The method provides that a session code (K) can be agreed between a first computer unit (U) and a second computer unit (N), without it being possible for any unauthorized third party to gain access to useful information relating to the codes or the identity of the first computer unit (U). This is achieved by embedding the principle of the El-Gamal code interchange in the method, with additional formation of a digital signature via a hash value of the session code (K) which is formed by the first computer unit (U).