César Belley | dea01f6 | 2020-08-26 13:42:07 +0200 | [diff] [blame^] | 1 | #!/usr/bin/env python3 |
| 2 | # |
| 3 | # Libu2f-emu setup directory generator for USB U2F key emulation. |
| 4 | # |
| 5 | # Copyright (c) 2020 César Belley <cesar.belley@lse.epita.fr> |
| 6 | # Written by César Belley <cesar.belley@lse.epita.fr> |
| 7 | # |
| 8 | # This work is licensed under the terms of the GNU GPL, version 2 |
| 9 | # or, at your option, any later version. See the COPYING file in |
| 10 | # the top-level directory. |
| 11 | |
| 12 | import sys |
| 13 | import os |
| 14 | from random import randint |
| 15 | from typing import Tuple |
| 16 | |
| 17 | from cryptography.hazmat.backends import default_backend |
| 18 | from cryptography.hazmat.primitives.asymmetric import ec |
| 19 | from cryptography.hazmat.primitives.serialization import Encoding, \ |
| 20 | NoEncryption, PrivateFormat, PublicFormat |
| 21 | from OpenSSL import crypto |
| 22 | |
| 23 | |
| 24 | def write_setup_dir(dirpath: str, privkey_pem: bytes, cert_pem: bytes, |
| 25 | entropy: bytes, counter: int) -> None: |
| 26 | """ |
| 27 | Write the setup directory. |
| 28 | |
| 29 | Args: |
| 30 | dirpath: The directory path. |
| 31 | key_pem: The private key PEM. |
| 32 | cert_pem: The certificate PEM. |
| 33 | entropy: The 48 bytes of entropy. |
| 34 | counter: The counter value. |
| 35 | """ |
| 36 | # Directory |
| 37 | os.mkdir(dirpath) |
| 38 | |
| 39 | # Private key |
| 40 | with open(f'{dirpath}/private-key.pem', 'bw') as f: |
| 41 | f.write(privkey_pem) |
| 42 | |
| 43 | # Certificate |
| 44 | with open(f'{dirpath}/certificate.pem', 'bw') as f: |
| 45 | f.write(cert_pem) |
| 46 | |
| 47 | # Entropy |
| 48 | with open(f'{dirpath}/entropy', 'wb') as f: |
| 49 | f.write(entropy) |
| 50 | |
| 51 | # Counter |
| 52 | with open(f'{dirpath}/counter', 'w') as f: |
| 53 | f.write(f'{str(counter)}\n') |
| 54 | |
| 55 | |
| 56 | def generate_ec_key_pair() -> Tuple[str, str]: |
| 57 | """ |
| 58 | Generate an ec key pair. |
| 59 | |
| 60 | Returns: |
| 61 | The private and public key PEM. |
| 62 | """ |
| 63 | # Key generation |
| 64 | privkey = ec.generate_private_key(ec.SECP256R1, default_backend()) |
| 65 | pubkey = privkey.public_key() |
| 66 | |
| 67 | # PEM serialization |
| 68 | privkey_pem = privkey.private_bytes(encoding=Encoding.PEM, |
| 69 | format=PrivateFormat.TraditionalOpenSSL, |
| 70 | encryption_algorithm=NoEncryption()) |
| 71 | pubkey_pem = pubkey.public_bytes(encoding=Encoding.PEM, |
| 72 | format=PublicFormat.SubjectPublicKeyInfo) |
| 73 | return privkey_pem, pubkey_pem |
| 74 | |
| 75 | |
| 76 | def generate_certificate(privkey_pem: str, pubkey_pem: str) -> str: |
| 77 | """ |
| 78 | Generate a x509 certificate from a key pair. |
| 79 | |
| 80 | Args: |
| 81 | privkey_pem: The private key PEM. |
| 82 | pubkey_pem: The public key PEM. |
| 83 | |
| 84 | Returns: |
| 85 | The certificate PEM. |
| 86 | """ |
| 87 | # Convert key pair |
| 88 | privkey = crypto.load_privatekey(crypto.FILETYPE_PEM, privkey_pem) |
| 89 | pubkey = crypto.load_publickey(crypto.FILETYPE_PEM, pubkey_pem) |
| 90 | |
| 91 | # New x509v3 certificate |
| 92 | cert = crypto.X509() |
| 93 | cert.set_version(0x2) |
| 94 | |
| 95 | # Serial number |
| 96 | cert.set_serial_number(randint(1, 2 ** 64)) |
| 97 | |
| 98 | # Before / After |
| 99 | cert.gmtime_adj_notBefore(0) |
| 100 | cert.gmtime_adj_notAfter(4 * (365 * 24 * 60 * 60)) |
| 101 | |
| 102 | # Public key |
| 103 | cert.set_pubkey(pubkey) |
| 104 | |
| 105 | # Subject name and issueer |
| 106 | cert.get_subject().CN = "U2F emulated" |
| 107 | cert.set_issuer(cert.get_subject()) |
| 108 | |
| 109 | # Extensions |
| 110 | cert.add_extensions([ |
| 111 | crypto.X509Extension(b"subjectKeyIdentifier", |
| 112 | False, b"hash", subject=cert), |
| 113 | ]) |
| 114 | cert.add_extensions([ |
| 115 | crypto.X509Extension(b"authorityKeyIdentifier", |
| 116 | False, b"keyid:always", issuer=cert), |
| 117 | ]) |
| 118 | cert.add_extensions([ |
| 119 | crypto.X509Extension(b"basicConstraints", True, b"CA:TRUE") |
| 120 | ]) |
| 121 | |
| 122 | # Signature |
| 123 | cert.sign(privkey, 'sha256') |
| 124 | |
| 125 | return crypto.dump_certificate(crypto.FILETYPE_PEM, cert) |
| 126 | |
| 127 | |
| 128 | def generate_setup_dir(dirpath: str) -> None: |
| 129 | """ |
| 130 | Generates the setup directory. |
| 131 | |
| 132 | Args: |
| 133 | dirpath: The directory path. |
| 134 | """ |
| 135 | # Key pair |
| 136 | privkey_pem, pubkey_pem = generate_ec_key_pair() |
| 137 | |
| 138 | # Certificate |
| 139 | certificate_pem = generate_certificate(privkey_pem, pubkey_pem) |
| 140 | |
| 141 | # Entropy |
| 142 | entropy = os.urandom(48) |
| 143 | |
| 144 | # Counter |
| 145 | counter = 0 |
| 146 | |
| 147 | # Write |
| 148 | write_setup_dir(dirpath, privkey_pem, certificate_pem, entropy, counter) |
| 149 | |
| 150 | |
| 151 | def main() -> None: |
| 152 | """ |
| 153 | Main function |
| 154 | """ |
| 155 | # Dir path |
| 156 | if len(sys.argv) != 2: |
| 157 | sys.stderr.write(f'Usage: {sys.argv[0]} <setup_dir>\n') |
| 158 | exit(2) |
| 159 | dirpath = sys.argv[1] |
| 160 | |
| 161 | # Dir non existence |
| 162 | if os.path.exists(dirpath): |
| 163 | sys.stderr.write(f'Directory: {dirpath} already exists.\n') |
| 164 | exit(1) |
| 165 | |
| 166 | generate_setup_dir(dirpath) |
| 167 | |
| 168 | |
| 169 | if __name__ == '__main__': |
| 170 | main() |