ExDTLS

DTLS and DTLS-SRTP handshake library for Elixir, based on OpenSSL.

ExDTLS allows a user to perform DTLS handshake (including DTLS-SRTP one) without requiring any socket. Instead, it generates DTLS packets that a user has to transport to the peer. Thanks to this DTLS handshake can be performed on the third-party socket e.g. one used to establish a connection via ICE protocol.

Installation

The package can be installed by adding ex_dtls to your list of dependencies in mix.exs:

def deps do
  [
    {:ex_dtls, "~> 0.15.0"}
  ]
end

Usage

ExDTLS uses OpenSSL under the hood. Make sure you have it installed on your OS.

Init ExDTLS on both peers with:

# One peer should be a client (use `mode: :client`) and the other 
# one a server (use `mode: :server`). 
# DTLS-SRTP is the most common use case for ExDTLS, we'll enable it.
dtls = ExDTLS.init(mode: :client, dtls_srtp: true)

On a peer running in a client mode start performing DTLS handshake

{packets, timeout} = ExDTLS.do_handshake(dtls)

You will obtain initial handshake packets and a timeout. packets has to be passed to the second peer (using your own socket UDP). timeout is a time after which ExDTLS.handle_timeout/1 should be called.

After receiving initial DTLS packets on the second peer pass them to ExDTLS:

{:handshake_packets, packets, timeout} = ExDTLS.handle_data(dtls, packets)

As a result, we will also get some new packets that have to be passed to the first peer.

After some back and forth DTLS handshake should be finished successfully. The peer that finishes the handshake first will return {:handshake_finished, local_keying_material, remote_keying_material, protection_profile, packets} tuple. These packets have to be sent to the second peer, so it can finish its handshake too and return {:handshake_finished, local_keying_material, remote_keying_material, protection_profile} tuple.

For more complete examples please refer to ex_webrtc where we use ex_dtls or to our integration tests.