IDEA (International Data Encryption Algorithm) is the second version of a block cipher designed and presented by Lai and Massey. It is a 64-bit iterative block cipher with a 128-bit key and eight rounds. While the cipher is not Feistel, decryption is carried out in the same manner as encryption once the decryption subkeys have been calculated from the encryption subkeys. The cipher structure was designed to be easily implemented in both software and hardware, and the security of IDEA relies on the use of three incompatible types of arithmetic operations on 16-bit words. The speed of IDEA in software is similar to that of DES.
RC5 is a fast block cipher designed by Rivest for RSA Data Security. It is a parameterized algorithm with a variable block size, a variable key size, and a variable number of rounds. The block size can be 32, 64, or 128 bits long. The number of rounds can range from 0 to 255. The key can range from 0 bits to 2048 bits in size. Such built-in variability provides flexibility in levels of security and efficiency.
There are three routines in RC5: key expansion, encryption , and decryption. In the key-expansion routine, the user-provided secret key is expanded to fill a key table whose size depends on the number of rounds. The key table is then used in both encryption and decryption. The encryption routine consists of three primitive operations: addition, bitwise exclusive-or, and rotation. The exceptional simplicity of RC5 makes it easy to implement and analyze. Indeed, like RSA, RC5 can be written on the "back of the envelope" (except for key expansion).
RC2 is a variable key-size block cipher designed by Rivest for RSA Data Security. "RC" stands for "Ron's Code" or "Rivest's Cipher." It is faster than DES and is designed as a "drop-in" replacement for DES. It can be made more secure or less secure than DES against exhaustive key search by using appropriate key sizes. It has a block size of 64 bits and is about two to three times faster than DES in software. The algorithm is confidential and proprietary to RSA Data Security. RC2 can be used in the same modes as DES.
G-DES was devised by Schaumuller-Bichl to improve on the performance of DES by defining a cipher based on DES with a larger block size, but without an increase in the amount of computation required. It was claimed that G-DES was as secure as DES since the cipher was based on DES. However, Biham and Shamir showed that G-DES with the recommended parameter sizes is easily broken and that any alterations of G-DES parameters that result in a cipher faster than DES are less secure than DES.
Until recently, the most significant use of triple-DES was for the encryption of single DES keys, and there was really no need to consider how one might implement various block cipher modes when the block cipher in question is actually one derived from multiple encryption. However, as DES nears the end of its useful lifetime, more thought is being given to an increasingly widespread use of triple-DES.
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