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Abstract

A data encrypting system according to the CBC system involves a limitation in a range of a numerical value which expresses data (smaller than a predetermined integer N). The encrypting system has an encrypting apparatus including a block encrypting section for receiving data, which is expressed by an integer value X smaller than a predetermined integer value N, for executing a data conversion C=enc (X) where 0.ltoreq.C.ltoreq.N-1 using an RSA algorithm, and for outputting C; and an arithmetic operating section connected to receive data, as one input, which is expressed by an integer value M smaller than the integer value N, and the output C of the block encrypting section as the other input, for performing an arithmetic operation for both of the inputs so that a resultant arithmetic value is smaller than the integer value N, and for outputting the arithmetic value as an input of the block encrypting section. Further, a decoding apparatus has a block decoding section for receiving data which is expressed by an integer value C smaller than the integer value N, for executing an inverse conversion Y=dec (C) of the encrypting for the input signal by using the RSA algorithm; and a modulo subtracting section for subtracing the input data C from the output Y of the block decoding section and for outputting a remainder M' M'=Y-C (mod N) which is derived by dividing a resultant subtracted value by the integer value N.

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