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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 cryptanalysis seems to indicate that DES has a very strong internal structure.
Internet Security. Edited by M.Y. Rhee
© 2003 John Wiley & Sons, Ltd ISBN 0-470-85285-2