/* idea.c - C source code for IDEA block cipher.
* IDEA (International Data Encryption Algorithm), formerly known as
* IPES (Improved Proposed Encryption Standard).
* Algorithm developed by Xuejia Lai and James L. Massey, of ETH Zurich.
* This implementation modified and derived from original C code
* developed by Xuejia Lai.
* Zero-based indexing added, names changed from IPES to IDEA.
* CFB functions added. Random number routines added.
*
* Optimized for speed 21 Oct 92 by Colin Plumb.
* Very minor speedup on 23 Feb 93 by Colin Plumb.
* idearand() given a separate expanded key on 25 Feb 93, Colin Plumb.
*
* There are two adjustments that can be made to this code to
* speed it up. Defaults may be used for PCs. Only the -DIDEA32
* pays off significantly if selectively set or not set.
* Experiment to see what works better for you.
*
* Multiplication: default is inline, -DAVOID_JUMPS uses a
* different version that does not do any conditional
* jumps (a few percent worse on a SPARC), while
* -DSMALL_CACHE takes it out of line to stay
* within a small on-chip code cache.
* Variables: normally, 16-bit variables are used, but some
* machines (notably RISCs) do not have 16-bit registers,
* so they do a great deal of masking. -DIDEA32 uses "int"
* register variables and masks explicitly only where
* necessary. On a SPARC, for example, this boosts
* performace by 30%.
*
* The IDEA(tm) block cipher is covered by a patent held by ETH and a
* Swiss company called Ascom-Tech AG. The Swiss patent number is
* PCT/CH91/00117. International patents are pending. IDEA(tm) is a
* trademark of Ascom-Tech AG. There is no license fee required for
* noncommercial use. Commercial users may obtain licensing details
* from Dieter Profos, Ascom Tech AG, Solothurn Lab, Postfach 151, 4502
* Solothurn, Switzerland, Tel +41 65 242885, Fax +41 65 235761.
*
* The IDEA block cipher uses a 64-bit block size, and a 128-bit key
* size. It breaks the 64-bit cipher block into four 16-bit words
* because all of the primitive inner operations are done with 16-bit
* arithmetic. It likewise breaks the 128-bit cipher key into eight
* 16-bit words.
*
* For further information on the IDEA cipher, see these papers:
* 1) Xuejia Lai, "Detailed Description and a Software Implementation of
* the IPES Cipher", Institute for Signal and Information
* Processing, ETH-Zentrum, Zurich, Switzerland, 1991
* 2) Xuejia Lai, James L. Massey, Sean Murphy, "Markov Ciphers and
* Differential Cryptanalysis", Advances in Cryptology- EUROCRYPT'91
*
* This code assumes that each pair of 8-bit bytes comprising a 16-bit
* word in the key and in the cipher block are externally represented
* with the Most Significant Byte (MSB) first, regardless of the
* internal native byte order of the target CPU.
*/
#include "idea.h"
#ifdef TEST
#include <stdio.h>
#include <time.h>
#endif
#define ROUNDS 8 /* Don't change this value, should be 8 */
#define KEYLEN (6*ROUNDS+4) /* length of key schedule */
typedef word16 IDEAkey[KEYLEN];
#ifdef IDEA32 /* Use >16-bit temporaries */
#define low16(x) ((x) & 0xFFFF)
typedef unsigned int uint16; /* at LEAST 16 bits, maybe more */
#else
#define low16(x) (x) /* this is only ever applied to uint16's */
typedef word16 uint16;
#endif
#ifdef _GNUC_
/* __const__ simply means there are no side effects for this function,
* which is useful info for the gcc optimizer */
#define CONST __const__
#else
#define CONST
#endif
static void en_key_idea(word16 *userkey, word16 *Z);
static void de_key_idea(IDEAkey Z, IDEAkey DK);
static void cipher_idea(word16 in[4], word16 out[4], CONST IDEAkey Z);
/*
* Multiplication, modulo (2**16)+1
* Note that this code is structured like this on the assumption that
* untaken branches are cheaper than taken branches, and the compiler
* doesn't schedule branches.
*/
#ifdef SMALL_CACHE
CONST static uint16 mul(register uint16 a, register uint16 b)
{
register word32 p;
if (a)
{ if (b)
{ p = (word32)a * b;
b = low16(p);
a = p>>16;
return b - a + (b < a);
}
else
{ return 1-a;
}
}
else
{ return 1-b;
}
} /* mul */
#endif /* SMALL_CACHE */
/*
* Compute multiplicative inverse of x, modulo (2**16)+1,
* using Euclid's GCD algorithm. It is unrolled twice to
* avoid swapping the meaning of the registers each iteration,
* and some subtracts of t have been changed to adds.
*/
CONST static uint16 inv(uint16 x)
{
uint16 t0, t1;
uint16 q, y;
if (x <= 1)
return x; /* 0 and 1 are self-inverse */
t1 = 0x10001L / x; /* Since x >= 2, this fits into 16 bits */
y = 0x10001L % x;
if (y == 1)
return low16(1-t1);
t0 = 1;
do
{ q = x / y;
x = x % y;
t0 += q * t1;
if (x == 1)
return t0;
q = y / x;
y = y % x;
t1 += q * t0;
} while (y != 1);
return low16(1-t1);
} /* inv */
/* Compute IDEA encryption subkeys Z */
static void en_key_idea(word16 *userkey, word16 *Z)
{
int i,j;
/*
* shifts
*/
for (j=0; j<8; j++)
Z[j] = *userkey++;
for (i=0; j<KEYLEN; j++)
{ i++;
Z[i+7] = Z[i & 7] << 9 | Z[i+1 & 7] >> 7;
Z += i & 8;
i &= 7;
}
} /* en_key_idea */
/* Compute IDEA decryption subkeys DK from encryption subkeys Z */
/* Note: these buffers *may* overlap! */
static void de_key_idea(IDEAkey Z, IDEAkey DK)
{
int j;
uint16 t1, t2, t3;
IDEAkey T;
word16 *p = T + KEYLEN;
t1 = inv(*Z++);
t2 = -*Z++;
t3 = -*Z++;
*--p = inv(*Z++);
*--p = t3;
*--p = t2;
*--p = t1;
for (j = 1; j < ROUNDS; j++)
{
t1 = *Z++;
*--p = *Z++;
*--p = t1;
t1 = inv(*Z++);
t2 = -*Z++;
t3 = -*Z++;
*--p = inv(*Z++);
*--p = t2;
*--p = t3;
*--p = t1;
}
t1 = *Z++;
*--p = *Z++;
*--p = t1;
t1 = inv(*Z++);
t2 = -*Z++;
t3 = -*Z++;
*--p = inv(*Z++);
*--p = t3;
*--p = t2;
*--p = t1;
/* Copy and destroy temp copy */
for (j = 0, p = T; j < KEYLEN; j++)
{
*DK++ = *p;
*p++ = 0;
}
} /* de_key_idea */
/*
* MUL(x,y) computes x = x*y, modulo 0x10001. Requires two temps,
* t16 and t32. x must me a side-effect-free lvalue. y may be
* anything, but unlike x, must be strictly 16 bits even if low16()
* is #defined.
* All of these are equivalent - see which is faster on your machine
*/
#ifdef SMALL_CACHE
#define MUL(x,y) (x = mul(low16(x),y))
#else
#ifdef AVOID_JUMPS
#define MUL(x,y) (x = low16(x-1), t16 = low16((y)-1), \
t32 = (word32)x*t16+x+t16+1, x = low16(t32), \
t16 = t32>>16, x = x-t16+(x<t16) )
#else
#define MUL(x,y) ((t16 = (y)) ? (x=low16(x)) ? \
t32 = (word32)x*t16, x = low16(t32), t16 = t32>>16, \
x = x-t16+(x<t16) : \
(x = 1-t16) : (x = 1-x))
#endif
#endif
/* IDEA encryption/decryption algorithm */
/* Note that in and out can be the same buffer */
static void cipher_idea(word16 in[4], word16 out[4], register CONST IDEAkey Z)
{
register uint16 x1, x2, x3, x4, s2, s3;
#ifndef SMALL_CACHE
register uint16 t16;
register word32 t32;
#endif
int r = ROUNDS;
x1 = *in++; x2 = *in++;
x3 = *in++; x4 = *in;
do
{
MUL(x1,*Z++);
x2 += *Z++;
x3 += *Z++;
MUL(x4, *Z++);
s3 = x3;
x3 ^= x1;
MUL(x3, *Z++);
s2 = x2;
x2 ^= x4;
x2 += x3;
MUL(x2, *Z++);
x3 += x2;
x1 ^= x2;
x4 ^= x3;
x2 ^= s3;
x3 ^= s2;
} while (--r);
MUL(x1, *Z++);
*out++ = x1;
*out++ = x3 + *Z++;
*out++ = x2 + *Z++;
MUL(x4, *Z);
*out = x4;
} /* cipher_idea */
/*-------------------------------------------------------------*/
#ifdef TEST
/*
* This is the number of Kbytes of test data to encrypt.
* It defaults to 1 MByte.
*/
#ifndef KBYTES
#define KBYTES 1024
#endif
void main(void)
{ /* Test driver for IDEA cipher */
int i, j, k;
IDEAkey Z, DK;
word16 XX[4], TT[4], YY[4];
word16 userkey[8];
clock_t start, end;
long l;
/* Make a sample user key for testing... */
for(i=0; i<8; i++)
userkey[i] = i+1;
/* Compute encryption subkeys from user key... */
en_key_idea(userkey,Z);
printf("\nEncryption key subblocks: ");
for(j=0; j<ROUNDS+1; j++)
{
printf
