CODEWITHSUNDEEP
pythonrandomcryptographypasswords
baliao
baliao

Reputation: 173

Why does using this code can generate a random password?

Here a snippet for generating password code, I have 2 questions about this, Could you please share how to understand?

  1. urandom(6), help from urandom said,return n random bytes suitable for cryptographic use, it is say, it will return 6 bytes, is it 6 of ASCII ?

  2. ord(c) , get the decimal base for above bytes, why here transfer to decimal base?

Help for urandom:

def urandom(n): # real signature unknown; restored from __doc__
    """
    urandom(n) -> str

    Return n random bytes suitable for cryptographic use.
    """
    return ""

Python script:

from os import urandom
letters = "ABCDEFGHJKLMNPRSTUVWXYZ"
password = "".join(letters[ord(c) % len(letters)] for c in urandom(6))

Upvotes: 2

Views: 111

Answers (2)

Vasu Deo.S
Vasu Deo.S

Reputation: 1850

ord() function takes in a string containing a single character, and returns its Unicode index.

ex. 

ord("A") => 65
ord("£") => 163

It is not used to get the decimal base of a byte as you mentioned, but rather its Unicode Index (its place in the Unicode Table).

P.S. :- Even though it returns the Unicode index but that doesn't mean its, range = len(Unicode Table) , the reason being that your python compiler may not support such long character sets under normal circumstances.

Upvotes: 1

Selcuk
Selcuk

Reputation: 59164

urandom will return a byte (i.e. a value between 0 and 255). The sample code uses that value and the modulo operator (%) to convert it into a value between 0 and 22, so that it can return one of the 23 letters (I, O, and Q are excluded not to be confused with numbers).

Note that it is not a perfectly balanced algorithm as it would favour the first 3 letters (A, B, and C) more, because 256 is not divisible by 23 and 256 % 23 is 3.

Upvotes: 5

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