| 摘要 |
PROBLEM TO BE SOLVED: To keep safety against a passive attack or a selective enciphered sentence attack. SOLUTION: Assuming that (p) and (q) are prime numbers with respectively (k) bits, it is set n=p<2> 8, and h(m) composed on an irreducible remainder group (Z/nZ)* with (n) as a modulus is obtained by inputting a plain sentence (m) to unidirectional function equipment 114. This is bit linked with (m) (115), M=m||h(m) is made to have k0 bits (0<k0 <k), a product nr (112) of a random number (r) and (n) is added with M and C=gM<+n> mod n is outputted as an enciphered sentence. The (g) is selected from (Z/nZ)* in which the rank of g<1> = g<t-1> mod p<2> in (Z/p<2> Z)* is equal to (p). With respect to C, C mod p<2> is found, further, Cp=C<p-1> mod p<2> is found, L(Cp)×L(gp )<-1> mod p=M is found and its high-order k<0> bits are defined as a deciphered plain sentence.
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