Metamorphic testing for block ciphers

Information is indispensable in modern society. People’s daily communication and work depend on information transmission. Unsafe storage or transmission of data may result in privacy and security problems. One way to attempt to prevent such issues is to use encryption algorithms to transform information into encrypted forms. Because the encryption steps of most encryption algorithms are complex, deciding the correctness of the encrypted output may take a long time in practice. This kind of problem is called the Test Oracle problem. In contrast to traditional software testing, Metamorphic Testing (MT) does not focus on the correctness of each individual output, but examines whether the inputs and outputs of multiple executions of a Program Under Test (PUT) satisfy necessary relations of the PUT, called metamorphic relations. This paper reports on an experience of applying MT to test three encryption algorithms — Data Encryption Standard (DES), Triple Data Encryption Standard (3DES), and Advanced Encryption Standard (AES).