CIPHER STRENGTH EVALUATION DEVICE, CIPHER STRENGTH EVALUATION METHOD, AND CIPHER STRENGTH EVALUATION PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide a cipher strength evaluation device, a cipher strength evaluation method and a cipher evaluation program, for reducing necessary calculation quantity in the case of evaluating the cipher strength of a common key block cipher by solving an attack equation.;SOLUTION: A cipher strength evaluation device 100 is provided with: a formula development part 103 for developing an attack equation generated by a formula generation part 101; and a formula arrangement part 105 for arranging development formulas by summarizing them by ciphertext terms from a primary term to a high order term existing in the developed attack equation. Furthermore, the cipher strength evaluation device 100 is provided with: an equivalent key replacement part 107 for replacing a polynomial including each order term of a secret key as the coefficients of each order term of a ciphertext with a primary equivalent key in the arranged attack equation; a number of unknown term detection part 109 for detecting the number of unknown terms relating to the equivalent key: and a cipher strength evaluation part 111 for estimating the number of selection plain text groups and calculation quantity necessary for calculating equivalent keys based on the number of unknown items.;COPYRIGHT: (C)2008,JPO&INPIT