#!/usr/bin/env python3
# python -I solve.py files/beacon_flash.bin
import sys
d = open(sys.argv[1] if len(sys.argv) > 1 else 'files/beacon_flash.bin', 'rb').read()
M = 0xffffffff
# DROM: vaddr 0x42030020 <-> file 0x10020 ; code ref'd 0x42039d20/30/40
def drom(va): return 0x10020 + (va - 0x42030020)
def cstr(va):
    o = drom(va); return d[o:d.index(b'\0', o)]
s_id, s_board = cstr(0x42039d20), cstr(0x42039d30)
ct = d[drom(0x42039d40):drom(0x42039d40) + 31]
def fnv(b):
    h = 0x811c9dc5
    for c in b: h = ((h ^ c) * 0x01000193) & M
    return h
rotl = lambda x, n: ((x << n) | (x >> (32 - n))) & M
h1, h2 = fnv(s_board), fnv(s_id)          # a4, a5
code = rotl(h1, 7) ^ h2
print('id=%r board=%r' % (s_id, s_board))
print('activation code: %08x' % code)
a4, a5 = h1, h2
out = bytearray()
for c in ct:
    a1 = ((a5 >> 19) | (a4 << 13)) & M; a6 = (a5 << 13) & M
    a4 ^= a1; a5 ^= a6
    a1 = ((a5 >> 7) | (a4 << 25)) & M; a6 = a4 >> 7
    a5 ^= a1; a4 ^= a6
    a1 = ((a5 >> 15) | (a4 << 17)) & M
    a4 ^= a1
    a5 ^= (a5 << 17) & M
    out.append(c ^ (a5 & 0xff))
print(out.decode(errors='replace'))