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
This module offers the following convenience functions:
- create_hash — check password strength before hashing it
- create_user — update a map with the password hash
See the documentation for each function for more details.
If you do not need this extra functionality, you can hash a password
by using the hashpwsalt function — using 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.
Further information
Visit our wiki (https://github.com/elixircnx/comeonin/wiki) for links to further information about these and related issues.
Summary↑
| create_hash(password, strength \\ true) | This function can be used to check the strength of a password before hashing it. The password is then hashed only if the password is considered strong enough. For more details about password strength, read the documentation for the Comeonin.Password module |
| create_user(user_params, strength \\ true) | This function takes a map with a password in it, removes the password and adds an entry for the password hash. This can be used after collecting user data and before adding it to the database |
| time_bcrypt(log_rounds \\ 12) | A function to help the developer decide how many log_rounds to use when using bcrypt |
| time_pbkdf2(rounds \\ 60000) | A function to help the developer decide how many rounds to use when using pbkdf2 |
Functions
This function can be used to check the strength of a password before hashing it. The password is then hashed only if the password is considered strong enough. For more details about password strength, read the documentation for the Comeonin.Password module.
The default hashing algorithm is bcrypt, but this can be changed by
setting the value of crypto_mod to :pbkdf2 in the config file.
This function takes a map with a password in it, removes the password and adds an entry for the password hash. This can be used after collecting user data and before adding it to the database.
This uses the create_hash function, which can be used to check password
strength before hashing it.
When looking for the password, this function looks for a key which is either named “password” (a string) or :password (an atom). If it does not find either key, it will raise an error.
As with the create_hash function, you can decide not to check password
strength by setting the second argument to false.
Examples
All of the following will work ok:
%{"name" => "fred", "password" => "&m@ng0es"} |> Comeonin.create_user
%{name: "fred", password: "&m@ng0es"} |> Comeonin.create_user
%{name: "fred", password: "123456"} |> Comeonin.create_user(false)The next example will raise an error because the key “password” or :password could not be found:
iex> %{["name"] => "fred", ["password", "password_admin"] => "&m@ng0es"} |> Comeonin.create_user
{:error, ~s(We could not find the password. The password key should be either :password or "password".)}This example will raise an error because the password is not long enough:
iex> %{name: "fred", password: "123456"} |> Comeonin.create_user
{:error, "The password should be at least 8 characters long."}A function to help the developer decide how many log_rounds to use when using bcrypt.
The number of log_rounds can be increased to make the bcrypt hashing function more complex, and slower. The minimum number is 4 and the maximum is 31. The default is 12, but this is not necessarily the recommended number. The ideal number of log_rounds will depend on the nature of your application and the hardware being used.
The bcrypt_log_rounds value can be set in the config file. See the
documentation for Comeonin.Config for more details.
A function to help the developer decide how many rounds to use when using pbkdf2.
The number of rounds can be increased to make the pbkdf2 hashing function slower. The maximum number of rounds is 4294967295. The default is 60_000, but this is not necessarily the recommended number. The ideal number of log_rounds will depend on the nature of your application and the hardware being used.
The pbkdf2_rounds value can be set in the config file. See the
documentation for Comeonin.Config for more details.