Method to compensate by a server a clock deviation of a card
This invention relates to a method to compensate by a server a clock deviation of a card i by maintaining a time base Tbase (i) synchronized with card i, the method comprising the steps of: receiving at a time TS a dynamic card verification dCVV code value generated by card i; providing a set of at least two dCVV code corresponding to two successive dCVV time periods; if the dCVV code received from card i corresponds to one of the dCVV codes of the provided set but is different from the reference dCVV code, determine the minimum possible timing drift Min_td between the time base maintained by the server for the card and the time base Tbase(i) of the card; updating time base Tbase(i) by addition of a time drift correction equal to the minimum possible time drift Min_td.
1. A method to compensate by a server a clock deviation of a card i by maintaining a time base Tbase(i) synchronized with card i, the method comprising the steps of:
receiving at a time TS a dynamic card verification dCVV code value generated by card i;
providing a set of at least two dCVV code corresponding to two successive dCVV time periods determined using the time base maintained by the server for the card and such that time TS falls within one of these time periods, a time period being defined as a duration and two time boundaries, the dCVV code associated to this period being called reference dCVV code;
if the dCVV code received from card i corresponds to one of the dCVV codes of the provided set but is different from the reference dCVV code, determine the minimum possible timing drift Min_td between the time base maintained by the server for the card and the time base Tbase(i) of the card, said minimum possible timing drift Min_td being deducted from the time difference between the closest time boundary of the period of time identified of the provided set corresponding to the dCVV received from the card and time TS;
updating time base Tbase(i) by addition of a time drift correction equal to the minimum possible time drift Min_td.
2. The method according to claim 1 , wherein the number of dCVV codes in the provided set corresponds to a tolerance window of a predefined number of successive dCVV codes to be included in said set.
3. The method according to claim 2 , wherein the tolerance window comprises three successive dCVV codes centred on the reference dCVV code.
4. The method according to claim 1 , wherein the number of dCVV codes in the provided set is derived from a tolerance window corresponding to a predefined time duration.
5. The method according to claim 1 comprising a step for determining a deviation coefficient DC configured to adapt the update frequency/f card (i) of the time base Tbase(i) maintained by the server for card i, the deviation coefficient DC being derived from the minimum possible time drift Min_td.
6. The method according to claim 5 , wherein the deviation coefficient is determined using the following expression:
D
C
=
1
+
{
Min_td
T
S
-
T
0
}
where T0 represents the initial date or time clock setting of the card, the clock frequency/f card (i) applied to update time base Tbase(i) being updated using the following expression:
f card ( i )=DC× f TAI
where f TAI represents the clock frequency of the server which is taken as a reference.
7. The method according to claim 5 , wherein the deviation coefficient DC is determined using at least two successive time drift estimations Min_td performed by the server for this card and by applying a function on these at least two estimations to reduce bias of estimation.
8. The method according to claim 7 , wherein the function to reduce the bias of estimation is chosen among: an average function, a linearization function based on the method of least squares, a sin(x)/x interpolation.
9. A server configured to compensate a clock deviation of a card i by maintaining a time base Tbase(i) synchronized with card i, the server adapted to implement a method comprising:
receiving at a time TS a dynamic card verification dCVV code value generated by card i;
providing a set of at least two dCVV code corresponding to two successive dCVV time periods determined using the time base maintained by the server for the card and such that time TS falls within one of these time periods, a time period being defined as a duration and two time boundaries, the dCVV code associated to this period being called reference dCVV code;
if the dCVV code received from card i corresponds to one of the dCVV codes of the provided set but is different from the reference dCVV code, determine the minimum possible timing drift Min_td between the time base maintained by the server for the card and the time base Tbase(i) of the card, said minimum possible timing drift Min_td being deducted from the time difference between the closest time boundary of the period of time identified of the provided set corresponding to the dCVV received from the card and time TS;
updating time base Tbase(i) by addition of a time drift correction equal to the minimum possible time drift Min_td.
10. The server according to claim 9 , wherein the number of dCVV codes in the provided set corresponds to a tolerance window of a predefined number of successive dCVV codes to be included in said set.
11. The server according to claim 10 , wherein the tolerance window comprises three successive dCVV codes centred on the reference dCVV code.
12. The server according to claim 9 , wherein the number of dCVV codes in the provided set is derived from a tolerance window corresponding to a predefined time duration.
13. The server according to claim 9 , comprising a step for determining a deviation coefficient DC configured to adapt the update frequency/f card (i) of the time base Tbase(i) maintained by the server for card i, the deviation coefficient DC being derived from the minimum possible time drift Min_td.
14. The server according to claim 13 , wherein the deviation coefficient is determined using the following expression:
D
C
=
1
+
{
Min_td
T
S
-
T
0
}
where T0 represents the initial date or time clock setting of the card, the clock frequency/f card (i) applied to update time base Tbase(i) being updated using the following expression:
f card ( i )=DC× f TAI
where f TAI represents the clock frequency of the server which is taken as a reference.
15. The server according to claim 13 , wherein the deviation coefficient DC is determined using at least two successive time drift estimations Min_td performed by the server for this card and by applying a function on these at least two estimations to reduce bias of estimation.
16. The server according to claim 15 , wherein the function to reduce the bias of estimation is chosen among: an average function, a linearization function based on the method of least squares, a sin(x)/x interpolation.
17. A non-transitory machine-readable storage medium server having stored thereon a computer program for compensating by a server a clock deviation of a card i by maintaining a time base Tbase(i) synchronized with card i, comprising instructions to cause the server to perform the steps:
receiving at a time TS a dynamic card verification dCVV code value generated by card i;
providing a set of at least two dCVV code corresponding to two successive dCVV time periods determined using the time base maintained by the server for the card and such that time TS falls within one of these time periods, a time period being defined as a duration and two time boundaries, the dCVV code associated to this period being called reference dCVV code;
if the dCVV code received from card i corresponds to one of the dCVV codes of the provided set but is different from the reference dCVV code, determine the minimum possible timing drift Min_td between the time base maintained by the server for the card and the time base Tbase(i) of the card, said minimum possible timing drift Min_td being deducted from the time difference between the closest time boundary of the period of time identified of the provided set corresponding to the dCVV received from the card and time TS;
updating time base Tbase(i) by addition of a time drift correction equal to the minimum possible time drift Min_td.
18. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 17 , wherein the number of dCVV codes in the provided set corresponds to a tolerance window of a predefined number of successive dCVV codes to be included in said set.
19. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 18 , wherein the tolerance window comprises three successive dCVV codes centred on the reference dCVV code.
20. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 17 , wherein the number of dCVV codes in the provided set is derived from a tolerance window corresponding to a predefined time duration.
21. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 17 , comprising a step for determining a deviation coefficient DC configured to adapt the update frequency/f card (i) of the time base Tbase(i) maintained by the server for card i, the deviation coefficient DC being derived from the minimum possible time drift Min_td.
22. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 21 , wherein the deviation coefficient is determined using the following expression:
D
C
=
1
+
{
Min_td
T
S
-
T
0
}
where T0 represents the initial date or time clock setting of the card, the clock frequency/f card (i) applied to update time base Tbase(i) being updated using the following expression:
f card ( i )=DC× f TAI
where f TAI represents the clock frequency of the server which is taken as a reference.
23. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 21 , wherein the deviation coefficient DC is determined using at least two successive time drift estimations Min_td performed by the server for this card and by applying a function on these at least two estimations to reduce bias of estimation.
24. The non-transitory machine-readable storage medium server having stored thereon a computer program according to claim 23 , wherein the function to reduce the bias of estimation is chosen among: an average function, a linearization function based on the method of least squares, a sin(x)/x interpolation.