DES

Abstract

In 1974 the National Bureau of Standards (NBS) solicited the American industry to develop a cryptosystem that could be used as a standard in unclassified U.S. Government applications. IBM developed a system called LUCIFER. After being modified and simplified, this system became the Data Encryption Standard (DES) in 1977. It has been implemented on a chip, which makes it very suitable for use in large communication systems. The encryption and decryption algorithms of DES have been made public. This has never been done before, although in each textbook one can find the remark that the security of a cryptosystem should not depend on the secrecy of the system. Later we shall give a complete description of DES. DES is a block cipher operating on 64 bits simultaneously (see Figure 6.1). Although the keysize is 64, the effective keysize is 56 bits. The remaining 8 bits are parity checks. The input M and key K result in a ciphertext C, which we shall denote by DES(M,K). For the decryption the same DES chip with the same key can be used, as we shall see later.