Python Cookbook

Generating Non-Totally Random Passwords

Credit: Luther Blissett

Problem

You need to create new passwords randomly—for example, to assign them automatically to new user accounts—and want the passwords to be somewhat feasible to remember for typical users, so they won’t be written down.

Solution

We can use a pastiche approach for this, mimicking letter n-grams in actual English words. A grander way to look at the same approach is to call it a Markov Chain simulation of English:

import random, string

class password:
    # Any substantial file of English words will do just as well
    data = open("/usr/share/dict/words").read().lower(  )
    def renew(self, n, maxmem=3):
        self.chars = []
        for i in range(n):
            # Randomly "rotate" self.data
            randspot = random.randrange(len(self.data))
            self.data = self.data[randspot:] + self.data[:randspot]
            where = -1
            # Get the n-gram
            locate = ''.join(self.chars[-maxmem:])
            while where<0 and locate:
                # Locate the n-gram in the data
                where = self.data.find(locate)
                # Back off to a shorter n-gram if necessary
                locate = locate[1:]
            c = self.data[where+len(locate)+1] if not c.islower( ): c = random.choice(string.lowercase) self.chars.append(c) def _ _str_ _(self): return ''.join(self.chars) if _ _name_ _ == '_ _main_ _': "Usage: pastiche [passwords [length [memory]]]" import sys if len(sys.argv)>1: dopass = int(sys.argv[1]) else: dopass = 8 if len(sys.argv)>2: length = int(sys.argv[2]) else: length = 10 if len(sys.argv)>3: memory = int(sys.argv[3]) else: memory = 3 onepass = password( ...