Key/Certificate parameters
 
  Quite a few of the openssl functions require a key or a certificate
  parameter. PHP 4.0.5 and earlier have to use a key or certificate
  resource returned by one of the
  openssl_get_xxx() functions.
  Later versions may use one of the following methods:
  
   - 
    
     Certificates
      
      - 
       
        An X.509 resource returned from
        openssl_x509_read()
       
      
- 
       A string having the format
        file://path/to/cert.pem; the named file must
        contain a PEM encoded certificate
       
      
- 
       
        A string containing the content of a certificate, PEM encoded
       
      
 
- 
    
     Public/Private Keys
      
      - 
       A key resource returned from
        openssl_get_publickey() or
        openssl_get_privatekey()
       
      
- 
       For public keys only: an X.509 resource
      
- 
       A string having the format
        file://path/to/file.pem - the named file must
        contain a PEM encoded certificate/private key (it may contain both)
       
      
- 
       
        A string containing the content of a certificate/key, PEM encoded
       
      
- 
       
        For private keys, you may also use the syntax
        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