Fast DES implementations for FPGAs and its application to a universal key-search machine

Abstract

Most modern security protocols and security applications are defined to be algorithm independent, that is, they allow a choice from a et of cryptographic algorithms for the same function. Although an algorithm switch is rather difficult with traditional hardware, i.e., ASIC, implementations, Field Programmable Gate Arrays (FPGAs) offer a promising solution. Similarly, an ASIC-based key search machine is in general only applicable to one specific encryption algorithm. However, a key-search machine based on FPGAs can also be algorithm independent and thus be applicable to a wide variety of ciphers. We researched the feasibility of a universal key-search machine using the Data Encryption Standard (DES) as an example algorithm. We designed, implemented and compared various architecture options of DES with strong emphasis on high-speed performance. Techniques like pipelining and loop unrolling were used and their effectiveness for DES on FPGAs investigated. The most interesting result is that we could achieve encryption rates beyond 400 Mbit/s using a standard Xilinx FPGA. This result is by a factor of about 30 faster than software implementations while we are still maintaining flexibility. A DES cracker chip based on this design could search 6.29 million keys per second.