&reftitle.required; In order to use the OpenSSL functions you need to install the OpenSSL library. PHP 5 requires at least OpenSSL >= 0.9.6. However later PHP 5 versions have some compilation issues and should be used at least with OpenSSL >= 0.9.8 which is also a minimal version for PHP 7.0. Other versions (PHP >= 7.1.0) require OpenSSL >= 1.0.1. You are strongly encouraged to use the most recent OpenSSL version, otherwise your web server could be vulnerable to attack.

&reftitle.resources; There are 3 resource types defined in the OpenSSL module. The first one is a pkey (public or private key) identifier, the second one is a X509 certificate identifier and the third one is a CSR (certificate signing request) identifier.