Shhlack, message encryption for Slack
In Summary : Shhlack is not a Slack bot. Instead it injects itself in the Slack web UI and uses Slack internal client APIs to encrypt/dec...
https://updatesinfosec.blogspot.com/2018/05/shhlack-message-encryption-for-slack.html

Shhlack is not a Slack bot. Instead it injects itself in the Slack web UI and uses Slack internal client APIs to encrypt/decrypt messages on the fly by choosing a passphrase from a set of stored keys owned by the user using cryptojs.AES JS library[...]
kindly refer the following link as follow up :
https://ift.tt/2I3eQDX