Animal Crossing New Horizons font decryptor for .bfttf or .bfotf files

bfttf.py

# Animal Crossing New Horizons font decryptor for .bfttf or .bfotf files
# Usage: python3 bfttf.py input.bfttf output.ttf

from sys import argv

# might be other keys, who knows
key = [0x49, 0x62, 0x18, 0x06]

def xor(data, key):
  offset = 0
  byte = data.read(1)
  while byte:
    yield ord(byte) ^ key[offset % 4]
    offset += 1
    byte = data.read(1)

with open(argv[1], 'rb') as in_buffer:
  # lazy way to get file length - seek to the end, get the position, then seek back to the start
  in_buffer.seek(0, 2)
  in_size = in_buffer.tell()
  # skip 8-byte header(?)
  in_buffer.seek(8, 0)
  
  out_size = in_size - 8
  out_buffer = bytearray(out_size)

  with open(argv[2], 'wb') as f:
    f.write(bytes( [i for i in xor(in_buffer, key)] ))