Field-Programmable Gate Arrays: Reconfigurable Logic for Rapid Prototyping and Implementation of Digital Systems

6.3   DES ENCRYPTION

In 1977 the United States National Bureau of Standards (NBS) promulgated a new standard for encryption of unclassified data [NBS77] based on a proposal by IBM, the Design Encryption Standard (DES). Since then, this algorithm has become the de facto standard for data encryption worldwide. The algorithm is very suitable for implementation in hardware and several commercial products are available. In this section, we first outline the DES algorithm and secondly develop an implementation. DES provides an excellent example of an algorithm that can be speeded up greatly by bit-level hardware implementation. In this section, we develop a CAL implementation of DES: a more detailed presentation of this work appeared in [Kean89].

DES is a substitution cipher on 64-bit binary vectors based on a 56-bit key. The strength of DES lies in the complexity of the substitution. Two good introductions to DES are [Tanenb81], and for a more in-depth analysis [Konh85].

6.3.1   The DES Process

The DES algorithm is illustrated in Figure 6–4. All the f-boxes are identical, and it is obvious that a major design decision is whether to have one reusable f-box, or 16 separate ones to allow pipelining. We will consider the major components in the block diagram individually. We will try to give an idea of the size of the wiring channels (unfortunately channel density cannot be quoted because it depends on the ordering and spacing of the ports, which is implementation-dependent) and we will ...