text: /* $OpenBSD: rsa_gen.c,v 1.16 2014/07/11 08:44:49 jsing Exp $ */
  /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   * All rights reserved.
   *
   * This package is an SSL implementation written
   * by Eric Young (eay@cryptsoft.com).
   * The implementation was written so as to conform with Netscapes SSL.
   *
   * This library is free for commercial and non-commercial use as long as
   * the following conditions are aheared to.  The following conditions
   * apply to all code found in this distribution, be it the RC4, RSA,
   * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
   * included with this distribution is covered by the same copyright terms
   * except that the holder is Tim Hudson (tjh@cryptsoft.com).
   *
   * Copyright remains Eric Young's, and as such any Copyright notices in
   * the code are not to be removed.
   * If this package is used in a product, Eric Young should be given attribution
   * as the author of the parts of the library used.
   * This can be in the form of a textual message at program startup or
   * in documentation (online or textual) provided with the package.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *    "This product includes cryptographic software written by
   *     Eric Young (eay@cryptsoft.com)"
   *    The word 'cryptographic' can be left out if the rouines from the library
   *    being used are not cryptographic related :-).
   * 4. If you include any Windows specific code (or a derivative thereof) from
   *    the apps directory (application code) you must include an acknowledgement:
   *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
   *
   * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * The licence and distribution terms for any publically available version or
   * derivative of this code cannot be changed.  i.e. this code cannot simply be
   * copied and put under another distribution licence
   * [including the GNU Public Licence.]
   */
  
  
  /* NB: these functions have been "upgraded", the deprecated versions (which are
   * compatibility wrappers using these functions) are in rsa_depr.c.
   * - Geoff
   */
  
  #include <stdio.h>
  #include <time.h>
  
  #include <openssl/bn.h>
  #include <openssl/err.h>
  #include <openssl/rsa.h>
  
  static int rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value, BN_GENCB *cb);
  
  /*
   * NB: this wrapper would normally be placed in rsa_lib.c and the static
   * implementation would probably be in rsa_eay.c. Nonetheless, is kept here so
   * that we don't introduce a new linker dependency. Eg. any application that
   * wasn't previously linking object code related to key-generation won't have to
   * now just because key-generation is part of RSA_METHOD.
   */
  int
  RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e_value, BN_GENCB *cb)
  {
  	if (rsa->meth->rsa_keygen)
  		return rsa->meth->rsa_keygen(rsa, bits, e_value, cb);
  	return rsa_builtin_keygen(rsa, bits, e_value, cb);
  }
  
  static int
  rsa_builtin_keygen(RSA *rsa, int bits, BIGNUM *e_value, BN_GENCB *cb)
  {
  	BIGNUM *r0 = NULL, *r1 = NULL, *r2 = NULL, *r3 = NULL, *tmp;
  	BIGNUM local_r0, local_d, local_p;
  	BIGNUM *pr0, *d, *p;
  	int bitsp, bitsq, ok = -1, n = 0;
  	BN_CTX *ctx = NULL;
  
  	ctx = BN_CTX_new();
  	if (ctx == NULL)
  		goto err;
  	BN_CTX_start(ctx);
  	if ((r0 = BN_CTX_get(ctx)) == NULL)
  		goto err;
  	if ((r1 = BN_CTX_get(ctx)) == NULL)
  		goto err;
  	if ((r2 = BN_CTX_get(ctx)) == NULL)
  		goto err;
  	if ((r3 = BN_CTX_get(ctx)) == NULL)
  		goto err;
  
  	bitsp = (bits + 1) / 2;
  	bitsq = bits - bitsp;
  
  	/* We need the RSA components non-NULL */
  	if (!rsa->n && ((rsa->n = BN_new()) == NULL))
  		goto err;
  	if (!rsa->d && ((rsa->d = BN_new()) == NULL))
  		goto err;
  	if (!rsa->e && ((rsa->e = BN_new()) == NULL))
  		goto err;
  	if (!rsa->p && ((rsa->p = BN_new()) == NULL))
  		goto err;
  	if (!rsa->q && ((rsa->q = BN_new()) == NULL))
  		goto err;
  	if (!rsa->dmp1 && ((rsa->dmp1 = BN_new()) == NULL))
  		goto err;
  	if (!rsa->dmq1 && ((rsa->dmq1 = BN_new()) == NULL))
  		goto err;
  	if (!rsa->iqmp && ((rsa->iqmp = BN_new()) == NULL))
  		goto err;
  
  	BN_copy(rsa->e, e_value);
  
  	/* generate p and q */
  	for (;;) {
  		if (!BN_generate_prime_ex(rsa->p, bitsp, 0, NULL, NULL, cb))
  			goto err;
  		if (!BN_sub(r2, rsa->p, BN_value_one()))
  			goto err;
  		if (!BN_gcd(r1, r2, rsa->e, ctx))
  			goto err;
  		if (BN_is_one(r1))
  			break;
  		if (!BN_GENCB_call(cb, 2, n++))
  			goto err;
  	}
  	if (!BN_GENCB_call(cb, 3, 0))
  		goto err;
  	for (;;) {
  		/*
  		 * When generating ridiculously small keys, we can get stuck
  		 * continually regenerating the same prime values. Check for
  		 * this and bail if it happens 3 times.
  		 */
  		unsigned int degenerate = 0;
  		do {
  			if (!BN_generate_prime_ex(rsa->q, bitsq, 0, NULL, NULL,
  			    cb))
  				goto err;
  		} while (BN_cmp(rsa->p, rsa->q) == 0 &&
  		    ++degenerate < 3);
  		if (degenerate == 3) {
  			ok = 0; /* we set our own err */
  			RSAerr(RSA_F_RSA_BUILTIN_KEYGEN,
  			    RSA_R_KEY_SIZE_TOO_SMALL);
  			goto err;
  		}
  		if (!BN_sub(r2, rsa->q, BN_value_one()))
  			goto err;
  		if (!BN_gcd(r1, r2, rsa->e, ctx))
  			goto err;
  		if (BN_is_one(r1))
  			break;
  		if (!BN_GENCB_call(cb, 2, n++))
  			goto err;
  	}
  	if (!BN_GENCB_call(cb, 3, 1))
  		goto err;
  	if (BN_cmp(rsa->p, rsa->q) < 0) {
  		tmp = rsa->p;
  		rsa->p = rsa->q;
  		rsa->q = tmp;
  	}
  
  	/* calculate n */
  	if (!BN_mul(rsa->n, rsa->p, rsa->q, ctx))
  		goto err;
  
  	/* calculate d */
  	if (!BN_sub(r1, rsa->p, BN_value_one()))	/* p-1 */
  		goto err;
  	if (!BN_sub(r2, rsa->q, BN_value_one()))	/* q-1 */
  		goto err;
  	if (!BN_mul(r0, r1, r2, ctx))			/* (p-1)(q-1) */
  		goto err;
  	if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME)) {
  		pr0 = &local_r0;
  		BN_with_flags(pr0, r0, BN_FLG_CONSTTIME);
  	} else
  		pr0 = r0;
  	if (!BN_mod_inverse(rsa->d, rsa->e, pr0, ctx))	/* d */
  		goto err;
  
  	/* set up d for correct BN_FLG_CONSTTIME flag */
  	if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME)) {
  		d = &local_d;
  		BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
  	} else
  		d = rsa->d;
  
  	/* calculate d mod (p-1) */
  	if (!BN_mod(rsa->dmp1, d, r1, ctx))
  		goto err;
  
  	/* calculate d mod (q-1) */
  	if (!BN_mod(rsa->dmq1, d, r2, ctx))
  		goto err;
  
  	/* calculate inverse of q mod p */
  	if (!(rsa->flags & RSA_FLAG_NO_CONSTTIME)) {
  		p = &local_p;
  		BN_with_flags(p, rsa->p, BN_FLG_CONSTTIME);
  	} else
  		p = rsa->p;
  	if (!BN_mod_inverse(rsa->iqmp, rsa->q, p, ctx))
  		goto err;
  
  	ok = 1;
  err:
  	if (ok == -1) {
  		RSAerr(RSA_F_RSA_BUILTIN_KEYGEN, ERR_LIB_BN);
  		ok = 0;
  	}
  	if (ctx != NULL) {
  		BN_CTX_end(ctx);
  		BN_CTX_free(ctx);
  	}
  
  	return ok;
  }
  