Proximity check for communication devices
There is described a method of checking whether a transponder device ( 220 ) is in proximity of a reader device ( 210 ), the method comprising (a) transmitting a first command ( 331 ) from the reader device to the transponder device, (b) in response to receiving the first command at the transponder device, transmitting a first response ( 332 ) to the reader device, the first response including an expected transponder device response time (pubRespTime) which is stored in a memory ( 224 ) of the transponder device, (c) transmitting a second command ( 333 ) from the reader device to the transponder device, (d) in response to receiving the second command at the transponder device, transmitting a second response ( 334 ) to the reader device, (e) at the reader device, determining the transponder device response time as the difference in time between transmitting the second command and receiving the second response from the transponder device, and (f) determining whether the determined transponder device response time matches the expected transponder device response time included in the first response. There is also described a reader device ( 210 ), a transponder device ( 220 ), and a contactless communication system ( 200 ).
1. A method of checking whether a transponder device is in proximity of a reader device, the method comprising:
transmitting a first command from the reader device to the transponder device;
in response to receiving the first command at the transponder device, transmitting a first response to the reader device, the first response including an expected transponder device response time (pubRespTime);
determining an actual transponder device response time;
determining whether the determined actual transponder device response time fulfills a predetermined criterion relative to the expected transponder device response time included in the first response; and
verifying a proximity check by comparing a message authentication code (MAC) calculated based at least on the expected transponder device response time with a received MAC.
2. The method according to claim 1 , further comprising:
transmitting a second command from the reader device to the transponder device; and
in response to receiving the second command at the transponder device, transmitting a second response to the reader device, wherein the step of determining the actual transponder device response time comprises determining a difference in time between transmitting the second command from the reader device and receiving the second response at the reader device.
3. The method according to claim 2 , wherein the second command comprises at least a part (pRndC) of a random challenge (RndC), the second response comprises at least a part (pRndR) of a response (RndR) to the random challenge (RndC), and the step of transmitting the second command and the step of transmitting the second response are repeated until the complete random challenge (RndC) and the complete response (RndR) to the random challenge have been transmitted.
4. The method according to claim 1 , further comprising:
transmitting a third command from the reader device to the transponder device, the third command comprising a reader MAC based at least on the expected transponder device response time included in the first response;
in response to receiving the third command at the transponder device: calculating an expected reader MAC based on the third command, verifying that the expected reader MAC equals the reader MAC comprised in the third command, and transmitting a third response to the reader device, the third response comprising a transponder MAC based at least on the expected transponder device response time of the transponder device; and
in response to receiving the third response at the reader device: calculating an expected transponder MAC based on the third response, and verifying that the expected transponder MAC equals the transponder MAC comprised in the third response.
5. The method according to claim 1 , wherein the expected transponder device response time is stored in a memory of the transponder device, and the expected transponder device response time is calculated upon receipt of the first command based on at least one parameter representative of a current state of the transponder device.
6. The method according to claim 1 , wherein the predetermined criterion is fulfilled if the actual transponder device response time does not exceed the expected transponder device response time by a predetermined amount.
7. A reader device for contactless communication with a transponder device, the reader device comprising:
an antenna;
a memory; and
a processing unit, wherein the processing unit is configured to transmit a first command to the transponder device, receive a first response from the transponder device, the first response including an expected transponder device response (pubRespTime), determine an actual response time of the transponder device, determine whether the determined actual transponder device response time fulfills a predetermined criterion relative to the expected transponder device response time included in the first response, and verify a proximity check by comparing a message authentication code (MAC) calculated based at least on the expected transponder device response time with a received MAC.
8. The reader device according to claim 7 , wherein the processing unit is further configured to transmit a second command to the transponder device, receive a second response from the transponder device, and determine the actual transponder response time by determining a difference in time between transmitting the second command and receiving the second response.
9. The reader device according to claim 7 , wherein the second command comprises at least a part (pRndC) of a random challenge (RndC), the second response comprises at least a part (pRndR) of a response (RndR) to the random challenge (RndC), and the processing unit is configured to repeatedly transmit the second command and repeatedly receive the second response until the complete random challenge (RndC) has been transmitted and the complete response (RndR) to the random challenge (RndC) has been received.
10. The reader device according to claim 7 , wherein the processing unit is further configured to transmit a third command to the transponder device, the third command comprising a reader MAC based at least on the expected transponder device response time included in the first response, receive a third response from the transponder device, the third response comprising a transponder MAC based at least on the expected transponder device response time of the transponder device, calculate an expected transponder MAC based on the third response, and verify that the expected transponder MAC equals the transponder MAC comprised in the third response.
11. The reader device according to claim 7 , wherein the predetermined criterion is fulfilled if the actual transponder device response time does not exceed the expected transponder device response time by a predetermined amount.
12. A transponder device for communication with a reader device, the transponder device comprising:
an antenna;
a memory; and
a processing unit, wherein the processing unit is configured to receive a first command from the reader device, and transmit a first response to the reader device, the first response including an expected transponder device response time (pubRespTime), such that the reader device may check whether the transponder device is in proximity of the reader device by determining whether the actual transponder device response time fulfills a predetermined criterion relative to the expected transponder device response time included in the first response and verify a proximity check by comparing a message authentication code (MAC) calculated based at least on the expected transponder device response time with a received MAC.
13. The transponder device according to claim 12 , wherein the processing unit is further configured to receive a second command from the reader device, the second command comprising at least a part (pRndC) of a random challenge (RndC), and transmit a second response to the reader device, the second response comprising at least a part (pRndR) of a response (RndR) to the random challenge (RndC), wherein the processing unit is configured to repeatedly receive the second command and repeatedly transmit the second response until the complete random challenge (RndC) has been received and the complete response (RndR) to the random challenge (RndC) has been transmitted.
14. The transponder device according to claim 12 , wherein the processing unit is further configured to receive a third command from the reader device, the third command comprising a reader MAC based at least on the expected transponder device response time included in the first response, calculate an expected reader MAC based on the third command, verify that the expected reader MAC equals the reader MAC comprised in the third command, and transmit a third response to the reader device, the third response comprising a transponder MAC based at least on the expected transponder device response time of the transponder device.
15. The transponder device according to claim 12 , wherein the expected transponder device response time is stored in a memory of the transponder device, and the processing unit is configured to calculate the expected transponder device response time based on at least one parameter representative of a current state of the transponder device.
16. A communication system, the system comprising
the reader device according to claim 7 , and
a transponder device.