172 lines
3.3 KiB
C
172 lines
3.3 KiB
C
/*
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* Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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*/
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#include "internal/cryptlib.h"
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#include "bn_local.h"
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/* signed add of b to a. */
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int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
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{
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int ret, r_neg, cmp_res;
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bn_check_top(a);
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bn_check_top(b);
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if (a->neg == b->neg) {
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r_neg = a->neg;
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ret = BN_uadd(r, a, b);
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} else {
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cmp_res = BN_ucmp(a, b);
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if (cmp_res > 0) {
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r_neg = a->neg;
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ret = BN_usub(r, a, b);
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} else if (cmp_res < 0) {
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r_neg = b->neg;
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ret = BN_usub(r, b, a);
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} else {
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r_neg = 0;
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BN_zero(r);
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ret = 1;
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}
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}
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r->neg = r_neg;
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bn_check_top(r);
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return ret;
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}
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/* signed sub of b from a. */
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int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
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{
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int ret, r_neg, cmp_res;
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bn_check_top(a);
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bn_check_top(b);
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if (a->neg != b->neg) {
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r_neg = a->neg;
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ret = BN_uadd(r, a, b);
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} else {
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cmp_res = BN_ucmp(a, b);
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if (cmp_res > 0) {
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r_neg = a->neg;
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ret = BN_usub(r, a, b);
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} else if (cmp_res < 0) {
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r_neg = !b->neg;
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ret = BN_usub(r, b, a);
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} else {
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r_neg = 0;
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BN_zero(r);
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ret = 1;
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}
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}
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r->neg = r_neg;
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bn_check_top(r);
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return ret;
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}
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/* unsigned add of b to a, r can be equal to a or b. */
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int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
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{
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int max, min, dif;
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const BN_ULONG *ap, *bp;
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BN_ULONG *rp, carry, t1, t2;
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bn_check_top(a);
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bn_check_top(b);
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if (a->top < b->top) {
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const BIGNUM *tmp;
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tmp = a;
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a = b;
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b = tmp;
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}
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max = a->top;
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min = b->top;
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dif = max - min;
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if (bn_wexpand(r, max + 1) == NULL)
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return 0;
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r->top = max;
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ap = a->d;
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bp = b->d;
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rp = r->d;
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carry = bn_add_words(rp, ap, bp, min);
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rp += min;
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ap += min;
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while (dif) {
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dif--;
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t1 = *(ap++);
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t2 = (t1 + carry) & BN_MASK2;
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*(rp++) = t2;
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carry &= (t2 == 0);
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}
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*rp = carry;
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r->top += carry;
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r->neg = 0;
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bn_check_top(r);
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return 1;
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}
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/* unsigned subtraction of b from a, a must be larger than b. */
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int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
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{
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int max, min, dif;
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BN_ULONG t1, t2, borrow, *rp;
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const BN_ULONG *ap, *bp;
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bn_check_top(a);
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bn_check_top(b);
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max = a->top;
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min = b->top;
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dif = max - min;
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if (dif < 0) { /* hmm... should not be happening */
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ERR_raise(ERR_LIB_BN, BN_R_ARG2_LT_ARG3);
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return 0;
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}
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if (bn_wexpand(r, max) == NULL)
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return 0;
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ap = a->d;
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bp = b->d;
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rp = r->d;
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borrow = bn_sub_words(rp, ap, bp, min);
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ap += min;
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rp += min;
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while (dif) {
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dif--;
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t1 = *(ap++);
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t2 = (t1 - borrow) & BN_MASK2;
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*(rp++) = t2;
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borrow &= (t1 == 0);
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}
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while (max && *--rp == 0)
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max--;
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r->top = max;
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r->neg = 0;
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bn_pollute(r);
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return 1;
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}
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