2 * Copyright 1998-2021 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
10 #include "internal/cryptlib.h"
13 int BN_nnmod(BIGNUM *r, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)
16 * like BN_mod, but returns non-negative remainder (i.e., 0 <= r < |d|
20 if (!(BN_mod(r, m, d, ctx)))
24 /* now -|d| < r < 0, so we have to set r := r + |d| */
25 return (d->neg ? BN_sub : BN_add) (r, r, d);
28 int BN_mod_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
33 return BN_nnmod(r, r, m, ctx);
37 * BN_mod_add variant that may be used if both a and b are non-negative and
38 * less than m. The original algorithm was
40 * if (!BN_uadd(r, a, b))
42 * if (BN_ucmp(r, m) >= 0)
43 * return BN_usub(r, r, m);
45 * which is replaced with addition, subtracting modulus, and conditional
46 * move depending on whether or not subtraction borrowed.
48 int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
51 size_t i, ai, bi, mtop = m->top;
52 BN_ULONG storage[1024 / BN_BITS2];
53 BN_ULONG carry, temp, mask, *rp, *tp = storage;
54 const BN_ULONG *ap, *bp;
56 if (bn_wexpand(r, mtop) == NULL)
59 if (mtop > sizeof(storage) / sizeof(storage[0])) {
60 tp = OPENSSL_malloc(mtop * sizeof(BN_ULONG));
62 ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
67 ap = a->d != NULL ? a->d : tp;
68 bp = b->d != NULL ? b->d : tp;
70 for (i = 0, ai = 0, bi = 0, carry = 0; i < mtop;) {
71 mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
72 temp = ((ap[ai] & mask) + carry) & BN_MASK2;
73 carry = (temp < carry);
75 mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
76 tp[i] = ((bp[bi] & mask) + temp) & BN_MASK2;
77 carry += (tp[i] < temp);
80 ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
81 bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
84 carry -= bn_sub_words(rp, tp, m->d, mtop);
85 for (i = 0; i < mtop; i++) {
86 rp[i] = (carry & tp[i]) | (~carry & rp[i]);
87 ((volatile BN_ULONG *)tp)[i] = 0;
90 r->flags |= BN_FLG_FIXED_TOP;
99 int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
102 int ret = bn_mod_add_fixed_top(r, a, b, m);
110 int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
113 if (!BN_sub(r, a, b))
115 return BN_nnmod(r, r, m, ctx);
119 * BN_mod_sub variant that may be used if both a and b are non-negative,
120 * a is less than m, while b is of same bit width as m. It's implemented
121 * as subtraction followed by two conditional additions.
128 * -2*m < r = a - b < m
130 * Thus it takes up to two conditional additions to make |r| positive.
132 int bn_mod_sub_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
135 size_t i, ai, bi, mtop = m->top;
136 BN_ULONG borrow, carry, ta, tb, mask, *rp;
137 const BN_ULONG *ap, *bp;
139 if (bn_wexpand(r, mtop) == NULL)
143 ap = a->d != NULL ? a->d : rp;
144 bp = b->d != NULL ? b->d : rp;
146 for (i = 0, ai = 0, bi = 0, borrow = 0; i < mtop;) {
147 mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
150 mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
152 rp[i] = ta - tb - borrow;
157 ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
158 bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
161 for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
162 ta = ((ap[i] & mask) + carry) & BN_MASK2;
163 carry = (ta < carry);
164 rp[i] = (rp[i] + ta) & BN_MASK2;
165 carry += (rp[i] < ta);
168 for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
169 ta = ((ap[i] & mask) + carry) & BN_MASK2;
170 carry = (ta < carry);
171 rp[i] = (rp[i] + ta) & BN_MASK2;
172 carry += (rp[i] < ta);
176 r->flags |= BN_FLG_FIXED_TOP;
183 * BN_mod_sub variant that may be used if both a and b are non-negative and
186 int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
189 if (!BN_sub(r, a, b))
192 return BN_add(r, r, m);
197 int BN_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
208 if ((t = BN_CTX_get(ctx)) == NULL)
211 if (!BN_sqr(t, a, ctx))
214 if (!BN_mul(t, a, b, ctx))
217 if (!BN_nnmod(r, t, m, ctx))
226 int BN_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
228 if (!BN_sqr(r, a, ctx))
230 /* r->neg == 0, thus we don't need BN_nnmod */
231 return BN_mod(r, r, m, ctx);
234 int BN_mod_lshift1(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
236 if (!BN_lshift1(r, a))
239 return BN_nnmod(r, r, m, ctx);
243 * BN_mod_lshift1 variant that may be used if a is non-negative and less than
246 int BN_mod_lshift1_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *m)
248 if (!BN_lshift1(r, a))
251 if (BN_cmp(r, m) >= 0)
252 return BN_sub(r, r, m);
256 int BN_mod_lshift(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m,
259 BIGNUM *abs_m = NULL;
262 if (!BN_nnmod(r, a, m, ctx))
272 ret = BN_mod_lshift_quick(r, r, n, (abs_m ? abs_m : m));
280 * BN_mod_lshift variant that may be used if a is non-negative and less than
283 int BN_mod_lshift_quick(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m)
286 if (BN_copy(r, a) == NULL)
294 max_shift = BN_num_bits(m) - BN_num_bits(r);
298 ERR_raise(ERR_LIB_BN, BN_R_INPUT_NOT_REDUCED);
306 if (!BN_lshift(r, r, max_shift))
310 if (!BN_lshift1(r, r))
315 /* BN_num_bits(r) <= BN_num_bits(m) */
317 if (BN_cmp(r, m) >= 0) {
318 if (!BN_sub(r, r, m))