OpenSystemsDevelopment / usbboot

Authored by Tim Gover 2022-10-11 11:18:33 +0100

Add a Python utility script to converts RSA public keys
from PEM format to the binary format required by the bootloader
and vice-versa.

Showing 1 changed file with 49 additions and 0 deletions

tools/rpi-bootloader-key-convert 0 → 100755

	1	+#!/usr/bin/env python3
	2	+
	3	+import argparse
	4	+import struct
	5	+import sys
	6	+
	7	+from Cryptodome.PublicKey import RSA
	8	+
	9	+def bintopem(infile, outf):
	10	+ f = open(infile, 'rb')
	11	+ arr = f.read(264)
	12	+
	13	+ n = int.from_bytes(struct.unpack_from("256B", arr, 0), 'little')
	14	+ e = struct.unpack_from("<Q", arr, 256)[0]
	15	+ pubkey = RSA.construct((n, e))
	16	+ outf.write(pubkey.exportKey())
	17	+
	18	+def pemtobin(infile, outf):
	19	+ key = RSA.importKey(open(infile, 'r').read())
	20	+
	21	+ if key.size_in_bits() != 2048:
	22	+ raise Exception("RSA key size must be 2048")
	23	+
	24	+ # Extract the public key componenet n,e and store as little endian
	25	+ outf.write(key.n.to_bytes(256, byteorder='little'))
	26	+ outf.write(key.e.to_bytes(8, byteorder='little'))
	27	+
	28	+def main():
	29	+ parser = argparse.ArgumentParser('Converts RSA keys between PEM format and the raw binary format used by the Raspberry Pi 4 bootloader')
	30	+ parser.add_argument('input', nargs='+')
	31	+ parser.add_argument('--inform', default="pem")
	32	+ parser.add_argument('--output', required=False)
	33	+
	34	+ args = parser.parse_args()
	35	+
	36	+ if args.output:
	37	+ outf = open(args.output, 'wb')
	38	+ else:
	39	+ outf = sys.stdout.buffer
	40	+
	41	+ if args.inform == "pem":
	42	+ pemtobin(args.input[0], outf)
	43	+ elif args.inform == "bin":
	44	+ bintopem(args.input[0], outf)
	45	+ else:
	46	+ raise Exception("Unknown format %s" % args.inform)
	47	+
	48	+if __name__ == '__main__':
	49	+ main()
...	...