/src/openssl36/crypto/ec/ecp_mont.c

Source
/*
 * Copyright 2001-2025 The OpenSSL Project Authors. All Rights Reserved.
 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
 *
 * Licensed under the Apache License 2.0 (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

/*
 * ECDSA low-level APIs are deprecated for public use, but still ok for
 * internal use.
 */
#include "internal/deprecated.h"

#include <openssl/err.h>

#include "ec_local.h"

const EC_METHOD *EC_GFp_mont_method(void)
{
    static const EC_METHOD ret = {
        EC_FLAGS_DEFAULT_OCT,
        NID_X9_62_prime_field,
        ossl_ec_GFp_mont_group_init,
        ossl_ec_GFp_mont_group_finish,
        ossl_ec_GFp_mont_group_clear_finish,
        ossl_ec_GFp_mont_group_copy,
        ossl_ec_GFp_mont_group_set_curve,
        ossl_ec_GFp_simple_group_get_curve,
        ossl_ec_GFp_simple_group_get_degree,
        ossl_ec_group_simple_order_bits,
        ossl_ec_GFp_simple_group_check_discriminant,
        ossl_ec_GFp_simple_point_init,
        ossl_ec_GFp_simple_point_finish,
        ossl_ec_GFp_simple_point_clear_finish,
        ossl_ec_GFp_simple_point_copy,
        ossl_ec_GFp_simple_point_set_to_infinity,
        ossl_ec_GFp_simple_point_set_affine_coordinates,
        ossl_ec_GFp_simple_point_get_affine_coordinates,
        0, 0, 0,
        ossl_ec_GFp_simple_add,
        ossl_ec_GFp_simple_dbl,
        ossl_ec_GFp_simple_invert,
        ossl_ec_GFp_simple_is_at_infinity,
        ossl_ec_GFp_simple_is_on_curve,
        ossl_ec_GFp_simple_cmp,
        ossl_ec_GFp_simple_make_affine,
        ossl_ec_GFp_simple_points_make_affine,
        0 /* mul */,
        0 /* precompute_mult */,
        0 /* have_precompute_mult */,
        ossl_ec_GFp_mont_field_mul,
        ossl_ec_GFp_mont_field_sqr,
        0 /* field_div */,
        ossl_ec_GFp_mont_field_inv,
        ossl_ec_GFp_mont_field_encode,
        ossl_ec_GFp_mont_field_decode,
        ossl_ec_GFp_mont_field_set_to_one,
        ossl_ec_key_simple_priv2oct,
        ossl_ec_key_simple_oct2priv,
        0, /* set private */
        ossl_ec_key_simple_generate_key,
        ossl_ec_key_simple_check_key,
        ossl_ec_key_simple_generate_public_key,
        0, /* keycopy */
        0, /* keyfinish */
        ossl_ecdh_simple_compute_key,
        ossl_ecdsa_simple_sign_setup,
        ossl_ecdsa_simple_sign_sig,
        ossl_ecdsa_simple_verify_sig,
        0, /* field_inverse_mod_ord */
        ossl_ec_GFp_simple_blind_coordinates,
        ossl_ec_GFp_simple_ladder_pre,
        ossl_ec_GFp_simple_ladder_step,
        ossl_ec_GFp_simple_ladder_post
    };

    return &ret;
}

int ossl_ec_GFp_mont_group_init(EC_GROUP *group)
{
    int ok;

    ok = ossl_ec_GFp_simple_group_init(group);
    group->field_data1 = NULL;
    group->field_data2 = NULL;
    return ok;
}

void ossl_ec_GFp_mont_group_finish(EC_GROUP *group)
{
    BN_MONT_CTX_free(group->field_data1);
    group->field_data1 = NULL;
    BN_free(group->field_data2);
    group->field_data2 = NULL;
    ossl_ec_GFp_simple_group_finish(group);
}

void ossl_ec_GFp_mont_group_clear_finish(EC_GROUP *group)
{
    BN_MONT_CTX_free(group->field_data1);
    group->field_data1 = NULL;
    BN_clear_free(group->field_data2);
    group->field_data2 = NULL;
    ossl_ec_GFp_simple_group_clear_finish(group);
}

int ossl_ec_GFp_mont_group_copy(EC_GROUP *dest, const EC_GROUP *src)
{
    BN_MONT_CTX_free(dest->field_data1);
    dest->field_data1 = NULL;
    BN_clear_free(dest->field_data2);
    dest->field_data2 = NULL;

    if (!ossl_ec_GFp_simple_group_copy(dest, src))
        return 0;

    if (src->field_data1 != NULL) {
        dest->field_data1 = BN_MONT_CTX_new();
        if (dest->field_data1 == NULL)
            return 0;
        if (!BN_MONT_CTX_copy(dest->field_data1, src->field_data1))
            goto err;
    }
    if (src->field_data2 != NULL) {
        dest->field_data2 = BN_dup(src->field_data2);
        if (dest->field_data2 == NULL)
            goto err;
    }

    return 1;

err:
    BN_MONT_CTX_free(dest->field_data1);
    dest->field_data1 = NULL;
    return 0;
}

int ossl_ec_GFp_mont_group_set_curve(EC_GROUP *group, const BIGNUM *p,
    const BIGNUM *a, const BIGNUM *b,
    BN_CTX *ctx)
{
    BN_CTX *new_ctx = NULL;
    BN_MONT_CTX *mont = NULL;
    BIGNUM *one = NULL;
    int ret = 0;

    BN_MONT_CTX_free(group->field_data1);
    group->field_data1 = NULL;
    BN_free(group->field_data2);
    group->field_data2 = NULL;

    if (ctx == NULL) {
        ctx = new_ctx = BN_CTX_new_ex(group->libctx);
        if (ctx == NULL)
            return 0;
    }

    mont = BN_MONT_CTX_new();
    if (mont == NULL)
        goto err;
    if (!BN_MONT_CTX_set(mont, p, ctx)) {
        ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
        goto err;
    }
    one = BN_new();
    if (one == NULL)
        goto err;
    if (!BN_to_montgomery(one, BN_value_one(), mont, ctx))
        goto err;

    group->field_data1 = mont;
    mont = NULL;
    group->field_data2 = one;
    one = NULL;

    ret = ossl_ec_GFp_simple_group_set_curve(group, p, a, b, ctx);

    if (!ret) {
        BN_MONT_CTX_free(group->field_data1);
        group->field_data1 = NULL;
        BN_free(group->field_data2);
        group->field_data2 = NULL;
    }

err:
    BN_free(one);
    BN_CTX_free(new_ctx);
    BN_MONT_CTX_free(mont);
    return ret;
}

int ossl_ec_GFp_mont_field_mul(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
    const BIGNUM *b, BN_CTX *ctx)
{
    if (group->field_data1 == NULL) {
        ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
        return 0;
    }

    return BN_mod_mul_montgomery(r, a, b, group->field_data1, ctx);
}

int ossl_ec_GFp_mont_field_sqr(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
    BN_CTX *ctx)
{
    if (group->field_data1 == NULL) {
        ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
        return 0;
    }

    return BN_mod_mul_montgomery(r, a, a, group->field_data1, ctx);
}

/*-
 * Computes the multiplicative inverse of a in GF(p), storing the result in r.
 * If a is zero (or equivalent), you'll get an EC_R_CANNOT_INVERT error.
 * We have a Mont structure, so SCA hardening is FLT inversion.
 */
int ossl_ec_GFp_mont_field_inv(const EC_GROUP *group, BIGNUM *r, const BIGNUM *a,
    BN_CTX *ctx)
{
    BIGNUM *e = NULL;
    BN_CTX *new_ctx = NULL;
    int ret = 0;

    if (group->field_data1 == NULL)
        return 0;

    if (ctx == NULL
        && (ctx = new_ctx = BN_CTX_secure_new_ex(group->libctx)) == NULL)
        return 0;

    BN_CTX_start(ctx);
    if ((e = BN_CTX_get(ctx)) == NULL)
        goto err;

    /* Inverse in constant time with Fermats Little Theorem */
    if (!BN_set_word(e, 2))
        goto err;
    if (!BN_sub(e, group->field, e))
        goto err;
    /*-
     * Exponent e is public.
     * No need for scatter-gather or BN_FLG_CONSTTIME.
     */
    if (!BN_mod_exp_mont(r, a, e, group->field, ctx, group->field_data1))
        goto err;

    /* throw an error on zero */
    if (BN_is_zero(r)) {
        ERR_raise(ERR_LIB_EC, EC_R_CANNOT_INVERT);
        goto err;
    }

    ret = 1;

err:
    BN_CTX_end(ctx);
    BN_CTX_free(new_ctx);
    return ret;
}

int ossl_ec_GFp_mont_field_encode(const EC_GROUP *group, BIGNUM *r,
    const BIGNUM *a, BN_CTX *ctx)
{
    if (group->field_data1 == NULL) {
        ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
        return 0;
    }

    return BN_to_montgomery(r, a, (BN_MONT_CTX *)group->field_data1, ctx);
}

int ossl_ec_GFp_mont_field_decode(const EC_GROUP *group, BIGNUM *r,
    const BIGNUM *a, BN_CTX *ctx)
{
    if (group->field_data1 == NULL) {
        ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
        return 0;
    }

    return BN_from_montgomery(r, a, group->field_data1, ctx);
}

int ossl_ec_GFp_mont_field_set_to_one(const EC_GROUP *group, BIGNUM *r,
    BN_CTX *ctx)
{
    if (group->field_data2 == NULL) {
        ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
        return 0;
    }

    if (!BN_copy(r, group->field_data2))
        return 0;
    return 1;
}

Coverage Report

Created: 2026-07-23 06:28

Line	Count	Source
1		/*
2		* Copyright 2001-2025 The OpenSSL Project Authors. All Rights Reserved.
3		* Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
4		*
5		* Licensed under the Apache License 2.0 (the "License"). You may not use
6		* this file except in compliance with the License. You can obtain a copy
7		* in the file LICENSE in the source distribution or at
8		* https://www.openssl.org/source/license.html
9		*/
10
11		/*
12		* ECDSA low-level APIs are deprecated for public use, but still ok for
13		* internal use.
14		*/
15		#include "internal/deprecated.h"
16
17		#include <openssl/err.h>
18
19		#include "ec_local.h"
20
21		const EC_METHOD *EC_GFp_mont_method(void)
22	159k	{
23	159k	static const EC_METHOD ret = {
24	159k	EC_FLAGS_DEFAULT_OCT,
25	159k	NID_X9_62_prime_field,
26	159k	ossl_ec_GFp_mont_group_init,
27	159k	ossl_ec_GFp_mont_group_finish,
28	159k	ossl_ec_GFp_mont_group_clear_finish,
29	159k	ossl_ec_GFp_mont_group_copy,
30	159k	ossl_ec_GFp_mont_group_set_curve,
31	159k	ossl_ec_GFp_simple_group_get_curve,
32	159k	ossl_ec_GFp_simple_group_get_degree,
33	159k	ossl_ec_group_simple_order_bits,
34	159k	ossl_ec_GFp_simple_group_check_discriminant,
35	159k	ossl_ec_GFp_simple_point_init,
36	159k	ossl_ec_GFp_simple_point_finish,
37	159k	ossl_ec_GFp_simple_point_clear_finish,
38	159k	ossl_ec_GFp_simple_point_copy,
39	159k	ossl_ec_GFp_simple_point_set_to_infinity,
40	159k	ossl_ec_GFp_simple_point_set_affine_coordinates,
41	159k	ossl_ec_GFp_simple_point_get_affine_coordinates,
42	159k	0, 0, 0,
43	159k	ossl_ec_GFp_simple_add,
44	159k	ossl_ec_GFp_simple_dbl,
45	159k	ossl_ec_GFp_simple_invert,
46	159k	ossl_ec_GFp_simple_is_at_infinity,
47	159k	ossl_ec_GFp_simple_is_on_curve,
48	159k	ossl_ec_GFp_simple_cmp,
49	159k	ossl_ec_GFp_simple_make_affine,
50	159k	ossl_ec_GFp_simple_points_make_affine,
51	159k	0 /* mul */,
52	159k	0 /* precompute_mult */,
53	159k	0 /* have_precompute_mult */,
54	159k	ossl_ec_GFp_mont_field_mul,
55	159k	ossl_ec_GFp_mont_field_sqr,
56	159k	0 /* field_div */,
57	159k	ossl_ec_GFp_mont_field_inv,
58	159k	ossl_ec_GFp_mont_field_encode,
59	159k	ossl_ec_GFp_mont_field_decode,
60	159k	ossl_ec_GFp_mont_field_set_to_one,
61	159k	ossl_ec_key_simple_priv2oct,
62	159k	ossl_ec_key_simple_oct2priv,
63	159k	0, /* set private */
64	159k	ossl_ec_key_simple_generate_key,
65	159k	ossl_ec_key_simple_check_key,
66	159k	ossl_ec_key_simple_generate_public_key,
67	159k	0, /* keycopy */
68	159k	0, /* keyfinish */
69	159k	ossl_ecdh_simple_compute_key,
70	159k	ossl_ecdsa_simple_sign_setup,
71	159k	ossl_ecdsa_simple_sign_sig,
72	159k	ossl_ecdsa_simple_verify_sig,
73	159k	0, /* field_inverse_mod_ord */
74	159k	ossl_ec_GFp_simple_blind_coordinates,
75	159k	ossl_ec_GFp_simple_ladder_pre,
76	159k	ossl_ec_GFp_simple_ladder_step,
77	159k	ossl_ec_GFp_simple_ladder_post
78	159k	};
79
80	159k	return &ret;
81	159k	}
82
83		int ossl_ec_GFp_mont_group_init(EC_GROUP *group)
84	690k	{
85	690k	int ok;
86
87	690k	ok = ossl_ec_GFp_simple_group_init(group);
88	690k	group->field_data1 = NULL;
89	690k	group->field_data2 = NULL;
90	690k	return ok;
91	690k	}
92
93		void ossl_ec_GFp_mont_group_finish(EC_GROUP *group)
94	690k	{
95	690k	BN_MONT_CTX_free(group->field_data1);
96	690k	group->field_data1 = NULL;
97	690k	BN_free(group->field_data2);
98	690k	group->field_data2 = NULL;
99	690k	ossl_ec_GFp_simple_group_finish(group);
100	690k	}
101
102		void ossl_ec_GFp_mont_group_clear_finish(EC_GROUP *group)
103	0	{
104	0	BN_MONT_CTX_free(group->field_data1);
105	0	group->field_data1 = NULL;
106	0	BN_clear_free(group->field_data2);
107	0	group->field_data2 = NULL;
108	0	ossl_ec_GFp_simple_group_clear_finish(group);
109	0	}
110
111		int ossl_ec_GFp_mont_group_copy(EC_GROUP dest, const EC_GROUP src)
112	314k	{
113	314k	BN_MONT_CTX_free(dest->field_data1);
114	314k	dest->field_data1 = NULL;
115	314k	BN_clear_free(dest->field_data2);
116	314k	dest->field_data2 = NULL;
117
118	314k	if (!ossl_ec_GFp_simple_group_copy(dest, src))
119	0	return 0;
120
121	314k	if (src->field_data1 != NULL) {
122	314k	dest->field_data1 = BN_MONT_CTX_new();
123	314k	if (dest->field_data1 == NULL)
124	0	return 0;
125	314k	if (!BN_MONT_CTX_copy(dest->field_data1, src->field_data1))
126	0	goto err;
127	314k	}
128	314k	if (src->field_data2 != NULL) {
129	314k	dest->field_data2 = BN_dup(src->field_data2);
130	314k	if (dest->field_data2 == NULL)
131	0	goto err;
132	314k	}
133
134	314k	return 1;
135
136	0	err:
137	0	BN_MONT_CTX_free(dest->field_data1);
138	0	dest->field_data1 = NULL;
139	0	return 0;
140	314k	}
141
142		int ossl_ec_GFp_mont_group_set_curve(EC_GROUP group, const BIGNUM p,
143		const BIGNUM a, const BIGNUM b,
144		BN_CTX *ctx)
145	223k	{
146	223k	BN_CTX *new_ctx = NULL;
147	223k	BN_MONT_CTX *mont = NULL;
148	223k	BIGNUM *one = NULL;
149	223k	int ret = 0;
150
151	223k	BN_MONT_CTX_free(group->field_data1);
152	223k	group->field_data1 = NULL;
153	223k	BN_free(group->field_data2);
154	223k	group->field_data2 = NULL;
155
156	223k	if (ctx == NULL) {
157	22.4k	ctx = new_ctx = BN_CTX_new_ex(group->libctx);
158	22.4k	if (ctx == NULL)
159	0	return 0;
160	22.4k	}
161
162	223k	mont = BN_MONT_CTX_new();
163	223k	if (mont == NULL)
164	0	goto err;
165	223k	if (!BN_MONT_CTX_set(mont, p, ctx)) {
166	3.40k	ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
167	3.40k	goto err;
168	3.40k	}
169	219k	one = BN_new();
170	219k	if (one == NULL)
171	0	goto err;
172	219k	if (!BN_to_montgomery(one, BN_value_one(), mont, ctx))
173	0	goto err;
174
175	219k	group->field_data1 = mont;
176	219k	mont = NULL;
177	219k	group->field_data2 = one;
178	219k	one = NULL;
179
180	219k	ret = ossl_ec_GFp_simple_group_set_curve(group, p, a, b, ctx);
181
182	219k	if (!ret) {
183	50	BN_MONT_CTX_free(group->field_data1);
184	50	group->field_data1 = NULL;
185	50	BN_free(group->field_data2);
186	50	group->field_data2 = NULL;
187	50	}
188
189	223k	err:
190	223k	BN_free(one);
191	223k	BN_CTX_free(new_ctx);
192	223k	BN_MONT_CTX_free(mont);
193	223k	return ret;
194	219k	}
195
196		int ossl_ec_GFp_mont_field_mul(const EC_GROUP group, BIGNUM r, const BIGNUM *a,
197		const BIGNUM b, BN_CTX ctx)
198	38.9M	{
199	38.9M	if (group->field_data1 == NULL) {
200	0	ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
201	0	return 0;
202	0	}
203
204	38.9M	return BN_mod_mul_montgomery(r, a, b, group->field_data1, ctx);
205	38.9M	}
206
207		int ossl_ec_GFp_mont_field_sqr(const EC_GROUP group, BIGNUM r, const BIGNUM *a,
208		BN_CTX *ctx)
209	24.0M	{
210	24.0M	if (group->field_data1 == NULL) {
211	0	ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
212	0	return 0;
213	0	}
214
215	24.0M	return BN_mod_mul_montgomery(r, a, a, group->field_data1, ctx);
216	24.0M	}
217
218		/*-
219		* Computes the multiplicative inverse of a in GF(p), storing the result in r.
220		* If a is zero (or equivalent), you'll get an EC_R_CANNOT_INVERT error.
221		* We have a Mont structure, so SCA hardening is FLT inversion.
222		*/
223		int ossl_ec_GFp_mont_field_inv(const EC_GROUP group, BIGNUM r, const BIGNUM *a,
224		BN_CTX *ctx)
225	10.5k	{
226	10.5k	BIGNUM *e = NULL;
227	10.5k	BN_CTX *new_ctx = NULL;
228	10.5k	int ret = 0;
229
230	10.5k	if (group->field_data1 == NULL)
231	0	return 0;
232
233	10.5k	if (ctx == NULL
234	0	&& (ctx = new_ctx = BN_CTX_secure_new_ex(group->libctx)) == NULL)
235	0	return 0;
236
237	10.5k	BN_CTX_start(ctx);
238	10.5k	if ((e = BN_CTX_get(ctx)) == NULL)
239	0	goto err;
240
241		/* Inverse in constant time with Fermats Little Theorem */
242	10.5k	if (!BN_set_word(e, 2))
243	0	goto err;
244	10.5k	if (!BN_sub(e, group->field, e))
245	0	goto err;
246		/*-
247		* Exponent e is public.
248		* No need for scatter-gather or BN_FLG_CONSTTIME.
249		*/
250	10.5k	if (!BN_mod_exp_mont(r, a, e, group->field, ctx, group->field_data1))
251	0	goto err;
252
253		/* throw an error on zero */
254	10.5k	if (BN_is_zero(r)) {
255	0	ERR_raise(ERR_LIB_EC, EC_R_CANNOT_INVERT);
256	0	goto err;
257	0	}
258
259	10.5k	ret = 1;
260
261	10.5k	err:
262	10.5k	BN_CTX_end(ctx);
263	10.5k	BN_CTX_free(new_ctx);
264	10.5k	return ret;
265	10.5k	}
266
267		int ossl_ec_GFp_mont_field_encode(const EC_GROUP group, BIGNUM r,
268		const BIGNUM a, BN_CTX ctx)
269	2.03M	{
270	2.03M	if (group->field_data1 == NULL) {
271	0	ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
272	0	return 0;
273	0	}
274
275	2.03M	return BN_to_montgomery(r, a, (BN_MONT_CTX *)group->field_data1, ctx);
276	2.03M	}
277
278		int ossl_ec_GFp_mont_field_decode(const EC_GROUP group, BIGNUM r,
279		const BIGNUM a, BN_CTX ctx)
280	734k	{
281	734k	if (group->field_data1 == NULL) {
282	0	ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
283	0	return 0;
284	0	}
285
286	734k	return BN_from_montgomery(r, a, group->field_data1, ctx);
287	734k	}
288
289		int ossl_ec_GFp_mont_field_set_to_one(const EC_GROUP group, BIGNUM r,
290		BN_CTX *ctx)
291	578k	{
292	578k	if (group->field_data2 == NULL) {
293	0	ERR_raise(ERR_LIB_EC, EC_R_NOT_INITIALIZED);
294	0	return 0;
295	0	}
296
297	578k	if (!BN_copy(r, group->field_data2))
298	0	return 0;
299	578k	return 1;
300	578k	}