1/*-
2 * Copyright 2021-2022 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
21static 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 */
30static 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    }
74cleanup:
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 */
85static int get_key_values(EVP_PKEY *pkey)
86{
87    int result = 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    result = 1;
126cleanup:
127    /* Zeroize the private key data when we free it */
128    BN_clear_free(out_priv);
129    return result;
130}
131
132int main(void)
133{
134    int result = 0;
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    result = 1;
149cleanup:
150    if (result != 1)
151        ERR_print_errors_fp(stderr);
152
153    EVP_PKEY_free(pkey);
154    return result == 0;
155}
156