As of this writing, wolfSSL, which is our small embedded SSL library, supports all of the most commonly used OpenSSL functions. As time goes on, we are incrementally improving our OpenSSL compatibility.
Our process for improvement is driven by two forces.
Firstly, we respond to customer requirements. Our customers migrate from OpenSSL to wolfSSL for a variety of reasons. Some migrate to get support for a particular RTOS or embedded environment not supported by OpenSSL. Others need to reduce the overall size of their application by using a smaller library. There are also some that migrate because they are seeking commercial licensing and professional support.
Secondly, we test the compatibility layer by building wolfSSL with other open source projects that currently use OpenSSL. We simply see what breaks, and then we add the missing OpenSSL functions to fix it. You can see a couple of these efforts available on our download page in the form of experimental versions of Lighttpd and Stunnel. Contact us if you would like help compiling wolfSSL with Lighttpd or stunnel. We’ll be happy to help!