i am curious if this would be possible.
i am guessing you could create a contract that issues a key for a decentralised messaging system.
Then one party sends a coin to a second party with whom they wish to communicate using the encrypted system. The sent coin effectively becomes a coloured coin. The second party sends the coin to the contract which recognises the coin as being initially sent by the first party and issues a key allowing the second party to access encrypted messages from the first party.
Would this be a good use of ethereum? It would dispense with the need to have a centralised encryption service such as silent circle.