In Chapter 3, we have defined cryptosystems and we have described some historical examples. All of the cryptosystems in Chapter 3 could all be broken because they are affine linear. A cryptosystem with perfect secrecy, the Vernam one-time pad, was presented in Chapter 4, but it turns out to be very inefficient. In this chapter, we describe the Data Encryption Standard (DES). For many years, this cryptosystem was the encryption standard in the U.S. and was used worldwide. Today, simple DES is no longer secure and the US National Institute of Standards (NIST) has chosen the Rijndael cryptosystem as the Advanced Encryption Standard (AES)  (see Chapter 6). AES is described in Chapter 6. Nevertheless, there are secure variants of DES (see Section 3.7) that are widely use. Also, DES remains an important model for the construction of secure block ciphers.
KeywordsBlock Cipher Block Length Advance Encryption Standard Secure Variant Data Encryption Standard
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