trezor-firmware/tools/build_vendorheader

#!/usr/bin/env python3
import sys
import struct
import re
import binascii
import os
import imp

png2toi = imp.load_source('png2toi', os.path.dirname(__file__) + '/png2toi')

# encode vendor name, add length byte and padding to multiple of 4
def encodevendor(vname):
    vbin = vname.encode('utf-8')
    vbin = struct.pack('<B',len(vbin)) + vbin
    vbin += b'\0' * (-len(vbin) & 3)
    return vbin

def encodekey(key):
    if len(key) != 64:
        raise Exception("Wrong key length")
    return binascii.unhexlify(key)

def main():
    if len(sys.argv) < 7:
        print('Usage build_vendorheader key1hex,... m version vendorname vendorimage.png vendorimage.bin')
        return 1

    keys = [encodekey(x) for x in sys.argv[1].split(',')]
    m = int(sys.argv[2])
    (vmajor, vminor) = [int(x) for x in sys.argv[3].split('.')]
    vname = sys.argv[4]
    ifn = sys.argv[5]
    ofn = sys.argv[6]
    if not ifn.endswith('.png'):
        print('Must provide PNG file')
        return 2

    expiry = 0
    vheader = b'TRZV' + struct.pack('<IIBBBB', 0, expiry, vmajor, vminor, m, len(keys))
    for k in keys:
        vheader += k
    vheader += encodevendor(vname) + png2toi.process_image(ifn)
    padding = 65 + (-len(vheader) - 65) & 511
    vheader += b'\0' * padding

    # put in length
    vheader = vheader[0:4] + struct.pack('<I', len(vheader)) + vheader[8:]

    with open(ofn, 'wb') as f:
        f.write(vheader)

main()