Most comprehensive OpenSSL module in the Lua universe.
$ luarocks install luaossl
luaossl is a comprehensive binding to OpenSSL for Lua 5.1, 5.2, and later. I dare say it's the most comprehensive OpenSSL binding in the Lua universe, and one of the most comprehensive bindings of OpenSSL in any language, on par with the best bindings in Python and Ruby. If you think otherwise, let me know so I can fix it!
It includes support for certificate and key management, key generation, signature verification, and deep bindings to the distinguished name, alternative name, and X.509v3 extension interfaces.
It also binds OpenSSL's bignum, message digest, HMAC, cipher, and CSPRNG interfaces. The end goal is to bind almost everything that OpenSSL supports, but no more. It's intended as a low-level interface.