import random


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
    """
    return ''.join([random.choice(allowed_chars) for i in range(length)])