ltm-0.41
This commit is contained in:
Love Hornquist Astrand
321
lib/hcrypto/libtommath/bn_mp_exptmod_fast.c
Normal file
321
lib/hcrypto/libtommath/bn_mp_exptmod_fast.c
Normal file
@@ -0,0 +1,321 @@
|
||||
#include <tommath.h>
|
||||
#ifdef BN_MP_EXPTMOD_FAST_C
|
||||
/* LibTomMath, multiple-precision integer library -- Tom St Denis
|
||||
*
|
||||
* LibTomMath is a library that provides multiple-precision
|
||||
* integer arithmetic as well as number theoretic functionality.
|
||||
*
|
||||
* The library was designed directly after the MPI library by
|
||||
* Michael Fromberger but has been written from scratch with
|
||||
* additional optimizations in place.
|
||||
*
|
||||
* The library is free for all purposes without any express
|
||||
* guarantee it works.
|
||||
*
|
||||
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
|
||||
*/
|
||||
|
||||
/* computes Y == G**X mod P, HAC pp.616, Algorithm 14.85
|
||||
*
|
||||
* Uses a left-to-right k-ary sliding window to compute the modular exponentiation.
|
||||
* The value of k changes based on the size of the exponent.
|
||||
*
|
||||
* Uses Montgomery or Diminished Radix reduction [whichever appropriate]
|
||||
*/
|
||||
|
||||
#ifdef MP_LOW_MEM
|
||||
#define TAB_SIZE 32
|
||||
#else
|
||||
#define TAB_SIZE 256
|
||||
#endif
|
||||
|
||||
int mp_exptmod_fast (mp_int * G, mp_int * X, mp_int * P, mp_int * Y, int redmode)
|
||||
{
|
||||
mp_int M[TAB_SIZE], res;
|
||||
mp_digit buf, mp;
|
||||
int err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
|
||||
|
||||
/* use a pointer to the reduction algorithm. This allows us to use
|
||||
* one of many reduction algorithms without modding the guts of
|
||||
* the code with if statements everywhere.
|
||||
*/
|
||||
int (*redux)(mp_int*,mp_int*,mp_digit);
|
||||
|
||||
/* find window size */
|
||||
x = mp_count_bits (X);
|
||||
if (x <= 7) {
|
||||
winsize = 2;
|
||||
} else if (x <= 36) {
|
||||
winsize = 3;
|
||||
} else if (x <= 140) {
|
||||
winsize = 4;
|
||||
} else if (x <= 450) {
|
||||
winsize = 5;
|
||||
} else if (x <= 1303) {
|
||||
winsize = 6;
|
||||
} else if (x <= 3529) {
|
||||
winsize = 7;
|
||||
} else {
|
||||
winsize = 8;
|
||||
}
|
||||
|
||||
#ifdef MP_LOW_MEM
|
||||
if (winsize > 5) {
|
||||
winsize = 5;
|
||||
}
|
||||
#endif
|
||||
|
||||
/* init M array */
|
||||
/* init first cell */
|
||||
if ((err = mp_init(&M[1])) != MP_OKAY) {
|
||||
return err;
|
||||
}
|
||||
|
||||
/* now init the second half of the array */
|
||||
for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
|
||||
if ((err = mp_init(&M[x])) != MP_OKAY) {
|
||||
for (y = 1<<(winsize-1); y < x; y++) {
|
||||
mp_clear (&M[y]);
|
||||
}
|
||||
mp_clear(&M[1]);
|
||||
return err;
|
||||
}
|
||||
}
|
||||
|
||||
/* determine and setup reduction code */
|
||||
if (redmode == 0) {
|
||||
#ifdef BN_MP_MONTGOMERY_SETUP_C
|
||||
/* now setup montgomery */
|
||||
if ((err = mp_montgomery_setup (P, &mp)) != MP_OKAY) {
|
||||
goto LBL_M;
|
||||
}
|
||||
#else
|
||||
err = MP_VAL;
|
||||
goto LBL_M;
|
||||
#endif
|
||||
|
||||
/* automatically pick the comba one if available (saves quite a few calls/ifs) */
|
||||
#ifdef BN_FAST_MP_MONTGOMERY_REDUCE_C
|
||||
if (((P->used * 2 + 1) < MP_WARRAY) &&
|
||||
P->used < (1 << ((CHAR_BIT * sizeof (mp_word)) - (2 * DIGIT_BIT)))) {
|
||||
redux = fast_mp_montgomery_reduce;
|
||||
} else
|
||||
#endif
|
||||
{
|
||||
#ifdef BN_MP_MONTGOMERY_REDUCE_C
|
||||
/* use slower baseline Montgomery method */
|
||||
redux = mp_montgomery_reduce;
|
||||
#else
|
||||
err = MP_VAL;
|
||||
goto LBL_M;
|
||||
#endif
|
||||
}
|
||||
} else if (redmode == 1) {
|
||||
#if defined(BN_MP_DR_SETUP_C) && defined(BN_MP_DR_REDUCE_C)
|
||||
/* setup DR reduction for moduli of the form B**k - b */
|
||||
mp_dr_setup(P, &mp);
|
||||
redux = mp_dr_reduce;
|
||||
#else
|
||||
err = MP_VAL;
|
||||
goto LBL_M;
|
||||
#endif
|
||||
} else {
|
||||
#if defined(BN_MP_REDUCE_2K_SETUP_C) && defined(BN_MP_REDUCE_2K_C)
|
||||
/* setup DR reduction for moduli of the form 2**k - b */
|
||||
if ((err = mp_reduce_2k_setup(P, &mp)) != MP_OKAY) {
|
||||
goto LBL_M;
|
||||
}
|
||||
redux = mp_reduce_2k;
|
||||
#else
|
||||
err = MP_VAL;
|
||||
goto LBL_M;
|
||||
#endif
|
||||
}
|
||||
|
||||
/* setup result */
|
||||
if ((err = mp_init (&res)) != MP_OKAY) {
|
||||
goto LBL_M;
|
||||
}
|
||||
|
||||
/* create M table
|
||||
*
|
||||
|
||||
*
|
||||
* The first half of the table is not computed though accept for M[0] and M[1]
|
||||
*/
|
||||
|
||||
if (redmode == 0) {
|
||||
#ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_C
|
||||
/* now we need R mod m */
|
||||
if ((err = mp_montgomery_calc_normalization (&res, P)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
#else
|
||||
err = MP_VAL;
|
||||
goto LBL_RES;
|
||||
#endif
|
||||
|
||||
/* now set M[1] to G * R mod m */
|
||||
if ((err = mp_mulmod (G, &res, P, &M[1])) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
} else {
|
||||
mp_set(&res, 1);
|
||||
if ((err = mp_mod(G, P, &M[1])) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
|
||||
/* compute the value at M[1<<(winsize-1)] by squaring M[1] (winsize-1) times */
|
||||
if ((err = mp_copy (&M[1], &M[1 << (winsize - 1)])) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
|
||||
for (x = 0; x < (winsize - 1); x++) {
|
||||
if ((err = mp_sqr (&M[1 << (winsize - 1)], &M[1 << (winsize - 1)])) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&M[1 << (winsize - 1)], P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
|
||||
/* create upper table */
|
||||
for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
|
||||
if ((err = mp_mul (&M[x - 1], &M[1], &M[x])) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&M[x], P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
|
||||
/* set initial mode and bit cnt */
|
||||
mode = 0;
|
||||
bitcnt = 1;
|
||||
buf = 0;
|
||||
digidx = X->used - 1;
|
||||
bitcpy = 0;
|
||||
bitbuf = 0;
|
||||
|
||||
for (;;) {
|
||||
/* grab next digit as required */
|
||||
if (--bitcnt == 0) {
|
||||
/* if digidx == -1 we are out of digits so break */
|
||||
if (digidx == -1) {
|
||||
break;
|
||||
}
|
||||
/* read next digit and reset bitcnt */
|
||||
buf = X->dp[digidx--];
|
||||
bitcnt = (int)DIGIT_BIT;
|
||||
}
|
||||
|
||||
/* grab the next msb from the exponent */
|
||||
y = (mp_digit)(buf >> (DIGIT_BIT - 1)) & 1;
|
||||
buf <<= (mp_digit)1;
|
||||
|
||||
/* if the bit is zero and mode == 0 then we ignore it
|
||||
* These represent the leading zero bits before the first 1 bit
|
||||
* in the exponent. Technically this opt is not required but it
|
||||
* does lower the # of trivial squaring/reductions used
|
||||
*/
|
||||
if (mode == 0 && y == 0) {
|
||||
continue;
|
||||
}
|
||||
|
||||
/* if the bit is zero and mode == 1 then we square */
|
||||
if (mode == 1 && y == 0) {
|
||||
if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
continue;
|
||||
}
|
||||
|
||||
/* else we add it to the window */
|
||||
bitbuf |= (y << (winsize - ++bitcpy));
|
||||
mode = 2;
|
||||
|
||||
if (bitcpy == winsize) {
|
||||
/* ok window is filled so square as required and multiply */
|
||||
/* square first */
|
||||
for (x = 0; x < winsize; x++) {
|
||||
if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
|
||||
/* then multiply */
|
||||
if ((err = mp_mul (&res, &M[bitbuf], &res)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
|
||||
/* empty window and reset */
|
||||
bitcpy = 0;
|
||||
bitbuf = 0;
|
||||
mode = 1;
|
||||
}
|
||||
}
|
||||
|
||||
/* if bits remain then square/multiply */
|
||||
if (mode == 2 && bitcpy > 0) {
|
||||
/* square then multiply if the bit is set */
|
||||
for (x = 0; x < bitcpy; x++) {
|
||||
if ((err = mp_sqr (&res, &res)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
|
||||
/* get next bit of the window */
|
||||
bitbuf <<= 1;
|
||||
if ((bitbuf & (1 << winsize)) != 0) {
|
||||
/* then multiply */
|
||||
if ((err = mp_mul (&res, &M[1], &res)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
if ((err = redux (&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
if (redmode == 0) {
|
||||
/* fixup result if Montgomery reduction is used
|
||||
* recall that any value in a Montgomery system is
|
||||
* actually multiplied by R mod n. So we have
|
||||
* to reduce one more time to cancel out the factor
|
||||
* of R.
|
||||
*/
|
||||
if ((err = redux(&res, P, mp)) != MP_OKAY) {
|
||||
goto LBL_RES;
|
||||
}
|
||||
}
|
||||
|
||||
/* swap res with Y */
|
||||
mp_exch (&res, Y);
|
||||
err = MP_OKAY;
|
||||
LBL_RES:mp_clear (&res);
|
||||
LBL_M:
|
||||
mp_clear(&M[1]);
|
||||
for (x = 1<<(winsize-1); x < (1 << winsize); x++) {
|
||||
mp_clear (&M[x]);
|
||||
}
|
||||
return err;
|
||||
}
|
||||
#endif
|
||||
|
||||
|
||||
/* $Source: /cvs/libtom/libtommath/bn_mp_exptmod_fast.c,v $ */
|
||||
/* $Revision: 1.4 $ */
|
||||
/* $Date: 2006/12/28 01:25:13 $ */
|
||||
Reference in New Issue
Block a user