| 摘要 |
PROBLEM TO BE SOLVED: To increase decoding speed in homomorphic encryption scheme with an extended plain text space.SOLUTION: An input of cipher text of an n-th dimensional vector having values of all 0 other than a first element or an input of the first element of value c is received (step S1). From an inverse matrix Vof an n-th regular matrix V as a secret key and the elements of matrix W=dVdefined by a specific formula which is Hermitian standard form of a matrix V used for encryption as a public key, an element w which is coprime with a plain text space size s is acquired (step S2). A computer further acquires an inverse wof w under a divisor s (step S3). Using a value [c×w]which is adjusted so that c×w mod d is included in a range [-d/2, d/2], the plain text b=[c×w]×wmod s is calculated (step S4), and output (step S5). |
