The article links to https://www.4armed.com/blog/hacking-team-rcs-analysis-hacked-team https://www.4armed.com/blog/hacking-team-rcs-analysis-hacked... which has

The article links to https://www.4armed.com/blog/hacking-team-rcs-analysis-hacked-team https://www.4armed.com/blog/hacking-team-rcs-analysis-hacked... which has a detailed analysis of RCS including source code.