I am very proud to announce, that Smack got support for OpenPGP for XMPP!
Today the Pull Request I worked on during my GSoC project was merged into Smacks master branch. Admittedly it will take a few months until smack-openpgp will be included in a Smack release, but that gives me time to further finalize the code and iron out any bugs that may be in there. If you want to try smack-openpgp for yourself, let me know of any issues you encounter 🙂
(Edit: There are snapshot releases of Smack available for testing)
Now Smack does support two end-to-end encryption methods, which complement each other perfectly. OMEMO is best for people that want to be safe from future attacks, while OpenPGP is more suited for users who appreciate being able to access their chat history at any given time. OpenPGP is therefore the better choice for web based applications, although it is perfectly possible to implement web based clients that do OMEMO (see for example the Wire web app, which does ratcheting similar to OMEMO).
What’s left to do now is updating smack-openpgp due to updates made to XEP-0373 and extensive testing against other implementations.