randint(1, 2 ** 64))
+
+    # Before / After
+    cert.gmtime_adj_notBefore(0)
+    cert.gmtime_adj_notAfter(4 * (365 * 24 * 60 * 60))
+
+    # Public key
+    cert.set_pubkey(pubkey)
+
+    # Subject name and issueer
+    cert.get_subject().CN = "U2F emulated"
+    cert.set_issuer(cert.get_subject())
+
+    # Extensions
+    cert.add_extensions([
+        crypto.X509Extension(b"subjectKeyIdentifier",
+                             False, b"hash", subject=cert),
+    ])
+    cert.add_extensions([
+        crypto.X509Extension(b"authorityKeyIdentifier",
+                             False, b"keyid:always", issuer=cert),
+    ])
+    cert.add_extensions([
+        crypto.X509Extension(b"basicConstraints", True, b"CA:TRUE")
+    ])
+
+    # Signature
+    cert.sign(privkey, 'sha256')
+
+    return crypto.dump_certificate(crypto.FILETYPE_PEM, cert)
+
+
+def generate_setup_dir(dirpath: str) -> None:
+    """
+    Generates the setup directory.
+
+    Args:
+        dirpath: The directory path.
+    """
+    # Key pair
+    privkey_pem, pubkey_pem = generate_ec_key_pair()
+
+    # Certificate
+    certificate_pem = generate_certificate(privkey_pem, pubkey_pem)
+
+    # Entropy
+    entropy = os.urandom(48)
+
+    # Counter
+    counter = 0
+
+    # Write
+    write_setup_dir(dirpath, privkey_pem, certificate_pem, entropy, counter)
+
+
+def main() -> None:
+    """
+    Main function
+    """
+    # Dir path
+    if len(sys.argv) != 2:
+        sys.stderr.write(f'Usage: {sys.argv[0]} <setup_dir>\n')
+        exit(2)
+    dirpath = sys.argv[1]
+
+    # Dir non existence
+    if os.path.exists(dirpath):
+        sys.stderr.write(f'Directory: {dirpath} already exists.\n')
+        exit(1)
+
+    generate_setup_dir(dirpath)
+
+
+if __name__ == '__main__':
+    main()