crypt.bcrypt- Password hashing
This module implements a password hashing algorithm using blowfish, and compatible to OpenBSD’s bcrypt algorithm (version 2a, 2b).
Don’t use version “2a” for new code. It’s vulnerable. Use version “2b”.
The typical usage of this module is simple enough.
To get a new password hash value (e.g. for a new user), pass the
password string to
bcrypt-hashpw as the only argument:
(bcrypt-hashpw password) ⇒ hashed-string
The routine automatically adds a salt value. The returned hash
string can be stored in the user database. To check if the given
password matches the stored one, pass the
hashed string as the second argument of
check the password.
(bcrypt-hashpw password hashed-string) ⇒ hashed-string
If the given password is correct, the returned value should exactly matches hash-string.
Calculates a hash value of password, using the salt value and parameters included in setting. If setting is omitted, a suitable default settings and random salt value is chosen automatically.
The returned hash value contains the salt value and parameters, and can be used as setting. So, to check the password against existing hash value, just pass the hash value to setting; if the password is correct, the returned hash value should match the one you passed in.
The bcrypt algorithm supports up to 72 octets for the password.
To tweak parameters when you calculate a new hash value,
bcrypt-gensalt below to get the initial setting
Returns a string that contains given parameters and suitable to
pass to the setting argument of
The prefix argument specifies the version/scheme of
password hashing. Currently
$2b$ are supported,
which means the blowfish algorithm compatible to bcrypt.
$2a$ is vulnerable. Use
$2b$ for new code.
If you omit prefix, use
$2b$ for default value.
The count arugment specifies the amount of iterations;
the larger the value is, the more time is required to calculate
the hash value. Note that for the password hashing, taking more
time is actually a good thing, for it works against the dictionary attack.
For normal password checking you need to run the hash routine only
once per login, so it doesn’t matter if the calculation takes a fraction
The bcrypt algorithm iterates
(expt 2 count) times.
The entropy-source argument is a
u8vector to feed
a random bytes. For bcrypt algorithm it must be at least 16 octet long.