DTLS Examples for OpenSSL

This repository contains examples for DTLS via SCTP and UDP. Each application in src can be used as client or server.

Our examples are developed against the OpenSSL 1.1.x API.

Use OpenSSL Version 1.1.1a or higher.

SCTP/UDP Examples

DTLS Echo Server and Client
This sample includes a multi-threaded echo server and client sending messages over an SCTP/UDP connection encrypted with DTLS.

Usage: dtls_(udp|sctp)_echo [options] [address]
Options:
        -l      message length (default: 100 Bytes)
        -L      local address
        -p      port (default: 23232)
        -n      number of messages to send (default: 5)
        -v      verbose
        -V      very verbose

DTLS Character Generator Server and Client
This sample includes a multi-threaded character generator server and client sending as many messages as possible to each other over an SCTP/UDP connection encrypted with DTLS for a given time. Statistics how many messages have been sent and received and how many got lost are printed at the end.

Usage: dtls_(udp|sctp)_chargen [options] [address]
Options
        -l      message length (default: 100 Bytes)
        -L      local address
        -s      streams (default: 5, sctp only)
        -p      port (default: 23232)
        -t      time to send (default: 10 sec)
        -u      unordered (sctp only)
        -v      verbose
        -V      very verbose

DTLS Discard Server and Client
This sample includes a multi-threaded discard server and client sending messages over an SCTP/UDP connection encrypted with DTLS.

Usage: dtls_(udp|sctp)_discard [options] [address]
Options:
        -l      message length (Default: 100 Bytes)
        -L      local address
        -s      streams (default: 5, sctp only)
        -p      port (default: 23232)
        -t      time to send (Default: 10 sec)
        -u      unordered (sctp only)
        -v      verbose
        -V      very verbose

OS Requirements

FreeBSD

Since FreeBSD 12.0, the built-in OpenSSL version is sufficient to run the UDP examples.
The SCTP examples and older versions of FreeBSD require OpenSSL to be installed via pkg or from scratch.
For FreeBSD 12.0 and 11.2, the OpenSSL 1.1.1 package from pkg is openssl111.

$ pkg install openssl111

Linux (Ubuntu)

The UDP examples should work with recent Linux distributions out-of-the-box. In order to run the SCTP examples, OpenSSL has to be built from scratch with SCTP support.

• Install the SCTP headers.

sudo apt-get install libsctp-dev

• Download the recent OpenSSL version.
  This example has been tested with OpenSSL 1.1.1a and Ubuntu 18.10.
• Configure OpenSSL to include SCTP support and (optionally) set a custom install prefix.
• Build and install OpenSSL.

$ ./config sctp --prefix=$HOME/my-openssl/
$ make
$ make install

In addition to a loaded SCTP module, Linux requires SCTP AUTH support.

$ modprobe sctp
$ sysctl -w net.sctp.auth_enable=1

macOS

If you only want to run the UDP examples, prebuilt OpenSSL binaries can be installed via brew.

$ brew install openssl@1.1

A SCTP enabled OpenSSL version has to be compiled from source, follow the tutorial in the Linux section. Since macOS does not support SCTP out of the box, it is necessary to use the SCTP NKE.

Build the Examples

Before calling make in the src directory, it may be necessary to specify custom library and include paths. This is either done by modifying the Makefile or by providing the path as a command line argument. It is also possible to only build SCTP or UDP examples.

$ make
$ make sctp  # only SCTP examples
$ make udp  # only UDP examples

OpenSSL Certificates

In order to run the example programs, the required server and client certificates should be located in a certs subfolder.

• client-cert.pem
• client-key.pem
• server-cert.pem
• server-key.pem

The following commands create signed certificates for client and server of the samples above.

touch ca-db-index
echo 01 > ca-db-serial

# Certificate Authority
openssl req -nodes -x509 -newkey rsa:2048 -days 365 -keyout ca-key.pem -out ca-cert.pem

# Server Certificate
openssl req -nodes -new -newkey rsa:2048 -keyout server-key.pem -out server.csr

# Sign Server Certificate
openssl ca -config ca.conf -days 365 -in server.csr -out server-cert.pem

# Client Certificate
openssl req -nodes -new -newkey rsa:2048 -keyout client-key.pem -out client.csr

# Sign Client Certificate
openssl ca -config ca.conf -days 365 -in client.csr -out client-cert.pem

You can create your own ca.conf file or use a minimal sample.

Usage with OpenSSL s_client / s_server

The examples are not limited to be used with each other, they may also be used with the built-in OpenSSL application.

The example below starts a SCTP echo server. The client connects via OpenSSL's s_client application and sends input read from stdin to the server. The server echos received messages.

$ dtls_sctp_echo -V -L 127.0.0.1

$ openssl s_client -sctp -dtls -connect 127.0.0.1:23232