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tools: Add script for converting public key into device tree include

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Allows to create a public key device tree dtsi for inclusion into U-Boot
SPL and proper during first build already. This can be achieved via
CONFIG_DEVICE_TREE_INCLUDES.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
This commit is contained in:
Jan Kiszka 2023-02-28 19:19:16 +01:00 committed by Tom Rini
parent 430e9f6666
commit 75c89069f0
1 changed files with 64 additions and 0 deletions
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64
tools/key2dtsi.py Executable file
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#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-2.0-only
#
# Public key to dtsi converter.
#
# Copyright (c) Siemens AG, 2022
#
from argparse import ArgumentParser, FileType
from os.path import basename, splitext
from Cryptodome.PublicKey import RSA
from Cryptodome.Util.number import inverse
def int_to_bytestr(n, length=None):
if not length:
length = (n.bit_length() + 7) // 8
byte_array = n.to_bytes(length, 'big')
return ' '.join(['{:02x}'.format(byte) for byte in byte_array])
ap = ArgumentParser(description='Public key to dtsi converter')
ap.add_argument('--hash', '-H', default='sha256',
help='hash to be used with key (default: sha256)')
ap.add_argument('--required-conf', '-c', action='store_true',
help='mark key required for configuration')
ap.add_argument('--required-image', '-i', action='store_true',
help='mark key required for image')
ap.add_argument('--spl', '-s', action='store_true',
help='mark key for usage in SPL')
ap.add_argument('key_file', metavar='KEY_FILE', type=FileType('r'),
help='key file (formats: X.509, PKCS#1, OpenSSH)')
ap.add_argument('dtsi_file', metavar='DTSI_FILE', type=FileType('w'),
help='dtsi output file')
args = ap.parse_args()
key_name, _ = splitext(basename(args.key_file.name))
key_data = args.key_file.read()
key = RSA.importKey(key_data)
r_squared = (2**key.size_in_bits())**2 % key.n
n0_inverse = 2**32 - inverse(key.n, 2**32)
out = args.dtsi_file
out.write('/ {\n')
out.write('\tsignature {\n')
out.write('\t\tkey-{} {{\n'.format(key_name))
out.write('\t\t\tkey-name-hint = "{}";\n'.format(key_name))
out.write('\t\t\talgo = "{},rsa{}";\n'.format(args.hash, key.size_in_bits()))
out.write('\t\t\trsa,num-bits = <{}>;\n'.format(key.size_in_bits()))
out.write('\t\t\trsa,modulus = [{}];\n'.format(int_to_bytestr(key.n)))
out.write('\t\t\trsa,exponent = [{}];\n'.format(int_to_bytestr(key.e, 8)))
out.write('\t\t\trsa,r-squared = [{}];\n'.format(int_to_bytestr(r_squared)))
out.write('\t\t\trsa,n0-inverse = <0x{:x}>;\n'.format(n0_inverse))
if args.required_conf:
out.write('\t\t\trequired = "conf";\n')
elif args.required_image:
out.write('\t\t\trequired = "image";\n')
if args.spl:
out.write('\t\t\tu-boot,dm-spl;\n')
out.write('\t\t};\n')
out.write('\t};\n')
out.write('};\n')