ELECTRONIC CASH METHOD USING PLURAL TRUST INSTITUTIONS

摘要

PROBLEM TO BE SOLVED: To cope with such a case where the keys of banks or trust institutions are stolen or extorted. SOLUTION: A user produces a random number λ corresponding to the electronic paper money C and also produces the random numbers λ1 ...λt-1 (210), obtains the open key ciphers E1 (λ(1))...Et (λ(t)) (230) where λ(t) equals λ+λ1 x+...+λt-1 x mod n to send these ciphers to the trust institutions T1 ...Tt , calculates g (N||λ) from λ, N and a unidirectional function (g), and then calculates Z=g (N||λ) R mod nw from a random number R and the open keys ew and nw (222, 223) to sends Z to a bank. The bank tentatively signs θ=Z mod nw by the secret keys dw and nw and sends θ to a user. The user calculates C=θ/R mod nw to obtain a genuine digital signature and uses C as cash. The institutions T1 ... Tt take out λ(1)...x(t) by the request of a court of justice, calculate λ(x)=λ+λ1 x+...+λt-1 x mod r, restore the number λ to send a table of all λ to a retail store or to answer the presence or absence of the number λ against the inquiry of the retail store.