Well, most of the credit goes to the friendly dutch guy who wrote a library for the Threema communication protocol:
The Threema protocol is not open source, but on request Threema allowed a smart student to reverse engineer the protocol. Based on his work the OpenMittsu desktop client was developed (by some other guy).
Mister Bruintjes went ahead and developed not only a cool C++ based library that manages communication with the Threema servers, but he also developed a libpurple based plugin (threepl). threepl works out of the box within Pidgin, so I thought it can’t be hard to make it work in Chatty, since it supports libpurple based plugins.
Basic communication is working (text and emoticons), but there is still a lot missing (the handshake necessary to indicate status (sent, received, seen etc.) is not integrated into libpurple and must be added in Chatty itself).
It is completely independent of “Threema Web”. I added my account and my contacts within Chatty itself.
Unfortunately I do not have a lot of time to put into the details still missing, but over time the integration will get better and better (I hope). I have not made a pull request of my changes to the repository yet, so there is no way for you to test this so far.
Thanks again for all the constructive posts in this forum, @Caliga.
Cheers,
orrence.