[nmgsd]

I agree strongly with you that the direction to be taken is independent messaging clients for existing messaging channels as long as those channels allow third party API use.

What channel would you use to share the keys on FB? The Facebook API simply will not let you do that anymore. Direct messages have a character limit and you can't just post to someone's wall anymore.

I tried working on something like this for seecret.io but was confounded by the Facebook API's limitations.

Twitter is much better for that. Probably other network too.

[nsajko]

What's the point of encryption if you are going to share the keys via fb? That does not seem better than using a substitution cypher.

[ihm]

You use Diffie–Hellman. "Diffie–Hellman key exchange method allows two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure channel." (https://en.wikipedia.org/wiki/Diffie–Hellman_key_exchange)