ON-LINE OFF-LINE DIGITAL-SIGNATURES

A new type of signature scheme is proposed. It consists of two phases. The first phase is performed off-line, before the message to be signe d is even known. The second phase is performed on-line, once the messa ge to be signed is known, and is supposed to be very fast. A method fo r constructing such on-line/off-line signature schemes is presented. T he method uses one-time signature schemes, which are very fast, for th e on-line signing. An ordinary signature scheme is used for the off-li ne stage. In a practical implementation of our scheme, we use a varian t of Rabin's signature scheme (based on factoring) and DES. ln the on- line phase all we use is a moderate amount of DES computation and a si ngle modular multiplication. We stress that the costly modular exponen tiation operation is performed off-line. This implementation is ideall y suited for electronic wallets or smart cards.