def CURVE_client!(client_cert, server_cert)
      if server_cert.secret_key
        raise SecurityError, "server's secret key not secret"
      end

      client_cert.apply(self) # NOTE: desired: raises if no secret key in cert
      options.CURVE_serverkey = server_cert.public_key
    end
def CURVE_client!(client_cert, server_cert)
      if server_cert.secret_key
        raise SecurityError, "server's secret key not secret"
      end

      client_cert.apply(self) # NOTE: desired: raises if no secret key in cert
      options.CURVE_serverkey = server_cert.public_key
    end
Enables CURVE security and makes this socket a CURVE client.
 @param client_cert [Certificate] client's certificate, to secure
   communication (and be authenticated by the server)
 @param server_cert [Certificate] the remote server's certificate, so
   this socket is able to authenticate the server
 @return [void]
 @raise [SecurityError] if the server's secret key is set in server_cert,
   which means it's not secret anymore
 @raise [SystemCallError] if there's no secret key in client_cert