Client-side encryption of messages across apps Is it possible to encrypt any message (part) across apps?

I'd want


client-side encryption
using pgp keys (asymmetric public/secret)
integrate into multiple apps (like WhatsApp, GoogleTalk, ...), independent of their support
integration via some kind of overlay box
apps would send pgp encrypted block, recipient would then read decrypted (after inserting pass-phrase)
pass-phrase to secret key could be remembered / empty (for seamless/more comfortable decrypting)


does anybody know of such an app?

Motivation:

I want to be able to encrypt messages, but don't want (to have) to convince messaging partners to switch to just another messaging app just for me. Instead we'd both install the encryption overlay and would have a trustworthy chat. With people not using encryption I still could communicate via the same app.
No. Apps on Android can't interfere with each other's operations to the extent you describe. I can think of two options that come close to what you describe:


Use a standard PGP app and copy-and-paste ciphertext between that and the chat app.
If the chat app you're using uses direct client-to-client transmissions, instead of every message going via a server, then you could set up a VPN and ask your partner to join it before starting to chat with you.


To be honest, neither of these options, nor the ideal circumstance you describe, sound like an easier sell than simply asking your friends to use a secure chat system. I suggest to you that Jabber offers this functionality while allowing a choice of clients, some of which can also use different chat systems, so it might be the easiest transition path.