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idea.c
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C/C++ Source or Header
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2000-05-18
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/* 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 <colin@nsq.gts.org>. 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 internal native byte order of the target CPU. */
#include "idea.h"
#define min(x, y) (((x) < (y)) ? (x) : (y))
#ifdef TEST
#include <stdio.h>
#include <time.h>
#endif
#ifdef sgi
#define HIGHFIRST
#endif
#ifdef sun
#define HIGHFIRST
#define const
#endif
#define TRUE 1
#define FALSE 0
#define IDEABLOCKSIZE 8
#define ROUNDS 8 /* Don't change this value, should be 8 */
#define KEYLEN (6*ROUNDS+4) /* length of key schedule */
#define byte unsigned char
#define word16 unsigned short
#define boolean int
#define word32 unsigned long
#define byteptr unsigned char *
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();
static void de_key_idea();
static void cipher_idea();
/* 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;
}
}
#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; some subtracts of t have been changed to adds. */
CONST static uint16 inv(x)
uint16 x;
{
uint16 t0, t1;
uint16 q, y;
if (x <= 1)
return x; /* 0 and 1 are self-inverse */
t1 = 0x10001 / x; /* Since x >= 2, this fits into 16 bits */
y = 0x10001 % 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);
}
/* Compute IDEA encryption subkeys Z */
static void en_key_idea(userkey, Z)
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;
}
}
/* Compute IDEA decryption subkeys DK from encryption subkeys Z */
/* Note: these buffers *may* overlap! */
static void de_key_idea(Z, DK)
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;
}
}
/* 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 . In/out can be the same buffer */
static void cipher_idea(in, out, Z)
word16 in[4]; word16 out[4]; register CONST IDEAkey Z;
{
register uint16 x1, x2, x3, x4, t1, t2;
register uint16 t16;
register word32 t32;
int r = ROUNDS;
x1 = *in++; x2 = *in++;
x3 = *in++; x4 = *in;
do
{
MUL(x1,*Z++);
x2 += *Z++;
x3 += *Z++;
MUL(x4, *Z++);
t2 = x1^x3;
MUL(t2, *Z++);
t1 = t2 + (x2^x4);
MUL(t1, *Z++);
t2 = t1+t2;
x1 ^= t1;
x4 ^= t2;
t2 ^= x2;
x2 = x3^t1;
x3 = t2;
} while (--r);
MUL(x1, *Z++);
*out++ = x1;
*out++ = x3 + *Z++;
*out++ = x2 + *Z++;
MUL(x4, *Z);
*out = x4;
}
#ifdef TEST
/* Number of Kbytes of test data to encrypt. Defaults to 1 MByte. */
#ifndef KBYTES
#define KBYTES 1024
#endif
#ifndef CLOCKS_PER_SEC
#define CLOCKS_PER_SEC 1000000
#endif
int main()
{ /* 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("\nround %d: ", j+1);
if (j==ROUNDS)
for(i=0; i<4; i++)
printf(" %6u", Z[j*6+i]);
else
for(i=0; i<6; i++)
printf(" %6u", Z[j*6+i]);
}
/* Compute decryption subkeys from encryption subkeys... */
de_key_idea(Z,DK);
printf("\nDecryption key subblocks: ");
for(j=0; j<ROUNDS+1; j++)
{
printf("\nround %d: ", j+1);
if (j==ROUNDS)
for(i=0; i<4; i++)
printf(" %6u", DK[j*6+i]);
else
for(i=0; i<6; i++)
printf(" %6u", DK[j*6+i]);
}
/* Make a sample plaintext pattern for testing... */
for (k=0; k<4; k++)
XX[k] = k;
printf("\n Encrypting %d KBytes (%ld blocks)...", KBYTES, KBYTES*64l);
fflush(stdout);
start = clock();
cipher_idea(XX,YY,Z); /* encrypt plaintext XX, making YY */
for (l = 1; l < 64*KBYTES; l++)
cipher_idea(YY,YY,Z); /* repeated encryption */
cipher_idea(YY,TT,DK); /* decrypt ciphertext YY, making TT */
for (l = 1; l < 64*KBYTES; l++)
cipher_idea(TT,TT,DK); /* repeated decryption */
end = clock() - start;
l = end * 1000. / CLOCKS_PER_SEC + 1;
i = l/1000;
j = l%1000;
l = KBYTES * 1024. * CLOCKS_PER_SEC / end;
printf("%d.%03d seconds = %ld bytes per second\n", i, j, l);
printf("\nX %6u %6u %6u %6u \n",
XX[0], XX[1], XX[2], XX[3]);
printf("Y %6u %6u %6u %6u \n",
YY[0], YY[1], YY[2], YY[3]);
printf("T %6u %6u %6u %6u \n",
TT[0], TT[1], TT[2], TT[3]);
/* Now decrypted TT should be same as original XX */
for (k=0; k<4; k++)
if (TT[k] != XX[k])
{
printf("\n\07Error! Noninvertable encryption.\n");
exit(-1); /* error exit */
}
printf("\nNormal exit.\n");
return 0;
}
#endif /* TEST */
/* xorbuf - change buffer via xor with random mask block. Used for Cipher
* Feedback (CFB) or Cipher Block Chaining (CBC) modes of encryption. Can be
* applied for any block encryption algorithm, with any block size, such as
* the DES or the IDEA cipher. */
static void xorbuf(buf, mask, count)
register byteptr buf; register byteptr mask; register int count;
/* count must be > 0 */
{
if (count)
do
*buf++ ^= *mask++;
while (--count);
} /* xorbuf */
/* cfbshift - shift bytes into IV for CFB input. Used only for Cipher Feedback
* (CFB) mode of encryption. Can be applied for any block encryption algorithm
* with any block size, such as the DES or the IDEA cipher. */
static void cfbshift(iv, buf, count, blocksize)
register byteptr iv; register byteptr buf;
register int count; int blocksize;
/* iv is initialization vector. buf is buffer pointer. count is number of bytes
* to shift in...must be > 0. blocksize is 8 bytes for DES or IDEA ciphers. */
{
int retained;
if (count)
{
retained = blocksize-count; /* number bytes in iv to retain */
/* left-shift retained bytes of IV over by count bytes to make room */
while (retained--)
{
*iv = *(iv+count);
iv++;
}
/* now copy count bytes from buf to shifted tail of IV */
do *iv++ = *buf++;
while (--count);
}
} /* cfbshift */
/* Key schedules for IDEA encryption and decryption */
static IDEAkey Z, DK;
static word16 *iv_idea; /* pointer to IV for CFB or CBC */
static boolean cfb_dc_idea; /* TRUE iff CFB decrypting */
/* initkey_idea initializes IDEA for ECB mode operations */
void initkey_idea(key, decryp)
byte key[16]; boolean decryp;
{
word16 userkey[8]; /* IDEA key is 16 bytes long */
int i;
/* Assume each pair of bytes comprising a word is ordered MSB-first. */
for (i=0; i<8; i++)
{
userkey[i] = (key[0]<<8) + key[1];
key++; key++;
}
en_key_idea(userkey,Z);
if (decryp)
{
de_key_idea(Z,Z); /* compute inverse key schedule DK */
}
for (i=0; i<8; i++)/* Erase dangerous traces */
userkey[i] = 0;
} /* initkey_idea */
/* Run a 64-bit block thru IDEA in ECB (Electronic Code Book) mode, using the
* currently selected key schedule. */
void idea_ecb(inbuf, outbuf)
word16 *inbuf; word16 *outbuf;
{
/* Assume each pair of bytes comprising a word is ordered MSB-first. */
#ifndef HIGHFIRST /* If this is a least-significant-byte-first CPU */
word16 x;
/* Invert the byte order for each 16-bit word for internal use. */
x = inbuf[0]; outbuf[0] = x >> 8 | x << 8;
x = inbuf[1]; outbuf[1] = x >> 8 | x << 8;
x = inbuf[2]; outbuf[2] = x >> 8 | x << 8;
x = inbuf[3]; outbuf[3] = x >> 8 | x << 8;
cipher_idea(outbuf, outbuf, Z);
x = outbuf[0]; outbuf[0] = x >> 8 | x << 8;
x = outbuf[1]; outbuf[1] = x >> 8 | x << 8;
x = outbuf[2]; outbuf[2] = x >> 8 | x << 8;
x = outbuf[3]; outbuf[3] = x >> 8 | x << 8;
#else /* HIGHFIRST */
/* Byte order for internal and external representations is the same. */
cipher_idea(inbuf, outbuf, Z);
#endif /* HIGHFIRST */
} /* idea_ecb */
/* initcfb - Initializes IDEA key schedule tables via key; initializes Cipher
* Feedback mode IV. References context variables cfb_dc_idea and iv_idea. */
void initcfb_idea(iv0, key, decryp)
word16 iv0[4]; byte key[16]; boolean decryp;
/* iv0 is copied to global iv_idea, buffer will be destroyed by ideacfb. key is
* pointer to key buffer. decryp is TRUE if decrypting, FALSE if encrypting. */
{
iv_idea = iv0;
cfb_dc_idea = decryp;
initkey_idea(key,FALSE);
}
/* ideacfb - encipher a buffer with IDEA enciphering algorithm, using Cipher
* Feedback (CFB) mode. Assumes initcfb_idea has already been called.
* References context variables cfb_dc_idea and iv_idea. */
void ideacfb(buf, count)
byteptr buf; int count;
/* buf is input, output buffer, may be more than 1 block. count is byte count
* is byte count of buffer. May be > IDEABLOCKSIZE. */
{
int chunksize; /* smaller of count, IDEABLOCKSIZE */
word16 temp[IDEABLOCKSIZE/2];
while ((chunksize = min(count,IDEABLOCKSIZE)) > 0)
{
idea_ecb(iv_idea,temp); /* encrypt iv_idea, making temp. */
if (cfb_dc_idea)/* buf is ciphertext */
/* shift in ciphertext to IV... */
cfbshift((byte *)iv_idea,buf,chunksize,IDEABLOCKSIZE);
/* convert buf via xor */
xorbuf(buf,(byte *)temp,chunksize);/* buf has enciphered output */
if (!cfb_dc_idea)/* buf was plaintext, is now ciphertext */
/* shift in ciphertext to IV... */
cfbshift((byte *)iv_idea,buf,chunksize,IDEABLOCKSIZE);
count -= chunksize;
buf += chunksize;
}
}
/* close_idea function erases all the key schedule information when we are
* done with a set of operations for a particular IDEA key context. This is to
* prevent any sensitive data from being left around in memory. */
void close_idea() /* erase current key schedule tables */
{
short i;
for (i = 0; i < KEYLEN; i++)
Z[i] = 0;
} /* close_idea() */
/* These buffers are used by init_idearand, idearand, and close_idearand. */
static word16 dtbuf_idea[4] = {0}; /* buffer for enciphered timestamp */
static word16 randseed_idea[4] = {0}; /* seed for IDEA random # generator */
static word16 randbuf_idea[4] = {0}; /* buffer for IDEA random # generator */
static byte randbuf_idea_counter = 0; /* random bytes left in randbuf_idea */
/* init_idearand - initialize idearand, IDEA random number generator. Used for
* generating cryptographically strong random numbers. Much of design comes
* from Appendix C of ANSI X9.17. key is pointer to IDEA key buffer. seed is
* pointer to random number seed buffer. tstamp is a 32-bit timestamp */
void init_idearand(key, seed, tstamp)
byte key[16]; byte seed[8]; word32 tstamp;
{
int i;
initkey_idea(key, FALSE); /* initialize IDEA */
for (i=0; i<4; i++) /* capture timestamp material */
{ dtbuf_idea[i] = tstamp; /* get bottom word */
tstamp = tstamp >> 16; /* drop bottom word */
/* tstamp has only 4 bytes-- last 4 bytes will always be 0 */
}
/* Start with enciphered timestamp: */
idea_ecb(dtbuf_idea,dtbuf_idea);
/* initialize seed material */
for (i=0; i<8; i++)
((byte *)randseed_idea)[i] = seed[i];
randbuf_idea_counter = 0; /* # of random bytes left in randbuf_idea */
}
/* idearand - IDEA pseudo-random number generator. Used for generating
* cryptographically strong random numbers. Much of design comes from Appendix
* C of ANSI X9.17. */
byte idearand()
{
int i;
if (randbuf_idea_counter==0) /* if random buffer is spent...*/
{ /* Combine enciphered timestamp with seed material: */
for (i=0; i<4; i++)
randseed_idea[i] ^= dtbuf_idea[i];
idea_ecb(randseed_idea,randbuf_idea); /* fill new block */
/* Compute new seed vector: */
for (i=0; i<4; i++)
randseed_idea[i] = randbuf_idea[i] ^ dtbuf_idea[i];
idea_ecb(randseed_idea,randseed_idea); /* fill new seed */
randbuf_idea_counter = 8; /* reset counter for full buffer */
}
/* Take a byte from randbuf_idea: */
return(((byte *)randbuf_idea)[--randbuf_idea_counter]);
}
void close_idearand()
{ /* Erase random IDEA buffers and wipe out IDEA key info */
int i;
for (i=0; i<4; i++)
{ randbuf_idea[i] = 0;
randseed_idea[i] = 0;
dtbuf_idea[i] = 0;
}
close_idea();/* erase current key schedule tables */
}