A method and apparatus wherein, for a network protocol a message is encoded in a first computer unit upon employment of the encoding format of the network protocol, being encoded to form an encoded message. The encoded message is subjected to a cryptographic process. The cryptographically processed message thereby formed is again encoded upon employment of the encoding format of the network protocol. The cryptographically processed message encoded in this way is transmitted from the first computer unit to the second computer unit. In the second computer unit, the received message is decoded according to the encoding format of the network protocol, and an inverse cryptographic process is applied to the decoded message. The inversely cryptographically processed message is again decoded according to the encoding format of the network protocol.