https://github.com/nh2/antimersenne
Predicting Python's Mersenne twister PRNG for 30c3 CTF, with Python calling Java, yeah
https://github.com/nh2/antimersenne
Last synced: 3 months ago
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Predicting Python's Mersenne twister PRNG for 30c3 CTF, with Python calling Java, yeah
- Host: GitHub
- URL: https://github.com/nh2/antimersenne
- Owner: nh2
- Created: 2013-12-29T03:11:02.000Z (over 11 years ago)
- Default Branch: master
- Last Pushed: 2013-12-29T03:26:46.000Z (over 11 years ago)
- Last Synced: 2025-01-13T00:26:40.545Z (5 months ago)
- Language: Java
- Size: 109 KB
- Stars: 2
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
AntiMersenne
============
Predicting Python's Mersenne twister PRNG for 30c3 CTF, with Python calling Java, yeah
Running
-------
```
cd bin
./predict.py
```
Side notes
----------
* Had to fiddle around a bit with `sign()` between Python/Java because Java has no unsigned ints
* The Mersenne I've implemented in Java doesn't actually seem to generate Python's output even with the same internal state
* This didn't matter, I just read the observed generated pseudo-random numbers in Python, send them to Java, reconstruct the state there using `rev`, and set that state in Python with `r.setstate()`
* My observed input numbers are 64 bit, my Java reverser takes 32 bit numbers, so I un-concatenate them with `splitInto32()`
* Thanks to Ruth for the idea that I can convert a 32 bit int in Python to a 32 bit uint using `% (2*32)`
Sources
-------
* [Python's random docs, describing that Mersenne is used](http://docs.python.org/2/library/random.html)
* [Main article that helped me solve it](http://jazzy.id.au/default/2010/09/22/cracking_random_number_generators_part_3.html)
* [Similar proof of concept, but for cases where only 8 bit numbers are generated from the 32 bit output that Mersenne creates (randint(0, 255) just takes the first 8 bits)](https://spideroak.com/blog/20121205114003-exploit-information-leaks-in-random-numbers-from-python-ruby-and-php)
* [Similar thing for C#, not so well explained, but this shows how the thing would operate on uint32 which Java doesn't have](http://b10l.com/?p=24)
* [Python's random module](https://github.com/certik/python-2.7/blob/master/Lib/random.py)
* [Python's _random C module (much of the actual code)](https://github.com/certik/python-2.7/blob/master/Modules/_randommodule.c)
* [Not relevant for the cPython implementation, but interesting](http://code.activestate.com/recipes/578056-mersenne-twister/)