Process for generating DSA signatures with low-cost portable apparatuses

Process for generating digital signatures with a portable apparatus of the microprocessor-based integrated-circuit card type, the portable apparatus including a microprocessor, a communication device, and an electrically programmable non-volatile memory, the method comprising the steps of

• preparing a plurality of original coupons, the plurality of original coupons being prepared externally to the portable apparatus, the plurality of original coupons being formed of precomputed data useful in the generation of the digital signatures, wherein different coupons correspond to different individual signatures such that the generation of an individual signature involves the use of only a single coupon, and wherein the plurality of original coupons each correspond to an intermediate step in the calculation of the different individual signatures;
• loading the plurality of original coupons into the portable apparatus after the plurality of original coupons have been prepared;
• using the plurality of original coupons to generate the digital signatures;
• and
• periodically reloading the apparatus with pluralities of additional coupons after the apparatus has been issued to an end user and after the plurality of original coupons has been substantially exhausted, each performance of the reloading step comprising the steps of
• establishing a connection between a signature verification device and the apparatus, the signature verification device being formed of one of a verifier and a certified central authority,
• preparing a plurality of additional coupons,
• enciphering the plurality of additional coupons, and
• sending the plurality of additional coupons from the signature verification device to the apparatus in enciphered format, the plurality of additional coupons enabling the apparatus to generate a plurality of additional digital signatures.