Encryption

Taking care that the Compression is implemented in Coccinella, maybe using the library cryptlib [1] and its TCL wrapper cryptkit [2] this feature isn't difficult to implement.

First is needed to implement the Session negotiation [3], and then follow the xep 200 for stanza encryption [4]. The crypt algorithms that we need from cryptlib at a first read are AES128, SHA-256, HMAC-SHA and a Diffie-Hellman implementation.

For the user interface presentation, not sure how to imagine because I've never used this feature in other software before.

Sure that this will be a nice feature.

[1] http://www.digitalsmarties.com/cryptkit/README
[2] http://www.cs.auckland.ac.nz/~pgut001/cryptlib
[3] https://bugs.launchpad.net/coccinella/+bug/153680
[4] http://www.xmpp.org/extensions/xep-0200.html

Your decision but you must be aware of a bug in the current compression library where non 7-bit characters aren't handled correctly. I have a bug entry on this but Launchpad wont list my bugs. Search for "compress" in the tracker.

See: https://bugs.launchpad.net/coccinella/+bug/154217

Support for Simplified Encrypted Session Negotiation would be nice.

URLs:
http://necronomicorp.com/lab/36
http://www.xmpp.org/extensions/xep-0218.html
http://www.xmpp.org/extensions/xep-0217.html

Read this: https://stpeter.im/?p=2214

Related: http://coccinella.im/node/239

XEP-0217 and XEP-0218 have been deferred, implementation is not recommended.

also XEP-0200 is deferred, and implementation is not recommended.

However, there exists this RFC:
http://xmpp.org/rfcs/rfc3923.html
End-to-End Signing and Object Encryption for the Extensible Messaging and Presence Protocol (XMPP)

Which probably should be the way to go.

  Hello!
  Please excuse me for interrupting a constructive conversation, but are you talking about using GPG to have encrypted chats with one's contacts? (Just like Psi, Gajim, Kopete, and probably some other clients do?).
  If this is what you are talking about, than it's a really really useful feature! :) I wanted to suggest such feature by myself, but then I have seen this bug (or feature request) discussion. If somebody implements it, I think I'll be one of the first users to test it and report if something goes wrong.
  By the way, it seems not to be very difficult to make it possible to have the encrypted group chats if there is a possibility to have private chats. For example, I have a pair of keys (public and private), and my friends have these keys either. In such case I can send a message encrypted with a public key to any one (or as many as I wish) of them and they can decrypt my message using our private key. So personally I do not see much difference between encrypting private and group chats.

  I hope this feature will be implemented soon and I believe other users also do. And looking forward to test it! :)

  Regards,
  Vladimir.