The invention relates to a method for authenticating and/or identifying a device, a service, a person and/or money in a communication network, consisting of a first communication device and an additional communication device, for example a central database, between which an authentication query is carried out. Initially, a first key is provided in the communication device, which comprises at least one character sequence consisting of individual or several locally modifiable characters which can be dynamically modified in accordance with a measurable variable or an algorithm which is dependent on the measurable variable, rules and/or instructions in the communication device, between two authentication time points. A second key is also provided in the central database or an additional communication subscriber which comprises a character sequence consisting of centrally modifiable characters and optionally non-modifiable characters. In a further step, a transmission and a comparison of the key stored in the central database and the communication device is carried out.