Abstract: An apparatus and a method for the identification and encrypting/decrypting of messages permits converting an input message provided as characters, in character-by-character fashion and depending on preceding characters, to form an output message. An address branching network is employed for encrypting/decrypting. The address branching network includes selectable branches that are carriers of encrypting/decrypting characteristics. The selection of such branches is done in a step-by-step selection run through the branching network to convert any specific input message of optional length character-by-character into a specific selection path through the branching network. The output message is formed on the basis of the encrypting/decrypting characteristics from the branches selected on said selection path.