Salt and hash a password in python

Question

This code is supposed to hash a password with a salt. The salt and hashed password are being saved in the database. The password itself is not.

Given the sensitive nature of the operation, I wanted to make sure everything was kosher.

Note: I use the url safe version of b64encode out of habit.

import hashlib
import base64
import uuid

password = 'test_password'
salt     = base64.urlsafe_b64encode(uuid.uuid4().bytes)


t_sha = hashlib.sha512()
t_sha.update(password+salt)
hashed_password =  base64.urlsafe_b64encode(t_sha.digest())

Answer 1

The smart thing is not to write the crypto yourself but to use something like passlib: https://bitbucket.org/ecollins/passlib/wiki/Home

It is easy to mess up writing your crypto code in a secure way. The nasty thing is that with non crypto code you often immediately notice it when it is not working since your program crashes. While with crypto code you often only find out after it is to late and your data has been compromised. Therefor I think it is better to use a package written by someone else who is knowledgable about the subject and which is based on battle tested protocols.

Also passlib has some nice features which make it easy to use and also easy to upgrade to a newer password hashing protocol if an old protocol turns out to be broken.

Also just a single round of sha512 is more vulnerable to dictionary attacks. sha512 is designed to be fast and this is actually a bad thing when trying to store passwords securely. Other people have thought long and hard about all this sort issues so you better take advantage of this.

Answer 2

EDIT: This answer is wrong. Don't use a cryptographic hash to store passwords. Use a password hash.

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Looks fine by me. However, I'm pretty sure you don't actually need base64. You could just do this:

import hashlib, uuid
salt = uuid.uuid4().hex
hashed_password = hashlib.sha512(password + salt).hexdigest()

If it doesn't create difficulties, you can get slightly more efficient storage in your database by storing the salt and hashed password as raw bytes rather than hex strings. To do so, replace hex with bytes and hexdigest with digest.

Answer 3

For this to work in Python 3 you'll need to UTF-8 encode for example:

hashed_password = hashlib.sha512(password.encode('utf-8') + salt.encode('utf-8')).hexdigest()

Otherwise you'll get:

Traceback (most recent call last):
File "", line 1, in
hashed_password = hashlib.sha512(password + salt).hexdigest()
TypeError: Unicode-objects must be encoded before hashing

Answer 4

passlib seems to be useful if you need to use hashes stored by an existing system. If you have control of the format, use a modern hash like bcrypt or scrypt. At this time, bcrypt seems to be much easier to use from python.

passlib supports bcrypt, and it recommends installing py-bcrypt as a backend: http://pythonhosted.org/passlib/lib/passlib.hash.bcrypt.html

You could also use py-bcrypt directly if you don't want to install passlib. The readme has examples of basic use.

see also: How to use scrypt to generate hash for password and salt in Python

Answer 5

I don' want to resurrect an old thread, but... anyone who wants to use a modern up to date secure solution, use argon2.

https://pypi.python.org/pypi/argon2_cffi

It won the the password hashing competition. ( https://password-hashing.net/ ) It is easier to use than bcrypt, and it is more secure than bcrypt.

Answer 6

Based on the other answers to this question, I've implemented a new approach using bcrypt.

Why use bcrypt

If I understand correctly, the argument to use bcrypt over SHA512 is that bcrypt is designed to be slow. bcrypt also has an option to adjust how slow you want it to be when generating the hashed password for the first time:

# The '12' is the number the dictates the 'slowness'
bcrypt.hashpw(password, bcrypt.gensalt( 12 ))

Slow is desirable because if a malicious party gets their hands on the table containing hashed passwords, then it is much more difficult to de-encrypt them.

Implementation

def get_hashed_password(plain_text_password):
    # Hash a password for the first time
    #   (Using bcrypt, the salt is saved into the hash itself)
    return bcrypt.hashpw(plain_text_password, bcrypt.gensalt())

def check_password(plain_text_password, hashed_password):
    # Check hased password. Useing bcrypt, the salt is saved into the hash itself
    return bcrypt.checkpw(plain_text_password, hashed_password)

Notes

I was able to install the library pretty easily in a linux system using:

pip install py-bcrypt

However, I had more trouble installing it on my windows systems. It appears to need a patch. See this Stackoverflow question: py-bcrypt installing on win 7 64bit python