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/*-
* Copyright 2021-2022 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
/*
* Example showing how to generate an EC key and extract values from the
* generated key.
*/
#include <string.h>
#include <stdio.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/core_names.h>
static int get_key_values(EVP_PKEY *pkey);
/*
* The following code shows how to generate an EC key from a curve name
* with additional parameters. If only the curve name is required then the
* simple helper can be used instead i.e. Either
* pkey = EVP_EC_gen(curvename); OR
* pkey = EVP_PKEY_Q_keygen(libctx, propq, "EC", curvename);
*/
static EVP_PKEY *do_ec_keygen(void)
{
/*
* The libctx and propq can be set if required, they are included here
* to show how they are passed to EVP_PKEY_CTX_new_from_name().
*/
OSSL_LIB_CTX *libctx = NULL;
const char *propq = NULL;
EVP_PKEY *key = NULL;
OSSL_PARAM params[3];
EVP_PKEY_CTX *genctx = NULL;
const char *curvename = "P-256";
int use_cofactordh = 1;
genctx = EVP_PKEY_CTX_new_from_name(libctx, "EC", propq);
if (genctx == NULL) {
fprintf(stderr, "EVP_PKEY_CTX_new_from_name() failed\n");
goto cleanup;
}
if (EVP_PKEY_keygen_init(genctx) <= 0) {
fprintf(stderr, "EVP_PKEY_keygen_init() failed\n");
goto cleanup;
}
params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME,
(char *)curvename, 0);
/*
* This is an optional parameter.
* For many curves where the cofactor is 1, setting this has no effect.
*/
params[1] = OSSL_PARAM_construct_int(OSSL_PKEY_PARAM_USE_COFACTOR_ECDH,
&use_cofactordh);
params[2] = OSSL_PARAM_construct_end();
if (!EVP_PKEY_CTX_set_params(genctx, params)) {
fprintf(stderr, "EVP_PKEY_CTX_set_params() failed\n");
goto cleanup;
}
fprintf(stdout, "Generating EC key\n\n");
if (EVP_PKEY_generate(genctx, &key) <= 0) {
fprintf(stderr, "EVP_PKEY_generate() failed\n");
goto cleanup;
}
cleanup:
EVP_PKEY_CTX_free(genctx);
return key;
}
/*
* The following code shows how retrieve key data from the generated
* EC key. See doc/man7/EVP_PKEY-EC.pod for more information.
*
* EVP_PKEY_print_private() could also be used to display the values.
*/
static int get_key_values(EVP_PKEY *pkey)
{
int result = 0;
char out_curvename[80];
unsigned char out_pubkey[80];
unsigned char out_privkey[80];
BIGNUM *out_priv = NULL;
size_t out_pubkey_len, out_privkey_len = 0;
if (!EVP_PKEY_get_utf8_string_param(pkey, OSSL_PKEY_PARAM_GROUP_NAME,
out_curvename, sizeof(out_curvename),
NULL)) {
fprintf(stderr, "Failed to get curve name\n");
goto cleanup;
}
if (!EVP_PKEY_get_octet_string_param(pkey, OSSL_PKEY_PARAM_PUB_KEY,
out_pubkey, sizeof(out_pubkey),
&out_pubkey_len)) {
fprintf(stderr, "Failed to get public key\n");
goto cleanup;
}
if (!EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_PRIV_KEY, &out_priv)) {
fprintf(stderr, "Failed to get private key\n");
goto cleanup;
}
out_privkey_len = BN_bn2bin(out_priv, out_privkey);
if (out_privkey_len <= 0 || out_privkey_len > sizeof(out_privkey)) {
fprintf(stderr, "BN_bn2bin failed\n");
goto cleanup;
}
fprintf(stdout, "Curve name: %s\n", out_curvename);
fprintf(stdout, "Public key:\n");
BIO_dump_indent_fp(stdout, out_pubkey, out_pubkey_len, 2);
fprintf(stdout, "Private Key:\n");
BIO_dump_indent_fp(stdout, out_privkey, out_privkey_len, 2);
result = 1;
cleanup:
/* Zeroize the private key data when we free it */
BN_clear_free(out_priv);
return result;
}
int main(void)
{
int result = 0;
EVP_PKEY *pkey;
pkey = do_ec_keygen();
if (pkey == NULL)
goto cleanup;
if (!get_key_values(pkey))
goto cleanup;
/*
* At this point we can write out the generated key using
* i2d_PrivateKey() and i2d_PublicKey() if required.
*/
result = 1;
cleanup:
if (result != 1)
ERR_print_errors_fp(stderr);
EVP_PKEY_free(pkey);
return result == 0;
}
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