Viewing file:  EVP_PKEY_RSA_keygen.c (8.92 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
/*-
* Copyright 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 RSA key pair.
*
* When generating an RSA key, you must specify the number of bits in the key. A
* reasonable value would be 4096. Avoid using values below 2048. These values
* are reasonable as of 2022.
*/
#include <string.h>
#include <stdio.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <openssl/core_names.h>
#include <openssl/pem.h>
/* A property query used for selecting algorithm implementations. */
static const char *propq = NULL;
/*
* Generates an RSA public-private key pair and returns it.
* The number of bits is specified by the bits argument.
*
* This uses the long way of generating an RSA key.
*/
static EVP_PKEY *generate_rsa_key_long(OSSL_LIB_CTX *libctx, unsigned int bits)
{
EVP_PKEY_CTX *genctx = NULL;
EVP_PKEY *pkey = NULL;
unsigned int primes = 2;
/* Create context using RSA algorithm. "RSA-PSS" could also be used here. */
genctx = EVP_PKEY_CTX_new_from_name(libctx, "RSA", propq);
if (genctx == NULL) {
fprintf(stderr, "EVP_PKEY_CTX_new_from_name() failed\n");
goto cleanup;
}
/* Initialize context for key generation purposes. */
if (EVP_PKEY_keygen_init(genctx) <= 0) {
fprintf(stderr, "EVP_PKEY_keygen_init() failed\n");
goto cleanup;
}
/*
* Here we set the number of bits to use in the RSA key.
* See comment at top of file for information on appropriate values.
*/
if (EVP_PKEY_CTX_set_rsa_keygen_bits(genctx, bits) <= 0) {
fprintf(stderr, "EVP_PKEY_CTX_set_rsa_keygen_bits() failed\n");
goto cleanup;
}
/*
* It is possible to create an RSA key using more than two primes.
* Do not do this unless you know why you need this.
* You ordinarily do not need to specify this, as the default is two.
*
* Both of these parameters can also be set via EVP_PKEY_CTX_set_params, but
* these functions provide a more concise way to do so.
*/
if (EVP_PKEY_CTX_set_rsa_keygen_primes(genctx, primes) <= 0) {
fprintf(stderr, "EVP_PKEY_CTX_set_rsa_keygen_primes() failed\n");
goto cleanup;
}
/*
* Generating an RSA key with a number of bits large enough to be secure for
* modern applications can take a fairly substantial amount of time (e.g.
* one second). If you require fast key generation, consider using an EC key
* instead.
*
* If you require progress information during the key generation process,
* you can set a progress callback using EVP_PKEY_set_cb; see the example in
* EVP_PKEY_generate(3).
*/
fprintf(stderr, "Generating RSA key, this may take some time...\n");
if (EVP_PKEY_generate(genctx, &pkey) <= 0) {
fprintf(stderr, "EVP_PKEY_generate() failed\n");
goto cleanup;
}
/* pkey is now set to an object representing the generated key pair. */
cleanup:
EVP_PKEY_CTX_free(genctx);
return pkey;
}
/*
* Generates an RSA public-private key pair and returns it.
* The number of bits is specified by the bits argument.
*
* This uses a more concise way of generating an RSA key, which is suitable for
* simple cases. It is used if -s is passed on the command line, otherwise the
* long method above is used. The ability to choose between these two methods is
* shown here only for demonstration; the results are equivalent.
*/
static EVP_PKEY *generate_rsa_key_short(OSSL_LIB_CTX *libctx, unsigned int bits)
{
EVP_PKEY *pkey = NULL;
fprintf(stderr, "Generating RSA key, this may take some time...\n");
pkey = EVP_PKEY_Q_keygen(libctx, propq, "RSA", (size_t)bits);
if (pkey == NULL)
fprintf(stderr, "EVP_PKEY_Q_keygen() failed\n");
return pkey;
}
/*
* Prints information on an EVP_PKEY object representing an RSA key pair.
*/
static int dump_key(const EVP_PKEY *pkey)
{
int rv = 0;
int bits = 0;
BIGNUM *n = NULL, *e = NULL, *d = NULL, *p = NULL, *q = NULL;
/*
* Retrieve value of n. This value is not secret and forms part of the
* public key.
*
* Calling EVP_PKEY_get_bn_param with a NULL BIGNUM pointer causes
* a new BIGNUM to be allocated, so these must be freed subsequently.
*/
if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_N, &n) == 0) {
fprintf(stderr, "Failed to retrieve n\n");
goto cleanup;
}
/*
* Retrieve value of e. This value is not secret and forms part of the
* public key. It is typically 65537 and need not be changed.
*/
if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_E, &e) == 0) {
fprintf(stderr, "Failed to retrieve e\n");
goto cleanup;
}
/*
* Retrieve value of d. This value is secret and forms part of the private
* key. It must not be published.
*/
if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_D, &d) == 0) {
fprintf(stderr, "Failed to retrieve d\n");
goto cleanup;
}
/*
* Retrieve value of the first prime factor, commonly known as p. This value
* is secret and forms part of the private key. It must not be published.
*/
if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_FACTOR1, &p) == 0) {
fprintf(stderr, "Failed to retrieve p\n");
goto cleanup;
}
/*
* Retrieve value of the second prime factor, commonly known as q. This value
* is secret and forms part of the private key. It must not be published.
*
* If you are creating an RSA key with more than two primes for special
* applications, you can retrieve these primes with
* OSSL_PKEY_PARAM_RSA_FACTOR3, etc.
*/
if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_FACTOR2, &q) == 0) {
fprintf(stderr, "Failed to retrieve q\n");
goto cleanup;
}
/*
* We can also retrieve the key size in bits for informational purposes.
*/
if (EVP_PKEY_get_int_param(pkey, OSSL_PKEY_PARAM_BITS, &bits) == 0) {
fprintf(stderr, "Failed to retrieve bits\n");
goto cleanup;
}
/* Output hexadecimal representations of the BIGNUM objects. */
fprintf(stdout, "\nNumber of bits: %d\n\n", bits);
fprintf(stderr, "Public values:\n");
fprintf(stdout, " n = 0x");
BN_print_fp(stdout, n);
fprintf(stdout, "\n");
fprintf(stdout, " e = 0x");
BN_print_fp(stdout, e);
fprintf(stdout, "\n\n");
fprintf(stdout, "Private values:\n");
fprintf(stdout, " d = 0x");
BN_print_fp(stdout, d);
fprintf(stdout, "\n");
fprintf(stdout, " p = 0x");
BN_print_fp(stdout, p);
fprintf(stdout, "\n");
fprintf(stdout, " q = 0x");
BN_print_fp(stdout, q);
fprintf(stdout, "\n\n");
/* Output a PEM encoding of the public key. */
if (PEM_write_PUBKEY(stdout, pkey) == 0) {
fprintf(stderr, "Failed to output PEM-encoded public key\n");
goto cleanup;
}
/*
* Output a PEM encoding of the private key. Please note that this output is
* not encrypted. You may wish to use the arguments to specify encryption of
* the key if you are storing it on disk. See PEM_write_PrivateKey(3).
*/
if (PEM_write_PrivateKey(stdout, pkey, NULL, NULL, 0, NULL, NULL) == 0) {
fprintf(stderr, "Failed to output PEM-encoded private key\n");
goto cleanup;
}
rv = 1;
cleanup:
BN_free(n); /* not secret */
BN_free(e); /* not secret */
BN_clear_free(d); /* secret - scrub before freeing */
BN_clear_free(p); /* secret - scrub before freeing */
BN_clear_free(q); /* secret - scrub before freeing */
return rv;
}
int main(int argc, char **argv)
{
int rv = 1;
OSSL_LIB_CTX *libctx = NULL;
EVP_PKEY *pkey = NULL;
unsigned int bits = 4096;
int bits_i, use_short = 0;
/* usage: [-s] [<bits>] */
if (argc > 1 && strcmp(argv[1], "-s") == 0) {
--argc;
++argv;
use_short = 1;
}
if (argc > 1) {
bits_i = atoi(argv[1]);
if (bits < 512) {
fprintf(stderr, "Invalid RSA key size\n");
return 1;
}
bits = (unsigned int)bits_i;
}
/* Avoid using key sizes less than 2048 bits; see comment at top of file. */
if (bits < 2048)
fprintf(stderr, "Warning: very weak key size\n\n");
/* Generate RSA key. */
if (use_short)
pkey = generate_rsa_key_short(libctx, bits);
else
pkey = generate_rsa_key_long(libctx, bits);
if (pkey == NULL)
goto cleanup;
/* Dump the integers comprising the key. */
if (dump_key(pkey) == 0) {
fprintf(stderr, "Failed to dump key\n");
goto cleanup;
}
rv = 0;
cleanup:
EVP_PKEY_free(pkey);
OSSL_LIB_CTX_free(libctx);
return rv;
}
|