Generate memorable passwords

memorable_pwd.py

#!/usr/bin/python


import sys
import optparse
import random


rndgen = random.SystemRandom()
words = list(s.rstrip() for s in open("/usr/share/dict/words"))
punctuation = "!\"#&'()*,-./:;?@[\\]_{}"
digits = "0123456789"

def gen_memorable_pwd(pwd_len):
    """Generate passwords with an algorithm similar to the Password
    Assistant's 'memorable' kind - two random words with a random number
    and punctuation between."""
    
    global rndgen
    global words
    global punctuation
    global digits
    
    while True:
        # Grab two random words.
        word1, word2 = rndgen.sample(words, 2)
        # Make sure that they aren't so long that we can't fit a random number
        # and punctuation inbetween, and not too short so we need more than 9
        # digits.
        sum_len = len(word1) + len(word2)
        max_word_len = pwd_len - 2
        min_word_len = pwd_len - 11
        if sum_len > max_word_len or sum_len < min_word_len:
            continue
        # Generate a random number to pad the password.
        rand_num_list = rndgen.sample(digits, pwd_len - sum_len- 1)
        # Convert the list of numbers to a string.
        rand_num = "".join(str(n) for n in rand_num_list)
        # Join the parts with random punctuation.
        return "%s%s%s%s" % (
            word1,
            rand_num,
            rndgen.sample(punctuation, 1)[0],
            word2,
        )
    
def gen_xkcd_pwd(num_words):
    """Pick random words, e.g. 'correct horse battery staple'."""
    
    global rndgen
    global words
    
    return " ".join(rndgen.sample(words, num_words))
    

def main(argv):
    p = optparse.OptionParser()
    p.set_usage("""Usage: %prog [options]""")
    p.add_option("-l", "--length", type=int, dest="length",
                 help="Password length.")
    p.add_option("-c", "--count", type=int, dest="count", default=10,
                 help="Number of passwords to generate.")
    p.add_option("-x", "--xkcd", action="store_true", dest="xkcd",
                 help="Use xkcd algorithm instead.")
    options, argv = p.parse_args(argv)
    if len(argv) != 1:
        print >>sys.stderr, p.get_usage()
        return 1
    
    if options.xkcd:
        pwd_func = gen_xkcd_pwd
        default_len = 4
        if options.length is not None and options.length < 2:
            sys.exit("Too short!")
    else:
        pwd_func = gen_memorable_pwd
        default_len = 12
        if options.length is not None and options.length < 8:
            sys.exit("Too short!")
        elif options.length is not None and options.length > 31:
            sys.exit("Too long!")
    
    for i in range(options.count):
        print pwd_func(options.length or default_len)
    
    return 0
    

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