Vaccine: A Block Cipher Method for Masking and Unmasking of Ciphertexts' Features

摘要

A ciphertext inherits some properties of the plaintext, which is considered as a source of vulnerability and, therefore, it may be decrypted through a vigorous datamining process. Masking the ciphertext is the solution to the problem. In this paper, we have developed a new block cipher technique named Vaccine for which the block size is random and each block is further divided into segments of random size. Each byte within a segment is instantiated using a dynamic multi-instantiation approach, which means (i) the use of Vaccine does not produce the same masked outcome for the same given ciphertext and key and (ii) the options for masking different occurrences of a byte is extremely high. Two sets (100 members in each) of 1K long plaintexts of natural (borrowed from natural texts) and synthesized (randomly generated from 10 characters to increase the frequency of characters in the plaintext) are built. For each plaintext, two ciphertexts are generated using Advanced Encryption System (AES-128) and Data Encryption Standard (DES) algorithms. Vaccine and two well-known masking approaches of Cipher Block Chaining (CBC), and Cipher Feedback (CFB) are applied separately on each ciphertext. On average: (a) the Hamming distance between masked and unmasked occurrences of a byte using Vaccine is 0.72 bits higher than using the CBC, and CFB, and (b) Vaccine throughput is also 3.4 times and 1.8 times higher than the throughput for CBC and CFB, correspondingly, and (c) Vaccine masking strength is 1.5% and 1.8% higher than the masking strength for CBC and CFB, respectively.