--- /dev/null
+/*-
+ * 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;
+}
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