France Telecom

Loic Juniot

Matthew Robshaw

Marc Girault

Henri Gilbert

A system and a method for cryptographic reduced-coupon reloading are provided, where a coupon includes a pseudo-random number r=PRF(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=&#x192;(r), where &#x192; is a predetermined one-way function, where: a candidate device and a second device acquire a common value of a token T, the candidate device transmits a verification value vto the second device, the second device verifies whether the verification value is equal to PRF'(T), where PRF&#x2032; is a predetermined keyed pseudo-random function identical to, or derived from, the pseudo-random function PRF, 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, one or several reduced-coupon(s) provided by the candidate device are stored in the second device.

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Loic Juniot