1 /*-
2 * Copyright 2021-2023 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 /*
11 * Example showing how to generate an EC key and extract values from the
12 * generated key.
13 */
14
15 #include <string.h>
16 #include <stdio.h>
17 #include <openssl/err.h>
18 #include <openssl/evp.h>
19 #include <openssl/core_names.h>
20
21 static int get_key_values(EVP_PKEY *pkey);
22
23 /*
24 * The following code shows how to generate an EC key from a curve name
25 * with additional parameters. If only the curve name is required then the
26 * simple helper can be used instead i.e. Either
27 * pkey = EVP_EC_gen(curvename); OR
28 * pkey = EVP_PKEY_Q_keygen(libctx, propq, "EC", curvename);
29 */
do_ec_keygen(void)30 static EVP_PKEY *do_ec_keygen(void)
31 {
32 /*
33 * The libctx and propq can be set if required, they are included here
34 * to show how they are passed to EVP_PKEY_CTX_new_from_name().
35 */
36 OSSL_LIB_CTX *libctx = NULL;
37 const char *propq = NULL;
38 EVP_PKEY *key = NULL;
39 OSSL_PARAM params[3];
40 EVP_PKEY_CTX *genctx = NULL;
41 const char *curvename = "P-256";
42 int use_cofactordh = 1;
43
44 genctx = EVP_PKEY_CTX_new_from_name(libctx, "EC", propq);
45 if (genctx == NULL) {
46 fprintf(stderr, "EVP_PKEY_CTX_new_from_name() failed\n");
47 goto cleanup;
48 }
49
50 if (EVP_PKEY_keygen_init(genctx) <= 0) {
51 fprintf(stderr, "EVP_PKEY_keygen_init() failed\n");
52 goto cleanup;
53 }
54
55 params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
56 (char *)curvename, 0);
57 /*
58 * This is an optional parameter.
59 * For many curves where the cofactor is 1, setting this has no effect.
60 */
61 params[1] = OSSL_PARAM_construct_int(OSSL_PKEY_PARAM_USE_COFACTOR_ECDH,
62 &use_cofactordh);
63 params[2] = OSSL_PARAM_construct_end();
64 if (!EVP_PKEY_CTX_set_params(genctx, params)) {
65 fprintf(stderr, "EVP_PKEY_CTX_set_params() failed\n");
66 goto cleanup;
67 }
68
69 fprintf(stdout, "Generating EC key\n\n");
70 if (EVP_PKEY_generate(genctx, &key) <= 0) {
71 fprintf(stderr, "EVP_PKEY_generate() failed\n");
72 goto cleanup;
73 }
74 cleanup:
75 EVP_PKEY_CTX_free(genctx);
76 return key;
77 }
78
79 /*
80 * The following code shows how retrieve key data from the generated
81 * EC key. See doc/man7/EVP_PKEY-EC.pod for more information.
82 *
83 * EVP_PKEY_print_private() could also be used to display the values.
84 */
get_key_values(EVP_PKEY * pkey)85 static int get_key_values(EVP_PKEY *pkey)
86 {
87 int ret = 0;
88 char out_curvename[80];
89 unsigned char out_pubkey[80];
90 unsigned char out_privkey[80];
91 BIGNUM *out_priv = NULL;
92 size_t out_pubkey_len, out_privkey_len = 0;
93
94 if (!EVP_PKEY_get_utf8_string_param(pkey, OSSL_PKEY_PARAM_GROUP_NAME,
95 out_curvename, sizeof(out_curvename),
96 NULL)) {
97 fprintf(stderr, "Failed to get curve name\n");
98 goto cleanup;
99 }
100
101 if (!EVP_PKEY_get_octet_string_param(pkey, OSSL_PKEY_PARAM_PUB_KEY,
102 out_pubkey, sizeof(out_pubkey),
103 &out_pubkey_len)) {
104 fprintf(stderr, "Failed to get public key\n");
105 goto cleanup;
106 }
107
108 if (!EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_PRIV_KEY, &out_priv)) {
109 fprintf(stderr, "Failed to get private key\n");
110 goto cleanup;
111 }
112
113 out_privkey_len = BN_bn2bin(out_priv, out_privkey);
114 if (out_privkey_len <= 0 || out_privkey_len > sizeof(out_privkey)) {
115 fprintf(stderr, "BN_bn2bin failed\n");
116 goto cleanup;
117 }
118
119 fprintf(stdout, "Curve name: %s\n", out_curvename);
120 fprintf(stdout, "Public key:\n");
121 BIO_dump_indent_fp(stdout, out_pubkey, out_pubkey_len, 2);
122 fprintf(stdout, "Private Key:\n");
123 BIO_dump_indent_fp(stdout, out_privkey, out_privkey_len, 2);
124
125 ret = 1;
126 cleanup:
127 /* Zeroize the private key data when we free it */
128 BN_clear_free(out_priv);
129 return ret;
130 }
131
main(void)132 int main(void)
133 {
134 int ret = EXIT_FAILURE;
135 EVP_PKEY *pkey;
136
137 pkey = do_ec_keygen();
138 if (pkey == NULL)
139 goto cleanup;
140
141 if (!get_key_values(pkey))
142 goto cleanup;
143
144 /*
145 * At this point we can write out the generated key using
146 * i2d_PrivateKey() and i2d_PublicKey() if required.
147 */
148 ret = EXIT_SUCCESS;
149 cleanup:
150 if (ret != EXIT_SUCCESS)
151 ERR_print_errors_fp(stderr);
152
153 EVP_PKEY_free(pkey);
154 return ret;
155 }
156
