Abstract: A method for conducting transaction between first user and a remote second user interlinked through a communication network, by utilizing also a clearing office interlinked to the network. The clearing office storing the user privileged information. The method including the steps of the user and the clearing office establishing a cryptographic secured session, the user transmitting, via the session, a user privileged information and transaction specific data, the transaction specific data being indicative of a transaction identification data. The clearing office activating transaction validity checking procedure by utilizing a user privileged information and the transaction specific data. In response to affirmative result of the transaction validity checking, the clearing office producing a transaction validity indication being indicative of the transaction identification code.