TR-244: Efficient DES Key Search

Abstract

Despite recent improvements in analytic techniques for attacking the Data Encryption Standard (DES), exhaustive key search remains the most practical and efficient attack. Key search is becoming alarmingly practical. We show how to build an exhaustive DES key search machine for $1 million that can find a key in 3.5 hours on average. The design for such a machine is described in detail for the purpose of assessing the resistance of DES to an exhaustive attack. This design is based on mature technology to avoid making guesses about future capabilities. With this approach. DES keys can be found one to two orders of magnitude faster than other recently proposed designs. The basic machine design can be adapted to attack the standard DES modes of operation for a small penalty in running time. The issues of development cost and machine reliability are examined as well. In light of this work, it would be pru(lent in many applications to use DES in a triple-encryption mode.