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/* $OpenBSD: dh_gen.c,v 1.16 2017/01/29 17:49:22 beck 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 previous prototypes are in
* dh_depr.c as wrappers to these ones.
* - Geoff
*/
#include <stdio.h>
#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/err.h>
static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
BN_GENCB *cb);
int
DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
{
if (ret->meth->generate_params)
return ret->meth->generate_params(ret, prime_len, generator, cb);
return dh_builtin_genparams(ret, prime_len, generator, cb);
}
/*
* We generate DH parameters as follows:
* find a prime q which is prime_len/2 bits long.
* p=(2*q)+1 or (p-1)/2 = q
* For this case, g is a generator if
* g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
* Since the factors of p-1 are q and 2, we just need to check
* g^2 mod p != 1 and g^q mod p != 1.
*
* Having said all that,
* there is another special case method for the generators 2, 3 and 5.
* for 2, p mod 24 == 11
* for 3, p mod 12 == 5 <<<<< does not work for safe primes.
* for 5, p mod 10 == 3 or 7
*
* Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
* special generators and for answering some of my questions.
*
* I've implemented the second simple method :-).
* Since DH should be using a safe prime (both p and q are prime),
* this generator function can take a very very long time to run.
*/
/* Actually there is no reason to insist that 'generator' be a generator.
* It's just as OK (and in some sense better) to use a generator of the
* order-q subgroup.
*/
static int
dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)
{
BIGNUM *t1, *t2;
int g, ok = -1;
BN_CTX *ctx = NULL;
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
BN_CTX_start(ctx);
if ((t1 = BN_CTX_get(ctx)) == NULL)
goto err;
if ((t2 = BN_CTX_get(ctx)) == NULL)
goto err;
/* Make sure 'ret' has the necessary elements */
if (!ret->p && ((ret->p = BN_new()) == NULL))
goto err;
if (!ret->g && ((ret->g = BN_new()) == NULL))
goto err;
if (generator <= 1) {
DHerror(DH_R_BAD_GENERATOR);
goto err;
}
if (generator == DH_GENERATOR_2) {
if (!BN_set_word(t1, 24))
goto err;
if (!BN_set_word(t2, 11))
goto err;
g = 2;
} else if (generator == DH_GENERATOR_5) {
if (!BN_set_word(t1, 10))
goto err;
if (!BN_set_word(t2, 3))
goto err;
/* BN_set_word(t3,7); just have to miss
* out on these ones :-( */
g = 5;
} else {
/*
* in the general case, don't worry if 'generator' is a
* generator or not: since we are using safe primes,
* it will generate either an order-q or an order-2q group,
* which both is OK
*/
if (!BN_set_word(t1, 2))
goto err;
if (!BN_set_word(t2, 1))
goto err;
g = generator;
}
if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
goto err;
if (!BN_GENCB_call(cb, 3, 0))
goto err;
if (!BN_set_word(ret->g, g))
goto err;
ok = 1;
err:
if (ok == -1) {
DHerror(ERR_R_BN_LIB);
ok = 0;
}
if (ctx != NULL) {
BN_CTX_end(ctx);
BN_CTX_free(ctx);
}
return ok;
}
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