Identification of Encryption Method for Block Ciphers using Histogram Method

Abstract

In this paper, we propose a histogram based method for identification of encryption method from a cipher text obtained using a block cipher. Frequency of occurrence of symbols formed by groups of bits in the cipher text, is obtained to build a histogram. The proposed method is seen to be efficient for ECB mode. We also show that the entropy based on the probabilities of symbols in the cipher texts can be used to distinguish between the ECB and CBC modes. Finally, we propose a multiple histogram based method for identifying the starting position of a block in a cipher text for the ECB mode of encryption.