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Re: IDEA encryption
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 ([email protected]) */
/* 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.