Comeonin.Bcrypt
Module to handle bcrypt authentication.
Bcrypt is a key derivation function for passwords designed by Niels Provos and David Mazières. Bcrypt is an adaptive function, which means that it can be configured to remain slow and resistant to brute-force attacks even as computational power increases.
This bcrypt implementation is based on the latest OpenBSD version, which fixed a small issue that affected some passwords longer than 72 characters.
The computationally intensive code is run in C, using Erlang NIFs. One concern about NIFs is that they block the Erlang VM, and so it is better to make sure these functions do not run for too long. This bcrypt implementation has been adapted so that each NIF runs for as short a time as possible.
Summary↑
| bf_encrypt(state) | Encrypt and return the hash |
| bf_expand(state, key, key_len, salt) | The main key expansion function. This function is called 2^log_rounds times |
| bf_init(key, key_len, salt) | Initialize the P-box and S-box tables with the digits of Pi, and then start the key expansion process |
| checkpw(password, hash) | Check the password |
| dummy_checkpw() | Perform a dummy check for a user that does not exist. This always returns false. The reason for implementing this check is in order to make user enumeration by timing responses more difficult |
| gen_salt() | |
| gen_salt(log_rounds) | Generate a salt for use with the |
| hashpass(password, salt) | Hash the password using bcrypt |
| hashpwsalt(password) | Hash the password with a salt which is randomly generated |
| init() |
Functions
Encrypt and return the hash.
The main key expansion function. This function is called 2^log_rounds times.
Initialize the P-box and S-box tables with the digits of Pi, and then start the key expansion process.
Check the password.
The check is performed in constant time to avoid timing attacks.
Perform a dummy check for a user that does not exist. This always returns false. The reason for implementing this check is in order to make user enumeration by timing responses more difficult.
Generate a salt for use with the hashpass function.
The log_rounds parameter determines the computational complexity of the generation of the password hash. Its default is 12, the minimum is 4, and the maximum is 31.
Hash the password using bcrypt.
Hash the password with a salt which is randomly generated.
To change the complexity (and the time taken) of the password hash
calculation, you need to change the value for bcrypt_log_rounds
in the config file.