#53 Per-resource handling of encryption availability

[asmundg]

Pidgin-Encryption misbehaves when a contact uses multiple resources, of which only some have the Pidgin-Encryption plugin.

When a contact uses pidgin with Pidgin-Encryption on their laptop and a different XMPP client without Pidgin-Encryption support on their cell phone, Pidgin-Encryption appears to assume that all messages to that contact, regardless of the active resource, can be encrypted.

Pidgin-Encryption should be able to disable encryption if sending messages to a contact that does not support encryption. To preserve confidentiality, the user should possibly have to confirm the removal of encryption before sending.