readme.md

SRTP decoder decodes WebRTC media streams and writes decoded payload into the file

This tool:

• decodes pcap (Packet Capture) format
• extracts RTP packets
• filters packets by SSRC
• decodes secure
• write payload to output file

RTP can be packed in different way.
Supports stream: WebRTC, Regular SRTP, Turn Extensions.

To store opus packets in a file, you need some kind of container format that stores the packet boundaries. I am using https://www.opus-codec.org simple container format.
Option: container[true/false] - switches on/off this feature.

Usage:

srtp_decoder[.exe] input output ssrc key sha container

• input - input pcap file path (Not pcapng!!!, just pcap)
• output - output pcm file path
• ssrc - RTP stream identifier https://tools.ietf.org/html/rfc3550#page-59 hex with 0x prefix
• sha - crypto suite name https://tools.ietf.org/html/rfc4568#page-16
• container - true/false see feature description above

Compiling:

Linux/MAC

git clone https://github.com/ogolosovskiy/srtp_decoder.git
cd srtp_decoder
mkdir build
cd build
cmake ..
make
export PATH=`pwd`:"$PATH"

Windows (Visual Studio Community 2013)

./win32/srtp_decoder.sln

Prerequrements linux/mac

install libsrtp (https://github.com/dozeo/libsrtp I recomend)
install libpcap

Prerequrements windows

setup include/lib path to
libsrtp https://github.com/cisco/libsrtp
winpcap https://www.winpcap.org/devel.htm

How to play pcm

http://www.audacityteam.org/
File->Import->Raw data-> A-Law:Little-Endian:1 Channel(Mono):0:100:8000Hz

How to play OPUS

https://www.opus-codec.org
curl http://downloads.xiph.org/releases/opus/opus-1.1.3.tar.gz -o opus.tar.gz
tar -xvf ./opus.tar.gz
cd opus-1.1.3/
./configure
make
use opus_demo for converting OPUS payload to PCM
./opus_demo -d 48000 1 payloadfile pcmfile
play it by audacity
File->Import->Raw data-> PCM 16 bit 48000Hz

SDES/DTLS srtp

TO DO How to extract SEDS key/crypto from SDP
TO DO How to extract DTLS key/crypto from browser logs