I am searching for a Instant Messenger SDK to integrate it into the software, so that the software will have the chatting function. We mainly use it in company. Through it, we can talk with each other about the business or others important information. The information will be safe through it.
Now there are lots of chatting tools that always can not guarantee the security of the information.

You'll want something with end-to-end encryption.

Telegram is open-source and has an API.
https://telegram.org/

ChatSecure is also worth a mention.
https://chatsecure.org/blog/

Thanks for your recommend. I will check them later.

You'll want something with end-to-end encryption.

Telegram is open-source and has an API.
https://telegram.org/

ChatSecure is also worth a mention.
https://chatsecure.org/blog/

Are you a software developer? Ijust have a recommend for you. Yunmai Instant Messenger SDK may be the one you want.
http://www.yunmai.com/en/ocr_sdks/instant_messenger.html