python - What is the format in which Django passwords are stored in the database?

Question

You know how django passwords are stored like this:

sha1$a1976$a36cc8cbf81742a8fb52e221aaeab48ed7f58ab4

and that is the "hashtype $salt $hash". My question is, how do they get the $hash? Is it the password and salt combined and then hashed or is something else entirely?

Answer 1

As always, use the source:

# root/django/trunk/django/contrib/auth/models.py
# snip
def get_hexdigest(algorithm, salt, raw_password):
    """
    Returns a string of the hexdigest of the given plaintext password and salt
    using the given algorithm ('md5', 'sha1' or 'crypt').
    """
    raw_password, salt = smart_str(raw_password), smart_str(salt)
    if algorithm == 'crypt':
        try:
            import crypt
        except ImportError:
            raise ValueError('"crypt" password algorithm not supported in this environment')
        return crypt.crypt(raw_password, salt)

    if algorithm == 'md5':
        return md5_constructor(salt + raw_password).hexdigest()
    elif algorithm == 'sha1':
        return sha_constructor(salt + raw_password).hexdigest()
    raise ValueError("Got unknown password algorithm type in password.")

As we can see, the password digests are made by concatenating the salt with the password using the selected hashing algorithm. then the algorithm name, the original salt, and password hash are concatenated, separated by "$"s to form the digest.

# Also from root/django/trunk/django/contrib/auth/models.py
def check_password(raw_password, enc_password):
    """
    Returns a boolean of whether the raw_password was correct. Handles
    encryption formats behind the scenes.
    """
    algo, salt, hsh = enc_password.split('$')
    return hsh == get_hexdigest(algo, salt, raw_password)

To validate passwords django just verifies that the same salt and same password result in the same digest.