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Don't use windowed exponentiation for small public exponents. 

Speeds up public key operations.  Path contributed by
    Sheueling Chang Shantz <sheueling.chang@sun.com>,
    Stephen Fung <stephen.fung@sun.com>, and
    Douglas Stebila <douglas@stebila.ca> of Sun Laboratories.
This commit is contained in:
nelsonb%netscape.com 2003-09-26 02:15:12 +00:00
Родитель 386b7fa766
Коммит 3ec40f0ab7
1 изменённых файлов: 31 добавлений и 4 удалений
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35
security/nss/lib/freebl/mpi/mpmontg.c
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@ -15,8 +15,14 @@
* Communications Corporation. Portions created by Netscape are
* Copyright (C) 2000 Netscape Communications Corporation. All
* Rights Reserved.
*
* Portions created by Sun Microsystems, Inc. are Copyright (C) 2003
* Sun Microsystems, Inc. All Rights Reserved.
*
* Contributor(s):
* Sheueling Chang Shantz <sheueling.chang@sun.com>,
* Stephen Fung <stephen.fung@sun.com>, and
* Douglas Stebila <douglas@stebila.ca> of Sun Laboratories.
*
* Alternatively, the contents of this file may be used under the
* terms of the GNU General Public License Version 2 or later (the
@ -29,7 +35,7 @@
* the GPL. If you do not delete the provisions above, a recipient
* may use your version of this file under either the MPL or the
* GPL.
* $Id: mpmontg.c,v 1.11 2002/04/04 00:19:43 nelsonb%netscape.com Exp $
* $Id: mpmontg.c,v 1.12 2003/09/26 02:15:12 nelsonb%netscape.com Exp $
*/
/* This file implements moduluar exponentiation using Montgomery's
@ -266,7 +272,15 @@ mp_err mp_exptmod_f(const mp_int * montBase,
MP_CHECKOK( mpl_get_bits(exponent, expOff, window_bits) );
smallExp = (mp_size)res;
if (window_bits == 4) {
if (window_bits == 1) {
if (!smallExp) {
SQR;
} else if (smallExp & 1) {
SQR; MUL(0);
} else {
ABORT;
}
} else if (window_bits == 4) {
if (!smallExp) {
SQR; SQR; SQR; SQR;
} else if (smallExp & 1) {
@ -406,7 +420,15 @@ mp_err mp_exptmod_i(const mp_int * montBase,
MP_CHECKOK( mpl_get_bits(exponent, expOff, window_bits) );
smallExp = (mp_size)res;
if (window_bits == 4) {
if (window_bits == 1) {
if (!smallExp) {
SQR(pa1,pa2); SWAPPA;
} else if (smallExp & 1) {
SQR(pa1,pa2); MUL(0,pa2,pa1);
} else {
ABORT;
}
} else if (window_bits == 4) {
if (!smallExp) {
SQR(pa1,pa2); SQR(pa2,pa1); SQR(pa1,pa2); SQR(pa2,pa1);
} else if (smallExp & 1) {
@ -538,8 +560,13 @@ mp_err mp_exptmod(const mp_int *inBase, const mp_int *exponent,
window_bits = 6;
else if (bits_in_exponent > 160)
window_bits = 5;
else
else if (bits_in_exponent > 20)
window_bits = 4;
/* RSA public key exponents are typically under 20 bits (common values
* are: 3, 17, 65537) and a 4-bit window is inefficient
*/
else
window_bits = 1;
odd_ints = 1 << (window_bits - 1);
i = bits_in_exponent % window_bits;
if (i != 0) {