1#!/usr/bin/env python3
2# SPDX-License-Identifier: GPL-2.0-only
3#
4# Public key to dtsi converter.
5#
6# Copyright (c) Siemens AG, 2022
7#
8
9from argparse import ArgumentParser, FileType
10from os.path import basename, splitext
11from Cryptodome.PublicKey import RSA
12from Cryptodome.Util.number import inverse
13
14def int_to_bytestr(n, length=None):
15    if not length:
16        length = (n.bit_length() + 7) // 8
17    byte_array = n.to_bytes(length, 'big')
18    return ' '.join(['{:02x}'.format(byte) for byte in byte_array])
19
20ap = ArgumentParser(description='Public key to dtsi converter')
21
22ap.add_argument('--hash', '-H', default='sha256',
23                help='hash to be used with key (default: sha256)')
24ap.add_argument('--required-conf', '-c', action='store_true',
25                help='mark key required for configuration')
26ap.add_argument('--required-image', '-i', action='store_true',
27                help='mark key required for image')
28ap.add_argument('--spl', '-s', action='store_true',
29                help='mark key for usage in SPL')
30ap.add_argument('key_file', metavar='KEY_FILE', type=FileType('r'),
31                help='key file (formats: X.509, PKCS#1, OpenSSH)')
32ap.add_argument('dtsi_file', metavar='DTSI_FILE', type=FileType('w'),
33                help='dtsi output file')
34
35args = ap.parse_args()
36
37key_name, _ = splitext(basename(args.key_file.name))
38
39key_data = args.key_file.read()
40key = RSA.importKey(key_data)
41
42r_squared = (2**key.size_in_bits())**2 % key.n
43n0_inverse = 2**32 - inverse(key.n, 2**32)
44
45out = args.dtsi_file
46out.write('/ {\n')
47out.write('\tsignature {\n')
48out.write('\t\tkey-{} {{\n'.format(key_name))
49out.write('\t\t\tkey-name-hint = "{}";\n'.format(key_name))
50out.write('\t\t\talgo = "{},rsa{}";\n'.format(args.hash, key.size_in_bits()))
51out.write('\t\t\trsa,num-bits = <{}>;\n'.format(key.size_in_bits()))
52out.write('\t\t\trsa,modulus = [{}];\n'.format(int_to_bytestr(key.n)))
53out.write('\t\t\trsa,exponent = [{}];\n'.format(int_to_bytestr(key.e, 8)))
54out.write('\t\t\trsa,r-squared = [{}];\n'.format(int_to_bytestr(r_squared)))
55out.write('\t\t\trsa,n0-inverse = <0x{:x}>;\n'.format(n0_inverse))
56if args.required_conf:
57    out.write('\t\t\trequired = "conf";\n')
58elif args.required_image:
59    out.write('\t\t\trequired = "image";\n')
60if args.spl:
61    out.write('\t\t\tu-boot,dm-spl;\n')
62out.write('\t\t};\n')
63out.write('\t};\n')
64out.write('};\n')
65