Quite a few of the openssl functions require a key or a certificate parameter. Following methods may be used to get them:
Certificates
OpenSSL X.509)
        returned from openssl_x509_read()
       
      Certificate Signing Requests (CSRs)
OpenSSL X.509 CSR)
        returned from openssl_csr_new()
       
      Public/Private Keys
OpenSSL key)
        returned from openssl_get_publickey() or
        openssl_get_privatekey()
       
      OpenSSL X.509)
       
      array($key, $passphrase) where $key represents a
        key specified using the file:// or textual content notation above, and
        $passphrase represents a string containing the passphrase for that
        private key