passgen

#!/usr/bin/env python3

import os, sys, math, random, subprocess as sp


def main(args=None):
	import argparse
	parser = argparse.ArgumentParser(
		description='Generate random passphrase'
			' using Diceware method and aspell "en" dictionary.')
	parser.add_argument('-w', '--words', metavar='n', type=int, default=5,
		help='Passphrase word count (default: %(default)s).')
	parser.add_argument('-f', '--char-count-min', metavar='n', type=int, default=20,
		help='Min passphrase character count (default: %(default)s).')
	parser.add_argument('-t', '--char-count-max', metavar='n', type=int, default=60,
		help='Max passphrase character count (default: %(default)s).')
	parser.add_argument('-i', '--id', metavar='string',
		help='Add some ID string (with randomized separator) to one of the words.')
	parser.add_argument('-e', '--entropy-estimate', action='store_true',
		help='Print rough entropy estimate of the'
			' resulting passphrase (not counting the --id, if any).')
	opts = parser.parse_args()

	aspell = sp.run(['aspell', '-d', 'en', 'dump', 'master'], check=True, stdout=sp.PIPE)
	aspell_words = list(set(aspell.stdout.decode().splitlines()))
	aspell_words_ent = math.log(len(aspell_words), 2)

	def get_word():
		word = random.choice(aspell_words)
		if word.endswith("'s"): word = word[:-2]
		return word

	words = list(get_word() for n in range(opts.words))
	tries, a, b = 999, opts.char_count_min, opts.char_count_max
	for n in range(tries):
		words_len = sum(map(len, words))
		if a <= words_len <= b: break
		words[random.choice(range(len(words)))] = get_word()
	else: parser.error(f'Failed to pick password of {a}-{b} chars within {tries} attempts')

	if opts.id:
		id_sep = random.choice('#@$%&^*!<>/?\|')
		n = random.choice(range(len(words)))
		words[n] = ''.join( [opts.id, id_sep, words[n]]
			if random.random() > 0.5 else [words[n], id_sep, opts.id] )

	print(' '.join(words))
	if opts.entropy_estimate:
		print('Entropy estimate: {:,.1f}b'.format(aspell_words_ent * len(words)))

if __name__ == '__main__': sys.exit(main())