Patent ID: 8543812

Claim:
A method for cryptographic reduced-coupon reloading, wherein a coupon comprises a pseudo-random number r i =PRF K (i), where i is an index for labeling the coupon, PRF is a predetermined pseudo-random function and K is a regeneration key, and a “reduced-coupon” x i such that x i =ƒ(r i ), where ƒ is a predetermined one-way function, said method comprising the following steps: verifying that a number of reduced-coupons x i that are pre-stored in a second device has reached a predetermined low amount, acquiring, by a candidate device and the second device, a common value of a token T, transmitting from said candidate device a verification value v T to the second device, verifying, by the second device whether said verification value v T is given by v T =PRF′ Q (T), where PRF′ is a predetermined keyed pseudo-random function identical to, or derived from, said pseudo-random function PRF, and where Q is an authentication key owned by the second device and known to the candidate device provided the candidate device is a legitimate reloading device, and if the verification is positive, storing one or several reduced-coupon(s) provided by the candidate device in the second device.