Stunnel is a proxy designed to add TLS encryption functionality to existing clients and servers without any changes in the programs' code. Its architecture is optimized for security, portability, and scalability (including load-balancing), making it suitable for large deployments. Stunnel uses the OpenSSL library for cryptography, so it supports whatever cryptographic algorithms are compiled into
![stunnel](https://cdn-ak-scissors.b.st-hatena.com/image/square/68c4feabc396a38ca3741c5f5e5acdb438c9c1cb/height=288;version=1;width=512/https%3A%2F%2Fwww.stunnel.org%2Fimg%2Ftunnel.jpg)