Haven't looked into deeply but I just googled "blockchain based encrypted chat" and got this.
 
https://echat.io/
Blockchain-based decentralized secure messenger and fastest-growing social network.

@littleboy The regulations and small barricades to the adaptation of blockchain technology are necessary to have clear rules when all this passes the mountain will continue up, we are going through a process of technology transition good things come, I wish you the best of successes and you I will be following to be attentive to your content, greetings and luck!