View Source Pbkdf2 (pbkdf2_elixir v2.3.0)

Elixir wrapper for the Pbkdf2 password hashing function.

For a lower-level API, see Pbkdf2.Base.

Configuration

The following parameter can be set in the config file:

:rounds - computational cost
- the number of rounds
- 160_000 is the default

If you are hashing passwords in your tests, it can be useful to add the following to the config/test.exs file:

# Note: Do not use this value in production
config :pbkdf2_elixir,
  rounds: 1

Pbkdf2

Pbkdf2 is a password-based key derivation function that uses a password, a variable-length salt and an iteration count and applies a pseudorandom function to these to produce a key.

The original implementation used SHA-1 as the pseudorandom function, but this version uses HMAC-SHA-512, the default, or HMAC-SHA-256.

Warning

It is recommended that you set a maximum length for the password when using Pbkdf2. This maximum length should not prevent valid users from setting long passwords. It is instead needed to combat denial-of-service attacks. As an example, Django sets the maximum length to 4096 bytes. For more information, see this link.

Summary

Functions

hash_pwd_salt(password, opts \\ [])

Hashes a password with a randomly generated salt.

no_user_verify(opts \\ [])

Runs the password hash function, but always returns false.

verify_pass(password, stored_hash)

Verifies a password by hashing the password and comparing the hashed value with a stored hash.

Functions

hash_pwd_salt(password, opts \\ [])

Hashes a password with a randomly generated salt.

Options

In addition to the options for Pbkdf2.Base.gen_salt/1 (:salt_len and :format), this function also takes options that are then passed on to the hash_password function in the Pbkdf2.Base module.

See the documentation for Pbkdf2.Base.hash_password/3 for further details.

Examples

The following examples show how to hash a password with a randomly-generated salt and then verify a password:

iex> hash = Pbkdf2.hash_pwd_salt("password")
...> Pbkdf2.verify_pass("password", hash)
true

iex> hash = Pbkdf2.hash_pwd_salt("password")
...> Pbkdf2.verify_pass("incorrect", hash)
false

The next examples show how to use some of the various available options:

iex> hash = Pbkdf2.hash_pwd_salt("password", rounds: 100_000)
...> Pbkdf2.verify_pass("password", hash)
true

iex> hash = Pbkdf2.hash_pwd_salt("password", digest: :sha256)
...> Pbkdf2.verify_pass("password", hash)
true

iex> hash = Pbkdf2.hash_pwd_salt("password", digest: :sha256, format: :django)
...> Pbkdf2.verify_pass("password", hash)
true

no_user_verify(opts \\ [])

Runs the password hash function, but always returns false.

This function is intended to make it more difficult for any potential attacker to find valid usernames by using timing attacks. This function is only useful if it is used as part of a policy of hiding usernames.

There are concerns about this function using too many resources (CPU and memory). An alternative approach is to create a function that adds a sleep calculated to make the time spent running the function the same as if the hash function was run.

Options

This function should be called with the same options as those used by hash_pwd_salt/2.

verify_pass(password, stored_hash)

Verifies a password by hashing the password and comparing the hashed value with a stored hash.

See the documentation for hash_pwd_salt/2 for examples of using this function.