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Symmetric Block Ciphers Chương này sẽ đề cập với một số thuật toán mật mã khối quan trọng đã được phát triển trong quá khứ. Họ là IDEA (1992), RC5 (1995), rc6 (1996), DES (1977) và AES (2001). Advanced Encryption Standard (AES) xác định một thuật toán mã hóa FIPS-phê duyệt khối đối xứng sẽ sớm đến để được sử dụng thay cho Triple DES hoặc rc6. | 3 Symmetric Block Ciphers This chapter deals with some important block ciphers that have been developed in the past. They are IDEA 1992 RC5 1995 RC6 1996 DES 1977 and AES 2001 . The Advanced Encryption Standard AES specifies a FIPS-approved symmetric block cipher which will soon come to be used in lieu of Triple DES or RC6. 3.1 Data Encryption Standard DES In the late 1960s IBM initiated a Lucifer research project led by Horst Feistel for computer cryptography. This project ended in 1971 and LUCIFER was first known as a block cipher that operated on blocks of 64 bits using a key size of 128 bits. Soon after this IBM embarked on another effort to develop a commercial encryption scheme which was later called DES. This research effort was led by Walter Tuchman. The outcome of this effort was a refined version of Lucifer that was more resistant to cryptanalysis. In 1973 the National Bureau of Standards NBS now the National Institute of Standards and Technology NIST issued a public request for proposals for a national cipher standard. IBM submitted the research results of the DES project as a possible candidate. The NBS requested the National Security Agency NSA to evaluate the algorithm s security and to determine its suitability as a federal standard. In November 1976 the Data Encryption Standard was adopted as a federal standard and authorised for use on all unclassified US government communications. The official description of the standard FIPS PUB 46 Data Encryption Standard was published on 15 January 1977. The DES algorithm was the best one proposed and was adopted in 1977 as the Data Encryption Standard even though there was much criticism of its key length which had changed from Lucifer s original 128 bits to 64 bits and the design criteria for the internal structure of DES i.e. S-box. Nevertheless DES has survived remarkably well over 20 years of intense cryptanalysis and has been a worldwide standard for over 18 years. The recent work on differential .
