demos/pkey/EVP_PKEY_RSA_keygen.c

   1 /*-
   2  * Copyright 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 RSA key pair.
  12  *
  13  * When generating an RSA key, you must specify the number of bits in the key. A
  14  * reasonable value would be 4096. Avoid using values below 2048. These values
  15  * are reasonable as of 2022.
  16  */
  17
  18 #include <string.h>
  19 #include <stdio.h>
  20 #include <openssl/err.h>
  21 #include <openssl/evp.h>
  22 #include <openssl/rsa.h>
  23 #include <openssl/core_names.h>
  24 #include <openssl/pem.h>
  25
  26 /* A property query used for selecting algorithm implementations. */
  27 static const char *propq = NULL;
  28
  29 /*
  30  * Generates an RSA public-private key pair and returns it.
  31  * The number of bits is specified by the bits argument.
  32  *
  33  * This uses the long way of generating an RSA key.
  34  */
  35 static EVP_PKEY *generate_rsa_key_long(OSSL_LIB_CTX *libctx, unsigned int bits)
  36 {
  37     EVP_PKEY_CTX *genctx = NULL;
  38     EVP_PKEY *pkey = NULL;
  39     unsigned int primes = 2;
  40
  41     /* Create context using RSA algorithm. "RSA-PSS" could also be used here. */
  42     genctx = EVP_PKEY_CTX_new_from_name(libctx, "RSA", propq);
  43     if (genctx == NULL) {
  44         fprintf(stderr, "EVP_PKEY_CTX_new_from_name() failed\n");
  45         goto cleanup;
  46     }
  47
  48     /* Initialize context for key generation purposes. */
  49     if (EVP_PKEY_keygen_init(genctx) <= 0) {
  50         fprintf(stderr, "EVP_PKEY_keygen_init() failed\n");
  51         goto cleanup;
  52     }
  53
  54     /*
  55      * Here we set the number of bits to use in the RSA key.
  56      * See comment at top of file for information on appropriate values.
  57      */
  58     if (EVP_PKEY_CTX_set_rsa_keygen_bits(genctx, bits) <= 0) {
  59         fprintf(stderr, "EVP_PKEY_CTX_set_rsa_keygen_bits() failed\n");
  60         goto cleanup;
  61     }
  62
  63     /*
  64      * It is possible to create an RSA key using more than two primes.
  65      * Do not do this unless you know why you need this.
  66      * You ordinarily do not need to specify this, as the default is two.
  67      *
  68      * Both of these parameters can also be set via EVP_PKEY_CTX_set_params, but
  69      * these functions provide a more concise way to do so.
  70      */
  71     if (EVP_PKEY_CTX_set_rsa_keygen_primes(genctx, primes) <= 0) {
  72         fprintf(stderr, "EVP_PKEY_CTX_set_rsa_keygen_primes() failed\n");
  73         goto cleanup;
  74     }
  75
  76     /*
  77      * Generating an RSA key with a number of bits large enough to be secure for
  78      * modern applications can take a fairly substantial amount of time (e.g.
  79      * one second). If you require fast key generation, consider using an EC key
  80      * instead.
  81      *
  82      * If you require progress information during the key generation process,
  83      * you can set a progress callback using EVP_PKEY_set_cb; see the example in
  84      * EVP_PKEY_generate(3).
  85      */
  86     fprintf(stderr, "Generating RSA key, this may take some time...\n");
  87     if (EVP_PKEY_generate(genctx, &pkey) <= 0) {
  88         fprintf(stderr, "EVP_PKEY_generate() failed\n");
  89         goto cleanup;
  90     }
  91
  92     /* pkey is now set to an object representing the generated key pair. */
  93
  94 cleanup:
  95     EVP_PKEY_CTX_free(genctx);
  96     return pkey;
  97 }
  98
  99 /*
 100  * Generates an RSA public-private key pair and returns it.
 101  * The number of bits is specified by the bits argument.
 102  *
 103  * This uses a more concise way of generating an RSA key, which is suitable for
 104  * simple cases. It is used if -s is passed on the command line, otherwise the
 105  * long method above is used. The ability to choose between these two methods is
 106  * shown here only for demonstration; the results are equivalent.
 107  */
 108 static EVP_PKEY *generate_rsa_key_short(OSSL_LIB_CTX *libctx, unsigned int bits)
 109 {
 110     EVP_PKEY *pkey = NULL;
 111
 112     fprintf(stderr, "Generating RSA key, this may take some time...\n");
 113     pkey = EVP_PKEY_Q_keygen(libctx, propq, "RSA", (size_t)bits);
 114
 115     if (pkey == NULL)
 116         fprintf(stderr, "EVP_PKEY_Q_keygen() failed\n");
 117
 118     return pkey;
 119 }
 120
 121 /*
 122  * Prints information on an EVP_PKEY object representing an RSA key pair.
 123  */
 124 static int dump_key(const EVP_PKEY *pkey)
 125 {
 126     int rv = 0;
 127     int bits = 0;
 128     BIGNUM *n = NULL, *e = NULL, *d = NULL, *p = NULL, *q = NULL;
 129
 130     /*
 131      * Retrieve value of n. This value is not secret and forms part of the
 132      * public key.
 133      *
 134      * Calling EVP_PKEY_get_bn_param with a NULL BIGNUM pointer causes
 135      * a new BIGNUM to be allocated, so these must be freed subsequently.
 136      */
 137     if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_N, &n) == 0) {
 138         fprintf(stderr, "Failed to retrieve n\n");
 139         goto cleanup;
 140     }
 141
 142     /*
 143      * Retrieve value of e. This value is not secret and forms part of the
 144      * public key. It is typically 65537 and need not be changed.
 145      */
 146     if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_E, &e) == 0) {
 147         fprintf(stderr, "Failed to retrieve e\n");
 148         goto cleanup;
 149     }
 150
 151     /*
 152      * Retrieve value of d. This value is secret and forms part of the private
 153      * key. It must not be published.
 154      */
 155     if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_D, &d) == 0) {
 156         fprintf(stderr, "Failed to retrieve d\n");
 157         goto cleanup;
 158     }
 159
 160     /*
 161      * Retrieve value of the first prime factor, commonly known as p. This value
 162      * is secret and forms part of the private key. It must not be published.
 163      */
 164     if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_FACTOR1, &p) == 0) {
 165         fprintf(stderr, "Failed to retrieve p\n");
 166         goto cleanup;
 167     }
 168
 169     /*
 170      * Retrieve value of the second prime factor, commonly known as q. This value
 171      * is secret and forms part of the private key. It must not be published.
 172      *
 173      * If you are creating an RSA key with more than two primes for special
 174      * applications, you can retrieve these primes with
 175      * OSSL_PKEY_PARAM_RSA_FACTOR3, etc.
 176      */
 177     if (EVP_PKEY_get_bn_param(pkey, OSSL_PKEY_PARAM_RSA_FACTOR2, &q) == 0) {
 178         fprintf(stderr, "Failed to retrieve q\n");
 179         goto cleanup;
 180     }
 181
 182     /*
 183      * We can also retrieve the key size in bits for informational purposes.
 184      */
 185     if (EVP_PKEY_get_int_param(pkey, OSSL_PKEY_PARAM_BITS, &bits) == 0) {
 186         fprintf(stderr, "Failed to retrieve bits\n");
 187         goto cleanup;
 188     }
 189
 190     /* Output hexadecimal representations of the BIGNUM objects. */
 191     fprintf(stdout, "\nNumber of bits: %d\n\n", bits);
 192     fprintf(stderr, "Public values:\n");
 193     fprintf(stdout, "  n = 0x");
 194     BN_print_fp(stdout, n);
 195     fprintf(stdout, "\n");
 196
 197     fprintf(stdout, "  e = 0x");
 198     BN_print_fp(stdout, e);
 199     fprintf(stdout, "\n\n");
 200
 201     fprintf(stdout, "Private values:\n");
 202     fprintf(stdout, "  d = 0x");
 203     BN_print_fp(stdout, d);
 204     fprintf(stdout, "\n");
 205
 206     fprintf(stdout, "  p = 0x");
 207     BN_print_fp(stdout, p);
 208     fprintf(stdout, "\n");
 209
 210     fprintf(stdout, "  q = 0x");
 211     BN_print_fp(stdout, q);
 212     fprintf(stdout, "\n\n");
 213
 214     /* Output a PEM encoding of the public key. */
 215     if (PEM_write_PUBKEY(stdout, pkey) == 0) {
 216         fprintf(stderr, "Failed to output PEM-encoded public key\n");
 217         goto cleanup;
 218     }
 219
 220     /*
 221      * Output a PEM encoding of the private key. Please note that this output is
 222      * not encrypted. You may wish to use the arguments to specify encryption of
 223      * the key if you are storing it on disk. See PEM_write_PrivateKey(3).
 224      */
 225     if (PEM_write_PrivateKey(stdout, pkey, NULL, NULL, 0, NULL, NULL) == 0) {
 226         fprintf(stderr, "Failed to output PEM-encoded private key\n");
 227         goto cleanup;
 228     }
 229
 230     rv = 1;
 231 cleanup:
 232     BN_free(n); /* not secret */
 233     BN_free(e); /* not secret */
 234     BN_clear_free(d); /* secret - scrub before freeing */
 235     BN_clear_free(p); /* secret - scrub before freeing */
 236     BN_clear_free(q); /* secret - scrub before freeing */
 237     return rv;
 238 }
 239
 240 int main(int argc, char **argv)
 241 {
 242     int rv = 1;
 243     OSSL_LIB_CTX *libctx = NULL;
 244     EVP_PKEY *pkey = NULL;
 245     unsigned int bits = 4096;
 246     int bits_i, use_short = 0;
 247
 248     /* usage: [-s] [<bits>] */
 249     if (argc > 1 && strcmp(argv[1], "-s") == 0) {
 250         --argc;
 251         ++argv;
 252         use_short = 1;
 253     }
 254
 255     if (argc > 1) {
 256         bits_i = atoi(argv[1]);
 257         if (bits < 512) {
 258             fprintf(stderr, "Invalid RSA key size\n");
 259             return 1;
 260         }
 261
 262         bits = (unsigned int)bits_i;
 263     }
 264
 265     /* Avoid using key sizes less than 2048 bits; see comment at top of file. */
 266     if (bits < 2048)
 267         fprintf(stderr, "Warning: very weak key size\n\n");
 268
 269     /* Generate RSA key. */
 270     if (use_short)
 271         pkey = generate_rsa_key_short(libctx, bits);
 272     else
 273         pkey = generate_rsa_key_long(libctx, bits);
 274
 275     if (pkey == NULL)
 276         goto cleanup;
 277
 278     /* Dump the integers comprising the key. */
 279     if (dump_key(pkey) == 0) {
 280         fprintf(stderr, "Failed to dump key\n");
 281         goto cleanup;
 282     }
 283
 284     rv = 0;
 285 cleanup:
 286     EVP_PKEY_free(pkey);
 287     OSSL_LIB_CTX_free(libctx);
 288     return rv;
 289 }