PUBLIC KEY CIPHERING METHOD AND PUBLIC KEY CIPHERING COMMUNICATION SYSTEM

摘要

PROBLEM TO BE SOLVED: To make difficulty of decoding equivalent to difficulty of factorization into prime factors, to attain definite decoding with additional information of a simple calculation and to attain high speed decoding. ;SOLUTION: A key generator 310 generates two primes p, q, to obtain n=pq, and a value (n) is registered in a public file device 110 as a ciphering key and the values p, q are stored in a decoder 320 as decoding keys. A ciphering device 210 uses the ciphering key (n) and a plain text M, a point C=(c_x, c_y) obtained doubling the plain text N=(m_x, m_y) on an ellipse by²=x³+x(mad n) is used for a ciphered text and additional information (e) and the ciphered text are sent. A decoder 320 uses decoding keys p, q to apply a multiple of 1/2 to the ciphered text C on the ellipse by²=x³+x(mod p, q) to obtain objects M₁(i=1-4). In this case, a formula of a solution of a quartic equation is used. The plain text M is selected by using the additional information (e) from the objects M₁.;COPYRIGHT: (C)1997,JPO