techniques for increasing is secure against manipulation in a bi-directional, wireless data transmission

摘要

Fixed relationship is created, i.e. frequency of signal received by transponder is multiplied by number and then sent back to base unit. At base unit, returned signal frequency is divided by same number. Frequency value of original transmitted signal and returned signal are compared, if comparison value is below predetermined limit, there is fixed frequency relationship between them, so no lengthening of communication path by radio amplifiers has occurred. Procedure to increase manipulation security for bidirectional contactless data transfer e.g. between key ring transponder and car door lock. Fixed relationship is created between selected physical size of electromagnetic signal (fULmod), e.g. the frequency of signal received by transponder is multiplied by a number and then sent back (f'DLmod) to the base unit. At the base unit the frequency of the returned signal (f''DLmod) is divided by the same number. Then the frequency value of the original transmitted signal and the returned signal is compared, if the comparison value (CL) is below a predetermined limit, there is a fixed frequency relationship between the two signals and so a lengthening of the communication path by radio amplifiers has not occurred and further authorization is allowed.