scripts/pem_to_pub_c.py

#!/usr/bin/env python3
# SPDX-License-Identifier: BSD-2-Clause
#
# Copyright (c) 2015, Linaro Limited


def get_args():
    import argparse

    parser = argparse.ArgumentParser()
    parser.add_argument(
        '--prefix', required=True,
        help='Prefix for the public key exponent and modulus in c file')
    parser.add_argument(
        '--out', required=True,
        help='Name of c file for the public key')
    parser.add_argument('--key', required=True, help='Name of key file')

    return parser.parse_args()


def main():
    import array
    from Crypto.PublicKey import RSA
    from Crypto.Util.number import long_to_bytes

    args = get_args()

    with open(args.key, 'r') as f:
        key = RSA.importKey(f.read())

    # Refuse public exponent with more than 32 bits. Otherwise the C
    # compiler may simply truncate the value and proceed.
    # This will lead to TAs seemingly having invalid signatures with a
    # possible security issue for any e = k*2^32 + 1 (for any integer k).
    if key.publickey().e > 0xffffffff:
        raise ValueError(
            'Unsupported large public exponent detected. ' +
            'OP-TEE handles only public exponents up to 2^32 - 1.')

    with open(args.out, 'w') as f:
        f.write("#include <stdint.h>\n")
        f.write("#include <stddef.h>\n\n")
        f.write("const uint32_t " + args.prefix + "_exponent = " +
                str(key.publickey().e) + ";\n\n")
        f.write("const uint8_t " + args.prefix + "_modulus[] = {\n")
        i = 0
        for x in array.array("B", long_to_bytes(key.publickey().n)):
            f.write("0x" + '{0:02x}'.format(x) + ",")
            i = i + 1
            if i % 8 == 0:
                f.write("\n")
            else:
                f.write(" ")
        f.write("};\n")
        f.write("const size_t " + args.prefix + "_modulus_size = sizeof(" +
                args.prefix + "_modulus);\n")


if __name__ == "__main__":
    main()