Offline BIP039 implementation using your own entropy.

offline_mnemonic_gen.py

import sys
import hashlib
import argparse
import binascii
import os
import math

def entropy_dice(entropy):
	dicesize=int(raw_input("Enter the number of faces each dieroll has (e.g. '6' or '20'): "))
	entval=0
	rolls=int(math.ceil(float(entropy)*math.log(2.0)/math.log(dicesize)))
	for x in range(rolls):
		entry=int(raw_input("Enter the value (1-%d) of dice %d/%d: " % (dicesize,x+1,rolls))) % dicesize
		entval+=entry
		entval*=dicesize
	return entval
def entropy_hex(entropy):
	return int(raw_input(("Please enter a %d-bit (%d character) hex string:\n") % (entropy,entropy/4)),16)
def entropy_bin(entropy):
	return int(raw_input("Please enter a %d-bit binary string:\n") % (entropy),2)
def entropy_generic(entropy):
	entval=0
	entamount=0
	while(entamount < entropy):
		print("Entropy so far: %f / %d\n" % (entamount,entropy))
		dicesize=int(raw_input("Enter the number of possiblities for the next source: "))
		entry=int(raw_input("Enter the value of the next source: ")) % dicesize
		entval+=entry
		entval*=dicesize
	return entval
def entropy_system(entropy):
	return int(binascii.hexlify(os.urandom(entropy/8)),16)

entropy_modes={'dice':entropy_dice,'hex':entropy_hex,'bin':entropy_bin,'generic':entropy_generic,'system':entropy_system}

parser=argparse.ArgumentParser(description='Generate a valid offline HD wallet mnemonic from personal entropy')
parser.add_argument('--mode','-m',default='hex',help='Choose the mode of gathering entropy',choices=entropy_modes.keys())
parser.add_argument('--entropy_size','-s',default=128,type=int,help='The number of bits of entropy',choices=[128,160,192,224,256])
parser.add_argument('--wordlist','-w',type=argparse.FileType('r'),help='The 2048 wordlist text file to use',required=True)

args=parser.parse_args()
checksum_size=args.entropy_size//32

wordlist=list(args.wordlist)

entint=entropy_modes[args.mode](args.entropy_size) & (2**args.entropy_size  - 1)

entbytes=binascii.unhexlify(hex(entint)[2:].zfill(args.entropy_size//4).strip("L"))
hd=hashlib.sha256(entbytes).hexdigest()
csint=int(hd,16) >> (256-checksum_size)
mnemonic_size=(args.entropy_size+checksum_size)/11
mint=(entint << checksum_size) | csint

backwords=[wordlist[(mint >> (11*x)) & 0x7FF].strip() for x in range(mnemonic_size)]
words=reversed(backwords)

print("Your words are:\n\n")
print(' '.join(words))