demos/pkey/EVP_PKEY_EC_keygen.c

   1 /*-
   2  * Copyright 2021 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  */
  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  */
  85 static 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 i, 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;
 126 cleanup:
 127     /* Zeroize the private key data when we free it */
 128     BN_clear_free(out_priv);
 129     return result;
 130 }
 131
 132 int 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;
 149 cleanup:
 150     if (result != 1)
 151         ERR_print_errors_fp(stderr);
 152
 153     EVP_PKEY_free(pkey);
 154     return result == 0;
 155 }