Abstract
Despite recent improvements in analytic techniques for attacking the
Data Encryption Standards (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 recetnly 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
prudent in many applications to use DES in a triple-encryption mode.
