1/*
2 * Copyright 2019-2023 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/ffc.h"
11
12/*
13 * See SP800-56Ar3 Section 5.6.2.3.1 : FFC Partial public key validation.
14 * To only be used with ephemeral FFC public keys generated using the approved
15 * safe-prime groups. (Checks that the public key is in the range [2, p - 1]
16 *
17 * ret contains 0 on success, or error flags (see FFC_ERROR_PUBKEY_TOO_SMALL)
18 */
19int ossl_ffc_validate_public_key_partial(const FFC_PARAMS *params,
20                                         const BIGNUM *pub_key, int *ret)
21{
22    int ok = 0;
23    BIGNUM *tmp = NULL;
24    BN_CTX *ctx = NULL;
25
26    *ret = 0;
27    if (params == NULL || pub_key == NULL || params->p == NULL) {
28        *ret = FFC_ERROR_PASSED_NULL_PARAM;
29        return 0;
30    }
31
32    ctx = BN_CTX_new_ex(NULL);
33    if (ctx == NULL)
34        goto err;
35
36    BN_CTX_start(ctx);
37    tmp = BN_CTX_get(ctx);
38    /* Step(1): Verify pub_key >= 2 */
39    if (tmp == NULL
40        || !BN_set_word(tmp, 1))
41        goto err;
42    if (BN_cmp(pub_key, tmp) <= 0) {
43        *ret |= FFC_ERROR_PUBKEY_TOO_SMALL;
44        goto err;
45    }
46    /* Step(1): Verify pub_key <=  p-2 */
47    if (BN_copy(tmp, params->p) == NULL
48        || !BN_sub_word(tmp, 1))
49        goto err;
50    if (BN_cmp(pub_key, tmp) >= 0) {
51        *ret |= FFC_ERROR_PUBKEY_TOO_LARGE;
52        goto err;
53    }
54    ok = 1;
55 err:
56    if (ctx != NULL) {
57        BN_CTX_end(ctx);
58        BN_CTX_free(ctx);
59    }
60    return ok;
61}
62
63/*
64 * See SP800-56Ar3 Section 5.6.2.3.1 : FFC Full public key validation.
65 */
66int ossl_ffc_validate_public_key(const FFC_PARAMS *params,
67                                 const BIGNUM *pub_key, int *ret)
68{
69    int ok = 0;
70    BIGNUM *tmp = NULL;
71    BN_CTX *ctx = NULL;
72
73    if (!ossl_ffc_validate_public_key_partial(params, pub_key, ret))
74        return 0;
75
76    if (params->q != NULL) {
77        ctx = BN_CTX_new_ex(NULL);
78        if (ctx == NULL)
79            goto err;
80        BN_CTX_start(ctx);
81        tmp = BN_CTX_get(ctx);
82
83        /* Check pub_key^q == 1 mod p */
84        if (tmp == NULL
85            || !BN_mod_exp(tmp, pub_key, params->q, params->p, ctx))
86            goto err;
87        if (!BN_is_one(tmp)) {
88            *ret |= FFC_ERROR_PUBKEY_INVALID;
89            goto err;
90        }
91    }
92
93    ok = 1;
94 err:
95    if (ctx != NULL) {
96        BN_CTX_end(ctx);
97        BN_CTX_free(ctx);
98    }
99    return ok;
100}
101
102/*
103 * See SP800-56Ar3 Section 5.6.2.1.2: Owner assurance of Private key validity.
104 * Verifies priv_key is in the range [1..upper-1]. The passed in value of upper
105 * is normally params->q but can be 2^N for approved safe prime groups.
106 * Note: This assumes that the domain parameters are valid.
107 */
108int ossl_ffc_validate_private_key(const BIGNUM *upper, const BIGNUM *priv,
109                                  int *ret)
110{
111    int ok = 0;
112
113    *ret = 0;
114
115    if (priv == NULL || upper == NULL) {
116        *ret = FFC_ERROR_PASSED_NULL_PARAM;
117        goto err;
118    }
119    if (BN_cmp(priv, BN_value_one()) < 0) {
120        *ret |= FFC_ERROR_PRIVKEY_TOO_SMALL;
121        goto err;
122    }
123    if (BN_cmp(priv, upper) >= 0) {
124        *ret |= FFC_ERROR_PRIVKEY_TOO_LARGE;
125        goto err;
126    }
127    ok = 1;
128err:
129    return ok;
130}
131