2 * Copyright 1998-2016 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the OpenSSL license (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))) == NULL)
63 ap = a->d != NULL ? a->d : tp;
64 bp = b->d != NULL ? b->d : tp;
66 for (i = 0, ai = 0, bi = 0, carry = 0; i < mtop;) {
67 mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
68 temp = ((ap[ai] & mask) + carry) & BN_MASK2;
69 carry = (temp < carry);
71 mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
72 tp[i] = ((bp[bi] & mask) + temp) & BN_MASK2;
73 carry += (tp[i] < temp);
76 ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
77 bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
80 carry -= bn_sub_words(rp, tp, m->d, mtop);
81 for (i = 0; i < mtop; i++) {
82 rp[i] = (carry & tp[i]) | (~carry & rp[i]);
83 ((volatile BN_ULONG *)tp)[i] = 0;
93 int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
96 int ret = bn_mod_add_fixed_top(r, a, b, m);
104 int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
107 if (!BN_sub(r, a, b))
109 return BN_nnmod(r, r, m, ctx);
113 * BN_mod_sub variant that may be used if both a and b are non-negative and
116 int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
119 if (!BN_sub(r, a, b))
122 return BN_add(r, r, m);
127 int BN_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
138 if ((t = BN_CTX_get(ctx)) == NULL)
141 if (!BN_sqr(t, a, ctx))
144 if (!BN_mul(t, a, b, ctx))
147 if (!BN_nnmod(r, t, m, ctx))
156 int BN_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
158 if (!BN_sqr(r, a, ctx))
160 /* r->neg == 0, thus we don't need BN_nnmod */
161 return BN_mod(r, r, m, ctx);
164 int BN_mod_lshift1(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
166 if (!BN_lshift1(r, a))
169 return BN_nnmod(r, r, m, ctx);
173 * BN_mod_lshift1 variant that may be used if a is non-negative and less than
176 int BN_mod_lshift1_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *m)
178 if (!BN_lshift1(r, a))
181 if (BN_cmp(r, m) >= 0)
182 return BN_sub(r, r, m);
186 int BN_mod_lshift(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m,
189 BIGNUM *abs_m = NULL;
192 if (!BN_nnmod(r, a, m, ctx))
202 ret = BN_mod_lshift_quick(r, r, n, (abs_m ? abs_m : m));
210 * BN_mod_lshift variant that may be used if a is non-negative and less than
213 int BN_mod_lshift_quick(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m)
216 if (BN_copy(r, a) == NULL)
224 max_shift = BN_num_bits(m) - BN_num_bits(r);
228 BNerr(BN_F_BN_MOD_LSHIFT_QUICK, BN_R_INPUT_NOT_REDUCED);
236 if (!BN_lshift(r, r, max_shift))
240 if (!BN_lshift1(r, r))
245 /* BN_num_bits(r) <= BN_num_bits(m) */
247 if (BN_cmp(r, m) >= 0) {
248 if (!BN_sub(r, r, m))