Provides a simple Hashed Message Authentication Code (HMAC)-based
key derivation function (HKDF).

Based on the algorithm defined in [rfc 5859](

## Usage

Derive key:
HKDF.derive(:sha256, "some input", 42, "optional salt", "optional secret message")

Expand pseudorandom key:
HKDF.extract(:sha256, "some input", "optional salt")

Extract output key material:
prk = HKDF.extract(:sha256, "some input", "optional salt")
HKDF.expand(:sha256, prk, 16, "optional secret message")

## Installation

If [available in Hex](, the package can be installed
by adding `hkdf` to your list of dependencies in `mix.exs`:

def deps do
  [{:hkdf, "~> 0.2.0"}]

Documentation can be generated with [ExDoc](
and published on [HexDocs]( Once published, the docs can
be found at [](