Python generate random 128 bit strings

Question

I need to generate several random strings for later use of length 128 bit (or 16 bytes, 32 hex characters). I have used this until now:

hex(random.getrandbits(128))[2:]

Unfortunately it turns out that it does not consistently produce 32 hex characters which is a requirement of my implementation. Some strings it produces are shorter than others, i.e. 30 or 31 characters, which is a problem.

Is there another way to achieve this?

When they're shorter, that just means the first bits came out all 0s. You could pad it back to the target length without modifying the distribution. — Charles Duffy
– Charles Duffy, Commented Apr 6, 2024 at 16:21

jamylak · Accepted Answer · 2013-04-27 02:35:09Z

3

>>> import os
>>> os.urandom(16)
'S\x0e\xac\x91m\xcf\xf1\xae\x9b5\xf9A\xf3\xa2\xf9@'

answered Apr 27, 2013 at 2:35

jamylak

134k30 gold badges238 silver badges240 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Asclepius · Accepted Answer · 2024-04-06 16:50:35Z

1

This approach should consistently produce a printable 32 character hex string from a pseudorandom 128 bit integer. It left pads with zeros, of course. Moreover, I believe this to be the simplest way to do it.

> import random

> randint = random.getrandbits(128)
> randstr = f'{randint:032x}'
> print(randstr)
00424c4bcbd1c00e3f4dd2bc52b2776b

Here is the code to test the output length:

import random

for i in range(1_000_000):
    randint = random.getrandbits(128)
    randstr = f'{randint:032x}'
    assert isinstance(randstr, str)
    assert (randint == int(randstr, 16)), (randint, randstr)
    assert (len(randstr) == 32), (randstr, len(randstr))
    assert (randstr == randstr.strip()), repr(randstr)
    print(randstr)

edited Apr 6, 2024 at 16:50

answered Aug 27, 2020 at 23:02

Asclepius

64.6k20 gold badges188 silver badges164 bronze badges

1 Comment

Asclepius Over a year ago

@Turing101 The answer has been rewritten and simplified to avoid the unnecessary use of encode and decode both.

Collectives™ on Stack Overflow

Python generate random 128 bit strings

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related