Method and system for veryfying the authenticity of a first communication participants in a communications network

A method of checking authenticity of a first communication subscriber in a communication network having first and second communication subscribers, comprising:

• forming a first error detection datum at the first communication subscriber;
• transmitting an information item concerning a random datum from the first communication subscriber to the second communication subscriber;
• forming a second error detection datum of the second communication subscriber;
• forming an error information item at the second communication subscriber, using the second error detection datum and the information item concerning the random datum;
• transmitting the error information item from the second communication subscriber to the first communication subscriber;
• and
• checking the first and second error detection data at the first communication subscriber using the error information item.