International Data Encryption Algorithm

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International Data Encryption Algorithm

Fall 2004


How-Shen Chang

Table of Contents:

Description of IDEA3
Key Generation3
Modes of operation6
Weak keys for IDEA6


The Data Encryption Standard (DES) algorithm has been a popular secret key encryption algorithm and is used in many commercial and financial applications. Although introduced in 1976, it has proved resistant to all forms of cryptanalysis. However, its key size is too small by current standards and its entire 56 bit key space can be searched in approximately 22 hours [1]. International Data Encryption Algorithm (IDEA) is a block cipher designed by Xuejia Lai and James L. Massey of ETH-Zürich and was first described in 1991. It is a minor revision of an earlier cipher, PES (Proposed Encryption Standard); IDEA was originally called IPES (Improved PES). IDEA was used as the symmetric cipher in early versions of the Pretty Good Privacy cryptosystem. IDEA was to develop a strong encryption algorithm, which would replace the DES procedure developed in the U.S.A. in the seventies. It is also interesting in that it entirely avoids the use of any lookup tables or S-boxes. When the famous PGP email and file encryption product was designed by Phil Zimmermann, the developers were looking for maximum security. IDEA was their first choice for data encryption based on its proven design and its great reputation.

The IDEA encryption algorithm
• provides high level security not based on keeping the algorithm a secret, but rather upon ignorance of the secret key • is fully specified and easily understood
• is available to everybody
• is suitable for use in a wide range of applications
• can be economically implemented in electronic components (VLSI Chip) • can be used efficiently
• may be exported world wide
• is patent protected...
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