Coverage Report

Created: 2024-11-21 07:03

/src/openssl/crypto/bn/bn_mod.c
Line
Count
Source (jump to first uncovered line)
1
/*
2
 * Copyright 1998-2024 The OpenSSL Project Authors. All Rights Reserved.
3
 *
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
8
 */
9
10
#include "internal/cryptlib.h"
11
#include "internal/nelem.h"
12
#include "bn_local.h"
13
14
int BN_nnmod(BIGNUM *r, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)
15
661k
{
16
    /*
17
     * like BN_mod, but returns non-negative remainder (i.e., 0 <= r < |d|
18
     * always holds)
19
     */
20
21
661k
    if (r == d) {
22
5
        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_INVALID_ARGUMENT);
23
5
        return 0;
24
5
    }
25
26
661k
    if (!(BN_mod(r, m, d, ctx)))
27
53
        return 0;
28
660k
    if (!r->neg)
29
628k
        return 1;
30
    /* now   -|d| < r < 0,  so we have to set  r := r + |d| */
31
32.1k
    return (d->neg ? BN_sub : BN_add) (r, r, d);
32
660k
}
33
34
int BN_mod_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
35
               BN_CTX *ctx)
36
89
{
37
89
    if (!BN_add(r, a, b))
38
0
        return 0;
39
89
    return BN_nnmod(r, r, m, ctx);
40
89
}
41
42
/*
43
 * BN_mod_add variant that may be used if both a and b are non-negative and
44
 * less than m. The original algorithm was
45
 *
46
 *    if (!BN_uadd(r, a, b))
47
 *       return 0;
48
 *    if (BN_ucmp(r, m) >= 0)
49
 *       return BN_usub(r, r, m);
50
 *
51
 * which is replaced with addition, subtracting modulus, and conditional
52
 * move depending on whether or not subtraction borrowed.
53
 */
54
int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
55
                         const BIGNUM *m)
56
2.11M
{
57
2.11M
    size_t i, ai, bi, mtop = m->top;
58
2.11M
    BN_ULONG storage[1024 / BN_BITS2];
59
2.11M
    BN_ULONG carry, temp, mask, *rp, *tp = storage;
60
2.11M
    const BN_ULONG *ap, *bp;
61
62
2.11M
    if (bn_wexpand(r, mtop) == NULL)
63
0
        return 0;
64
65
2.11M
    if (mtop > OSSL_NELEM(storage)) {
66
108
        tp = OPENSSL_malloc(mtop * sizeof(BN_ULONG));
67
108
        if (tp == NULL)
68
0
            return 0;
69
108
    }
70
71
2.11M
    ap = a->d != NULL ? a->d : tp;
72
2.11M
    bp = b->d != NULL ? b->d : tp;
73
74
14.1M
    for (i = 0, ai = 0, bi = 0, carry = 0; i < mtop;) {
75
12.0M
        mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
76
12.0M
        temp = ((ap[ai] & mask) + carry) & BN_MASK2;
77
12.0M
        carry = (temp < carry);
78
79
12.0M
        mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
80
12.0M
        tp[i] = ((bp[bi] & mask) + temp) & BN_MASK2;
81
12.0M
        carry += (tp[i] < temp);
82
83
12.0M
        i++;
84
12.0M
        ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
85
12.0M
        bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
86
12.0M
    }
87
2.11M
    rp = r->d;
88
2.11M
    carry -= bn_sub_words(rp, tp, m->d, mtop);
89
14.1M
    for (i = 0; i < mtop; i++) {
90
12.0M
        rp[i] = (carry & tp[i]) | (~carry & rp[i]);
91
12.0M
        ((volatile BN_ULONG *)tp)[i] = 0;
92
12.0M
    }
93
2.11M
    r->top = mtop;
94
2.11M
    r->flags |= BN_FLG_FIXED_TOP;
95
2.11M
    r->neg = 0;
96
97
2.11M
    if (tp != storage)
98
108
        OPENSSL_free(tp);
99
100
2.11M
    return 1;
101
2.11M
}
102
103
int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
104
                     const BIGNUM *m)
105
2.11M
{
106
2.11M
    int ret = bn_mod_add_fixed_top(r, a, b, m);
107
108
2.11M
    if (ret)
109
2.11M
        bn_correct_top(r);
110
111
2.11M
    return ret;
112
2.11M
}
113
114
int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
115
               BN_CTX *ctx)
116
143
{
117
143
    if (!BN_sub(r, a, b))
118
0
        return 0;
119
143
    return BN_nnmod(r, r, m, ctx);
120
143
}
121
122
/*
123
 * BN_mod_sub variant that may be used if both a and b are non-negative,
124
 * a is less than m, while b is of same bit width as m. It's implemented
125
 * as subtraction followed by two conditional additions.
126
 *
127
 * 0 <= a < m
128
 * 0 <= b < 2^w < 2*m
129
 *
130
 * after subtraction
131
 *
132
 * -2*m < r = a - b < m
133
 *
134
 * Thus it takes up to two conditional additions to make |r| positive.
135
 */
136
int bn_mod_sub_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
137
                         const BIGNUM *m)
138
0
{
139
0
    size_t i, ai, bi, mtop = m->top;
140
0
    BN_ULONG borrow, carry, ta, tb, mask, *rp;
141
0
    const BN_ULONG *ap, *bp;
142
143
0
    if (bn_wexpand(r, mtop) == NULL)
144
0
        return 0;
145
146
0
    rp = r->d;
147
0
    ap = a->d != NULL ? a->d : rp;
148
0
    bp = b->d != NULL ? b->d : rp;
149
150
0
    for (i = 0, ai = 0, bi = 0, borrow = 0; i < mtop;) {
151
0
        mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1));
152
0
        ta = ap[ai] & mask;
153
154
0
        mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1));
155
0
        tb = bp[bi] & mask;
156
0
        rp[i] = ta - tb - borrow;
157
0
        if (ta != tb)
158
0
            borrow = (ta < tb);
159
160
0
        i++;
161
0
        ai += (i - a->dmax) >> (8 * sizeof(i) - 1);
162
0
        bi += (i - b->dmax) >> (8 * sizeof(i) - 1);
163
0
    }
164
0
    ap = m->d;
165
0
    for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
166
0
        ta = ((ap[i] & mask) + carry) & BN_MASK2;
167
0
        carry = (ta < carry);
168
0
        rp[i] = (rp[i] + ta) & BN_MASK2;
169
0
        carry += (rp[i] < ta);
170
0
    }
171
0
    borrow -= carry;
172
0
    for (i = 0, mask = 0 - borrow, carry = 0; i < mtop; i++) {
173
0
        ta = ((ap[i] & mask) + carry) & BN_MASK2;
174
0
        carry = (ta < carry);
175
0
        rp[i] = (rp[i] + ta) & BN_MASK2;
176
0
        carry += (rp[i] < ta);
177
0
    }
178
179
0
    r->top = mtop;
180
0
    r->flags |= BN_FLG_FIXED_TOP;
181
0
    r->neg = 0;
182
183
0
    return 1;
184
0
}
185
186
/*
187
 * BN_mod_sub variant that may be used if both a and b are non-negative and
188
 * less than m
189
 */
190
int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
191
                     const BIGNUM *m)
192
2.30M
{
193
2.30M
    if (r == m) {
194
0
        ERR_raise(ERR_LIB_BN, ERR_R_PASSED_INVALID_ARGUMENT);
195
0
        return 0;
196
0
    }
197
198
2.30M
    if (!BN_sub(r, a, b))
199
0
        return 0;
200
2.30M
    if (r->neg)
201
1.13M
        return BN_add(r, r, m);
202
1.16M
    return 1;
203
2.30M
}
204
205
/* slow but works */
206
int BN_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
207
               BN_CTX *ctx)
208
355k
{
209
355k
    BIGNUM *t;
210
355k
    int ret = 0;
211
212
355k
    bn_check_top(a);
213
355k
    bn_check_top(b);
214
355k
    bn_check_top(m);
215
216
355k
    BN_CTX_start(ctx);
217
355k
    if ((t = BN_CTX_get(ctx)) == NULL)
218
0
        goto err;
219
355k
    if (a == b) {
220
314k
        if (!BN_sqr(t, a, ctx))
221
0
            goto err;
222
314k
    } else {
223
40.6k
        if (!BN_mul(t, a, b, ctx))
224
0
            goto err;
225
40.6k
    }
226
355k
    if (!BN_nnmod(r, t, m, ctx))
227
29
        goto err;
228
355k
    bn_check_top(r);
229
355k
    ret = 1;
230
355k
 err:
231
355k
    BN_CTX_end(ctx);
232
355k
    return ret;
233
355k
}
234
235
int BN_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
236
952
{
237
952
    if (!BN_sqr(r, a, ctx))
238
0
        return 0;
239
    /* r->neg == 0,  thus we don't need BN_nnmod */
240
952
    return BN_mod(r, r, m, ctx);
241
952
}
242
243
int BN_mod_lshift1(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
244
0
{
245
0
    if (!BN_lshift1(r, a))
246
0
        return 0;
247
0
    bn_check_top(r);
248
0
    return BN_nnmod(r, r, m, ctx);
249
0
}
250
251
/*
252
 * BN_mod_lshift1 variant that may be used if a is non-negative and less than
253
 * m
254
 */
255
int BN_mod_lshift1_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *m)
256
851k
{
257
851k
    if (!BN_lshift1(r, a))
258
0
        return 0;
259
851k
    bn_check_top(r);
260
851k
    if (BN_cmp(r, m) >= 0)
261
424k
        return BN_sub(r, r, m);
262
426k
    return 1;
263
851k
}
264
265
int BN_mod_lshift(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m,
266
                  BN_CTX *ctx)
267
2
{
268
2
    BIGNUM *abs_m = NULL;
269
2
    int ret;
270
271
2
    if (!BN_nnmod(r, a, m, ctx))
272
0
        return 0;
273
274
2
    if (m->neg) {
275
0
        abs_m = BN_dup(m);
276
0
        if (abs_m == NULL)
277
0
            return 0;
278
0
        abs_m->neg = 0;
279
0
    }
280
281
2
    ret = BN_mod_lshift_quick(r, r, n, (abs_m ? abs_m : m));
282
2
    bn_check_top(r);
283
284
2
    BN_free(abs_m);
285
2
    return ret;
286
2
}
287
288
/*
289
 * BN_mod_lshift variant that may be used if a is non-negative and less than
290
 * m
291
 */
292
int BN_mod_lshift_quick(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m)
293
441k
{
294
441k
    if (r != a) {
295
379k
        if (BN_copy(r, a) == NULL)
296
0
            return 0;
297
379k
    }
298
299
1.22M
    while (n > 0) {
300
785k
        int max_shift;
301
302
        /* 0 < r < m */
303
785k
        max_shift = BN_num_bits(m) - BN_num_bits(r);
304
        /* max_shift >= 0 */
305
306
785k
        if (max_shift < 0) {
307
0
            ERR_raise(ERR_LIB_BN, BN_R_INPUT_NOT_REDUCED);
308
0
            return 0;
309
0
        }
310
311
785k
        if (max_shift > n)
312
109k
            max_shift = n;
313
314
785k
        if (max_shift) {
315
389k
            if (!BN_lshift(r, r, max_shift))
316
0
                return 0;
317
389k
            n -= max_shift;
318
396k
        } else {
319
396k
            if (!BN_lshift1(r, r))
320
0
                return 0;
321
396k
            --n;
322
396k
        }
323
324
        /* BN_num_bits(r) <= BN_num_bits(m) */
325
326
785k
        if (BN_cmp(r, m) >= 0) {
327
434k
            if (!BN_sub(r, r, m))
328
0
                return 0;
329
434k
        }
330
785k
    }
331
441k
    bn_check_top(r);
332
333
441k
    return 1;
334
441k
}