What's the best way to generate random strings

Question

For a project, I need a method of creating thousands of random strings while keeping collisions low. I'm looking for them to be only 12 characters long and uppercase only. Any suggestions?

Answer 1

For cryptographically strong pseudo-random bytes you might use the pyOpenSSL wrapper around OpenSSL.

It provides the bytes function to gather a pseudo-random sequences of bytes.

from OpenSSL import rand

b = rand.bytes(7)

_{BTW, 12 uppercase letters is a little bit more that 56 bits of entropy. You will only to have to read 7 bytes.}

Answer 2

By Django, you can use get_random_string function in django.utils.crypto module.

get_random_string(length=12,
    allowed_chars=u'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789')
    Returns a securely generated random string.

    The default length of 12 with the a-z, A-Z, 0-9 character set returns
    a 71-bit value. log_2((26+26+10)^12) =~ 71 bits

Example:

get_random_string()
u'ngccjtxvvmr9'

get_random_string(4, allowed_chars='bqDE56')
u'DDD6'

But if you don't want to have Django, here is independent code of it:

Code:

import random
import hashlib
import time

SECRET_KEY = 'PUT A RANDOM KEY WITH 50 CHARACTERS LENGTH HERE !!'

try:
    random = random.SystemRandom()
    using_sysrandom = True
except NotImplementedError:
    import warnings
    warnings.warn('A secure pseudo-random number generator is not available '
                  'on your system. Falling back to Mersenne Twister.')
    using_sysrandom = False


def get_random_string(length=12,
                      allowed_chars='abcdefghijklmnopqrstuvwxyz'
                                    'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'):
    """
    Returns a securely generated random string.

    The default length of 12 with the a-z, A-Z, 0-9 character set returns
    a 71-bit value. log_2((26+26+10)^12) =~ 71 bits
    """
    if not using_sysrandom:
        # This is ugly, and a hack, but it makes things better than
        # the alternative of predictability. This re-seeds the PRNG
        # using a value that is hard for an attacker to predict, every
        # time a random string is required. This may change the
        # properties of the chosen random sequence slightly, but this
        # is better than absolute predictability.
        random.seed(
            hashlib.sha256(
                ("%s%s%s" % (
                    random.getstate(),
                    time.time(),
                    SECRET_KEY)).encode('utf-8')
            ).digest())
    return ''.join(random.choice(allowed_chars) for i in range(length))

Answer 3

This function generates random string of UPPERCASE letters with the specified length,

eg: length = 6, will generate the following random sequence pattern

YLNYVQ

    import random as r

    def generate_random_string(length):
        random_string = ''
        random_str_seq = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        for i in range(0,length):
            if i % length == 0 and i != 0:
                random_string += '-'
            random_string += str(random_str_seq[r.randint(0, len(random_str_seq) - 1)])
        return random_string

Answer 4

Could make a generator:

from string import ascii_uppercase
import random
from itertools import islice

def random_chars(size, chars=ascii_uppercase):
    selection = iter(lambda: random.choice(chars), object())
    while True:
        yield ''.join(islice(selection, size))

random_gen = random_chars(12)
print next(random_gen)
# LEQIITOSJZOQ
print next(random_gen)
# PXUYJTOTHWPJ

Then just pull from the generator when they're needed... Either using next(random_gen) when you need them, or use random_200 = list(islice(random_gen, 200)) for instance...

Answer 5

CODE:

from random import choice
from string import ascii_uppercase

print(''.join(choice(ascii_uppercase) for i in range(12)))

OUTPUT:

5 examples:

QPUPZVVHUNSN
EFJACZEBYQEB
QBQJJEEOYTZY
EOJUSUEAJEEK
QWRWLIWDTDBD

---

EDIT:

If you need only digits, use the digits constant instead of the ascii_uppercase one from the string module.

3 examples:

229945986931
867348810313
618228923380