A method and a system for transmitting data over a communication network (3). At least three computer systems (2, 5, 16) are connected to the communication network (3). A first message (7) is sent from the first computer system (2) to the second computer system (5). A second message is sent from the second computer system (2) to the third computer system (16). The third computer systems compares the contents of the second and third messages received from the first and second computer systems and verify the identifies of the subjects who operates the first and second computer systems thus guarantying the identity of the subjects, the confidentiality of the data tansmitted and the reliability of the transmission.
