OpenSSL 1.0.1c with updates to compile for Windows Phone 8. The Visual Studio projects can be found under openssl-1.0.1c/vsbuild.
A Windows Phone Runtime Component class can be found under openssl-1.0.1c/vsbuild/OpenSSLWP8. It includes both a client a server example.
This was based on a StackOverflow answer from Oliver Ciappara.
Parts of the OpenSSL source has been modified to compile against Windows Phone 8. Review the commits before using this code in production! This project was just a proof of concept to show that OpenSSL could be used.