180 lines
6.2 KiB
C
180 lines
6.2 KiB
C
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/* $OpenBSD: dh_gen.c,v 1.16 2017/01/29 17:49:22 beck Exp $ */
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/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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* All rights reserved.
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*
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* This package is an SSL implementation written
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* by Eric Young (eay@cryptsoft.com).
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* The implementation was written so as to conform with Netscapes SSL.
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*
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* This library is free for commercial and non-commercial use as long as
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* the following conditions are aheared to. The following conditions
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* apply to all code found in this distribution, be it the RC4, RSA,
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* lhash, DES, etc., code; not just the SSL code. The SSL documentation
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* included with this distribution is covered by the same copyright terms
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* except that the holder is Tim Hudson (tjh@cryptsoft.com).
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*
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* Copyright remains Eric Young's, and as such any Copyright notices in
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* the code are not to be removed.
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* If this package is used in a product, Eric Young should be given attribution
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* as the author of the parts of the library used.
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* This can be in the form of a textual message at program startup or
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* in documentation (online or textual) provided with the package.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* "This product includes cryptographic software written by
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* Eric Young (eay@cryptsoft.com)"
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* The word 'cryptographic' can be left out if the rouines from the library
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* being used are not cryptographic related :-).
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* 4. If you include any Windows specific code (or a derivative thereof) from
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* the apps directory (application code) you must include an acknowledgement:
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* "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
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*
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* THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* The licence and distribution terms for any publically available version or
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* derivative of this code cannot be changed. i.e. this code cannot simply be
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* copied and put under another distribution licence
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* [including the GNU Public Licence.]
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*/
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/* NB: These functions have been upgraded - the previous prototypes are in
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* dh_depr.c as wrappers to these ones.
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* - Geoff
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*/
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#include <stdio.h>
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#include <openssl/bn.h>
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#include <openssl/dh.h>
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#include <openssl/err.h>
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static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
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BN_GENCB *cb);
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int
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DH_generate_parameters_ex(DH *ret, int prime_len, int generator, BN_GENCB *cb)
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{
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if (ret->meth->generate_params)
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return ret->meth->generate_params(ret, prime_len, generator, cb);
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return dh_builtin_genparams(ret, prime_len, generator, cb);
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}
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/*
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* We generate DH parameters as follows:
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* find a prime q which is prime_len/2 bits long.
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* p=(2*q)+1 or (p-1)/2 = q
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* For this case, g is a generator if
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* g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
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* Since the factors of p-1 are q and 2, we just need to check
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* g^2 mod p != 1 and g^q mod p != 1.
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*
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* Having said all that,
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* there is another special case method for the generators 2, 3 and 5.
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* for 2, p mod 24 == 11
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* for 3, p mod 12 == 5 <<<<< does not work for safe primes.
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* for 5, p mod 10 == 3 or 7
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*
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* Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
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* special generators and for answering some of my questions.
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*
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* I've implemented the second simple method :-).
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* Since DH should be using a safe prime (both p and q are prime),
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* this generator function can take a very very long time to run.
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*/
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/* Actually there is no reason to insist that 'generator' be a generator.
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* It's just as OK (and in some sense better) to use a generator of the
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* order-q subgroup.
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*/
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static int
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dh_builtin_genparams(DH *ret, int prime_len, int generator, BN_GENCB *cb)
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{
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BIGNUM *t1, *t2;
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int g, ok = -1;
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BN_CTX *ctx = NULL;
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ctx = BN_CTX_new();
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if (ctx == NULL)
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goto err;
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BN_CTX_start(ctx);
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if ((t1 = BN_CTX_get(ctx)) == NULL)
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goto err;
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if ((t2 = BN_CTX_get(ctx)) == NULL)
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goto err;
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/* Make sure 'ret' has the necessary elements */
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if (!ret->p && ((ret->p = BN_new()) == NULL))
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goto err;
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if (!ret->g && ((ret->g = BN_new()) == NULL))
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goto err;
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if (generator <= 1) {
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DHerror(DH_R_BAD_GENERATOR);
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goto err;
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}
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if (generator == DH_GENERATOR_2) {
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if (!BN_set_word(t1, 24))
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goto err;
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if (!BN_set_word(t2, 11))
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goto err;
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g = 2;
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} else if (generator == DH_GENERATOR_5) {
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if (!BN_set_word(t1, 10))
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goto err;
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if (!BN_set_word(t2, 3))
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goto err;
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/* BN_set_word(t3,7); just have to miss
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* out on these ones :-( */
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g = 5;
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} else {
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/*
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* in the general case, don't worry if 'generator' is a
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* generator or not: since we are using safe primes,
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* it will generate either an order-q or an order-2q group,
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* which both is OK
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*/
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if (!BN_set_word(t1, 2))
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goto err;
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if (!BN_set_word(t2, 1))
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goto err;
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g = generator;
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}
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if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
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goto err;
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if (!BN_GENCB_call(cb, 3, 0))
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goto err;
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if (!BN_set_word(ret->g, g))
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goto err;
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ok = 1;
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err:
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if (ok == -1) {
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DHerror(ERR_R_BN_LIB);
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ok = 0;
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}
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if (ctx != NULL) {
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BN_CTX_end(ctx);
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BN_CTX_free(ctx);
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}
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return ok;
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}
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