dh_gen.c

/* crypto/dh/dh_gen.c */ /* 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 "cryptlib.h" #include <openssl/bn.h> #include <openssl/dh.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); t1 = BN_CTX_get(ctx); t2 = BN_CTX_get(ctx); if (t1 == NULL || t2 == 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) { DHerr(DH_F_DH_BUILTIN_GENPARAMS, 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; } #if 0 /* does not work for safe primes */ else if (generator == DH_GENERATOR_3) { if (!BN_set_word(t1,12)) goto err; if (!BN_set_word(t2,5)) goto err; g=3; } #endif 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) { DHerr(DH_F_DH_BUILTIN_GENPARAMS,ERR_R_BN_LIB); ok=0; } if (ctx != NULL) { BN_CTX_end(ctx); BN_CTX_free(ctx); } return ok; }

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