On Tue, 12 Dec 1995, Derek Atkins wrote:
The copy of the source for idea (unix) that I have specify's a user key length of 8 bytes, but allows this to be increased to something larger. Will increasing the user keylength improve the overall security?
Umm, I think you are confused. First, IDEA has a keysize of 16 bytes, not 8. Second, it cannot be easily changed. Sure, your code probably
/******************************************************************************/ /* */ /* I N T E R N A T I O N A L D A T A E N C R Y P T I O N A L G O R I T H M */ /* */ /******************************************************************************/ /* Author: Richard De Moliner (demoliner@isi.ee.ethz.ch) */ /* Signal and Information Processing Laboratory */ /* Swiss Federal Institute of Technology */ /* CH-8092 Zuerich, Switzerland */ /* Created: April 23, 1992 */ /* Changes: November 16, 1993 (support of ANSI-C and C++) */ /* System: SUN SPARCstation, SUN acc ANSI-C-Compiler, SUN-OS 4.1.3 */ /******************************************************************************/ /* Change this type definitions to the representations in your computer. */ [snipped irrelivant bits] /******************************************************************************/ /* It is possible to change this values. */ #define Idea_nofRound 8 /* number of rounds */ #define Idea_userKeyLen 8 /* user key length (8 or larger) */ /******************************************************************************/ /* Do not change the lines below. */ #define Idea_dataLen 4 /* plain-/ciphertext block length*/ #define Idea_keyLen (Idea_nofRound * 6 + 4) /* en-/decryption key length */ #define Idea_dataSize (Idea_dataLen * 2) /* 8 bytes = 64 bits */ #define Idea_userKeySize (Idea_userKeyLen * 2) /* 16 bytes = 128 bits */ [end cut out] So what im reading here is; A) it is possible to change the value of the userkeylength, and B) the actual key is (2 * userkeylen) or in the case of an 8byte key, 2 * 8bytes = 16 bytes = 128bits. Maybe im crazy.