The method and system of authentication of authorized person and transaction approval principally at the direct debits by means of a mobile communication device (2) is based on the fact that an alphanumerical chain is sent from the mobile communication device (2) into energy passive identifier (3) approached to the mobile communication device (2), the identifier (3) is supplied contact free by electromagnetic field of the mobile communication device (2) while in the identifier the received alphanumerical chain is signed electronically and in such signed alphanumerical chain is sent back into the mobile communication device (2). Payment approval is realized by the correctness approval of the electronically signed alphanumerical chain and by approaching the mobile communication device (2) to the payment terminal (1). The invention enables to use a high level of cryptography security by using a passive identifier (3) which does not demand own energy source.