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  */
19 int 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 1;
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     /* Step(1): Verify pub_key <=  p-2 */
45     if (BN_copy(tmp, params->p) == NULL
46         || !BN_sub_word(tmp, 1))
47         goto err;
48     if (BN_cmp(pub_key, tmp) >= 0)
49         *ret |= FFC_ERROR_PUBKEY_TOO_LARGE;
50     ok = 1;
51  err:
52     if (ctx != NULL) {
53         BN_CTX_end(ctx);
54         BN_CTX_free(ctx);
55     }
56     return ok;
57 }
58 
59 /*
60  * See SP800-56Ar3 Section 5.6.2.3.1 : FFC Full public key validation.
61  */
62 int ossl_ffc_validate_public_key(const FFC_PARAMS *params,
63                                  const BIGNUM *pub_key, int *ret)
64 {
65     int ok = 0;
66     BIGNUM *tmp = NULL;
67     BN_CTX *ctx = NULL;
68 
69     if (!ossl_ffc_validate_public_key_partial(params, pub_key, ret))
70         return 0;
71 
72     if (*ret == 0 && params->q != NULL) {
73         ctx = BN_CTX_new_ex(NULL);
74         if (ctx == NULL)
75             goto err;
76         BN_CTX_start(ctx);
77         tmp = BN_CTX_get(ctx);
78 
79         /* Check pub_key^q == 1 mod p */
80         if (tmp == NULL
81             || !BN_mod_exp(tmp, pub_key, params->q, params->p, ctx))
82             goto err;
83         if (!BN_is_one(tmp))
84             *ret |= FFC_ERROR_PUBKEY_INVALID;
85     }
86 
87     ok = 1;
88  err:
89     if (ctx != NULL) {
90         BN_CTX_end(ctx);
91         BN_CTX_free(ctx);
92     }
93     return ok;
94 }
95 
96 /*
97  * See SP800-56Ar3 Section 5.6.2.1.2: Owner assurance of Private key validity.
98  * Verifies priv_key is in the range [1..upper-1]. The passed in value of upper
99  * is normally params->q but can be 2^N for approved safe prime groups.
100  * Note: This assumes that the domain parameters are valid.
101  */
102 int ossl_ffc_validate_private_key(const BIGNUM *upper, const BIGNUM *priv,
103                                   int *ret)
104 {
105     int ok = 0;
106 
107     *ret = 0;
108 
109     if (priv == NULL || upper == NULL) {
110         *ret = FFC_ERROR_PASSED_NULL_PARAM;
111         goto err;
112     }
113     if (BN_cmp(priv, BN_value_one()) < 0) {
114         *ret |= FFC_ERROR_PRIVKEY_TOO_SMALL;
115         goto err;
116     }
117     if (BN_cmp(priv, upper) >= 0) {
118         *ret |= FFC_ERROR_PRIVKEY_TOO_LARGE;
119         goto err;
120     }
121     ok = 1;
122 err:
123     return ok;
124 }
125