This is a set of [Python][] bindings for the [scrypt][] key derivation function.
Scrypt is useful when encrypting password as it is possible to specify a minimum amount of time to use when encrypting and decrypting. If, for example, a password takes 0.05 seconds to verify, a user won’t notice the slight delay when signing in, but doing a brute force search of several billion passwords will take a considerable amount of time. This is in contrast to more traditional hash functions such as MD5 or the SHA family which can be implemented extremely fast on cheap hardware.
Installation
$ hg clone http://bitbucket.org/mhallin/py-scrypt $ cd py-scrypt $ python setup.py build
Become superuser (or use virtualenv): # python setup.py install
Run tests after install: $ python tests/scrypt-tests.py
If you want py-scrypt for your Python 3 environment, just run the above commands with your Python 3 interpreter. Py-scrypt supports both Python 2 and 3.
Usage
The bindings are very simple – there is an encrypt and a decrypt method on the scrypt module:
>>> import scrypt
>>> data = scrypt.encrypt('a secret message', 'password', maxtime=0.1) # This will take at least 0.1 seconds
>>> data[:20]
'scrypt\x00\r\x00\x00\x00\x08\x00\x00\x00\x01RX9H'
>>> scrypt.decrypt(data, 'password', maxtime=0.1) # This will also take at least 0.1 seconds
'a secret message'
>>> scrypt.decrypt(data, 'password', maxtime=0.05) # scrypt won't be able to decrypt this data fast enough
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
scrypt.error: decrypting file would take too long
>>> scrypt.decrypt(data, 'wrong password', maxtime=0.1) # scrypt will throw an exception if the password is incorrect
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
scrypt.error: password is incorrect
From these, one can make a simple password verifier using the following functions:
- def randstr(length):
return ‘’.join(chr(random.randint(0,255)) for i in range(length))
- def hash_password(password, maxtime=0.5, datalength=64):
return scrypt.encrypt(randstr(datalength), password, maxtime=maxtime)
- def verify_password(hashed_password, guessed_password, maxtime=0.5):
- try:
scrypt.decrypt(hashed_password, guessed_password, maxtime) return True
- except scrypt.error:
return False
Acknowledgements
[Scrypt][] was created by Colin Percival and is licensed as 2-clause BSD. Since scrypt does not normally build as a shared library, I have included the source for the currently latest version of the library in this repository. When a new version arrives, I will update these sources.
[Burstaholic][] on Bitbucket provided the necessary changes to make the library build on Windows.
License
This library is licensed under the same license as scrypt; 2-clause BSD.
[scrypt]: http://www.tarsnap.com/scrypt.html [Python]: http://python.org [Burstaholic]: https://bitbucket.org/Burstaholic
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