Abstract: 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 (5) to the third computer system (16). A third message is sent from the first 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 identities of the subjects who operates the first and second computer systems thus guarantying the identity of the subjects, the confidentiality of the data transmitted and the reliability of the transmission.