The invention relates to a method for transmitting data between a GRPS/EDGE radio access network and user equipment of a mobile system, and to user equipment using the method, and to GERAN. In the method, the data to be transmitted is encrypted using an encryption algorithm at the transmitting end, the encrypted data is transmitted from the transmitting end to the receiving end, and the transmitted data is decrypted using an encryption algorithm at the receiving end. The used encryption algorithm is an encryption algorithm of the radio access network UTRAN employing the wideband code division multiple access method of the universal mobile telecommunications system, in which case the input parameters of agreed format required by the encryption algorithm are created on the basis of the operating parameters of the GPRS/EDGE radio access network GERAN.