#!/usr/bin/env python
# example usage: ./rng_entropy_collector.py stm32_rng_1.dat 1048576
# note: for reading large amounts of entropy, compile a firmware
# that has DEBUG_RNG == 1 as that will disable the user button
# push confirmation

from __future__ import print_function
import binascii
import io
import sys
from trezorlib.client import TrezorClient
from trezorlib.transport_hid import HidTransport

def get_client():
    devices = HidTransport.enumerate()   # List all connected TREZORs on USB
    if len(devices) == 0:                # Check whether we found any
        return None
    transport = HidTransport(devices[0]) # Use first connected device
    return TrezorClient(transport)       # Creates object for communicating with TREZOR

def main():
    client = get_client()
    if not client:
        print('No TREZOR connected')
        return

    arg1 = sys.argv[1] # output file
    arg2 = int(sys.argv[2], 10) # total number of how many bytes of entropy to read
    step = 1024 if arg2 >= 1024 else arg2 # trezor will only return 1KB at a time

    with io.open(arg1, 'wb') as f:
        for i in xrange(0, arg2, step):
            entropy = client.get_entropy(step)
            f.write(entropy)

    client.close()

if __name__ == '__main__':
    main()