Strength of two data encryption standard implementations under timing attacks

Abstract

We study the vulnerability of two implementations of the Data Encryption Standard (DES) cryptosystem under a timing attack. A timing attack is a method, recently proposed by Paul Kocher, that is designed to break cryptographic systems. It exploits the engineering aspects involved in the implementation of cryptosystems and might succeed even against cryptosys-tems that remain impervious to sophisticated cryptanalytic techniques. A timing attack is, essentially, a way of obtaining some users private information by carefully measuring the time it takes the user to carry out cryptographic operations. In this work, we analyze two implementations of DES. We show that a timing attack yields the Hamming weight of the key used by both DES implementations. Moreover, the attack is computationally inexpensive. We also show that all the design characteristics of the target system, necessary to carry out the timing attack, can be inferred from timing measurements.