#!/usr/bin/python
'''
    Use this script to cross-check that TREZOR generated valid
    mnemonic sentence for given internal (TREZOR-generated)
    and external (computer-generated) entropy.
'''

import binascii
import hashlib
import mnemonic

def generate_entropy(strength, internal_entropy, external_entropy):
    '''
    strength - length of produced seed. One of 128, 192, 256
    random - binary stream of random data from external HRNG
    '''
    if strength not in (128, 192, 256):
        raise Exception("Invalid strength")

    if not internal_entropy:
        raise Exception("Internal entropy is not provided")

    if len(internal_entropy) < 32:
        raise Exception("Internal entropy too short")

    if not external_entropy:
        raise Exception("External entropy is not provided")

    if len(external_entropy) < 32:
        raise Exception("External entropy too short")

    entropy = hashlib.sha256(internal_entropy + external_entropy).digest()
    entropy_stripped = entropy[:strength / 8]

    if len(entropy_stripped) * 8 != strength:
        raise Exception("Entropy length mismatch")

    return entropy_stripped

def main():
    comp = binascii.unhexlify(raw_input("Please enter computer-generated entropy (in hex): ").strip())
    trzr = binascii.unhexlify(raw_input("Please enter TREZOR-generated entropy (in hex): ").strip())
    word_count = int(raw_input("How many words your mnemonic has? "))

    strength = word_count * 32 / 3

    entropy = generate_entropy(strength, trzr, comp)

    words = mnemonic.Mnemonic('english').to_mnemonic(entropy)
    if not mnemonic.Mnemonic('english').check(words):
        print "Mnemonic is invalid"
        return

    if len(words.split(' ')) != word_count:
        print "Mnemonic length mismatch!"
        return

    print "Generated mnemonic is:", words

if __name__ == '__main__':
    main()