On a method of cryptanalysis for cryptosystem with involution

Abstract

AbstractCryptology provides the technological basis for guaranteed network security. In the field of business, to guarantee the security of information, everyone needs easy‐to‐use cryptology. Starting with the announcement by the U.S. National Bureau of Standards of the DES cryptosystem and the proposal by NTT of the FEAL cryptosystem, secret‐key cryptographic algorithms have been published, involution‐type block cryptosystems which use secret key to encipher 64 bits of plain text as 64 bits of cipher text [2, 3, 9, 10, 12]. NTT has pro posed the one‐way function MAP, which is also an invo lution‐type transform. In this paper, we study a new cryptanalytic method for involution‐type cryptosystems and show by example that it can be applied practically in a ciphertext‐only attack on the one‐way function MAP. For an involution‐type cryptosystem, by increasing the amount of construction in the data‐randomization phase and by increasing the size of the secret key, we can guarantee the computational security by preventing the estimation of the secret key. However, if we study the properties of the function used in the design of the data‐ randomization phase, by specifying input/output values of the function which are independent of the secret key, it may be possible to use the inverse function [11] to calculate the secret key. This method is called the inter Mediate cipher method. the intermediate cipher method differs from previous methods in the small quantity of data required for breaking.