sb_hmac.py

#!/usr/bin/python3
#adapted from https://github.com/plutooo/smilehax/blob/master/scripts/make_script.py 
#all credits to plutooo

import sys
import struct
import hashlib
import hmac

HMAC_KEY = \
'''nqmby+e9S?{%U*-V]51n%^xZMk8>b{?x]&?(NmmV[,g85:%6Sqd"'U")/8u77UL2'''

if(len(sys.argv) != 3):
	print("Usage: python3 SMILEBASIC_FILENAME output_filename")
	exit(0)

buf = open(sys.argv[1], 'rb').read()

data_len = len(buf)

message = buf[:data_len-20]
footer_old = buf[data_len-20:]

h = hmac.new(bytearray(HMAC_KEY, 'utf-8'), digestmod=hashlib.sha1)
footer_calculated=h.update(message)
footer_calculated=h.digest()

print("message size:           %d bytes (header+script)" % (data_len-20))
print("hmac old footer:        %s" % footer_old.hex())
print("hmac calculated footer: %s" % footer_calculated.hex())

if footer_old == footer_calculated:
	print("hmac is already correct, exiting...")
	exit(0)

print("copying modified %s to %s" % (sys.argv[1],sys.argv[2]))
out = open(sys.argv[2], 'wb')
out.write(message+footer_calculated)
print("done")