Comeonin

Comeonin is a password hashing library that aims to make the secure validation of passwords as straightforward as possible.

It also provides extensive documentation to help developers keep their apps secure.

Comeonin supports bcrypt and pbkdf2_sha512.

Use

Import, or alias, the algorithm you want to use — either Comeonin.Bcrypt or Comeonin.Pbkdf2.

To hash a password with the default options:

hash = hashpwsalt("difficult2guess")

See each module’s documentation for more information about all the available options.

If you want more control over the generation of the salt, and, in the case of pbkdf2, the length of salt, you can use the gen_salt function and then pass the output to the hashpass function.

To check a password against the stored hash, use the checkpw function. This takes two arguments: the plaintext password and the stored hash:

checkpw(password, stored_hash)

There is also a dummy_checkpw function, which takes no arguments and is to be used when the username cannot be found. It performs a hash, but then returns false. This can be used to make user enumeration more difficult. If an attacker already knows, or can guess, the username, this function will not be of any use, and so if you are going to use this function, it should be used with a policy of creating usernames that are not made public and are difficult to guess.

Choosing an algorithm

Bcrypt and pbkdf2_sha512 are both highly secure key derivation functions. They have no known vulnerabilities and their algorithms have been used and widely reviewed for at least 10 years. They are also designed to be future-adaptable (see the section below about speed / complexity for more details), and so we do not recommend one over the other.

However, if your application needs to use a hashing function that has been recommended by a recognized standards body, then you will need to use pbkdf2_sha512, which has been recommended by NIST.

Adjusting the speed / complexity of bcrypt and pbkdf2

Both bcrypt and pbkdf2 are designed to be computationally intensive and slow. This limits the number of attempts an attacker can make within a certain time frame. In addition, they can be configured to run slower, which can help offset some of the hardware improvements made over time.

It is recommended to make the key derivation function as slow as the user can tolerate. The actual recommended time for the function will vary depending on the nature of the application. According to the following NIST recommendations (http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf), having the function take several seconds might be acceptable if the user only has to login once every session. However, if an application requires the user to login several times an hour, it would probably be better to limit the hashing function to about 250 milliseconds.

To help you decide how slow to make the function, this module provides convenience timing functions for bcrypt and pbkdf2.