/* $OpenBSD: dh_check.c,v 1.29 2024/08/30 17:44:56 tb 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.] */ #include #include #include #include #include "bn_local.h" #include "dh_local.h" #define DH_NUMBER_ITERATIONS_FOR_PRIME 64 /* * Check that p is odd and 1 < g < p - 1. */ static int DH_check_params(const DH *dh, int *flags) { BIGNUM *max_g = NULL; int ok = 0; *flags = 0; if (!BN_is_odd(dh->p)) *flags |= DH_CHECK_P_NOT_PRIME; /* * Check that 1 < dh->g < p - 1 */ if (BN_cmp(dh->g, BN_value_one()) <= 0) *flags |= DH_NOT_SUITABLE_GENERATOR; /* max_g = p - 1 */ if ((max_g = BN_dup(dh->p)) == NULL) goto err; if (!BN_sub_word(max_g, 1)) goto err; /* check that g < max_g */ if (BN_cmp(dh->g, max_g) >= 0) *flags |= DH_NOT_SUITABLE_GENERATOR; ok = 1; err: BN_free(max_g); return ok; } /* * Check that p is a safe prime and that g is a suitable generator. */ int DH_check(const DH *dh, int *flags) { BN_CTX *ctx = NULL; int is_prime; int ok = 0; *flags = 0; if (!DH_check_params(dh, flags)) goto err; ctx = BN_CTX_new(); if (ctx == NULL) goto err; BN_CTX_start(ctx); if (dh->q != NULL) { BIGNUM *quotient, *residue; if ((quotient = BN_CTX_get(ctx)) == NULL) goto err; if ((residue = BN_CTX_get(ctx)) == NULL) goto err; if ((*flags & DH_NOT_SUITABLE_GENERATOR) == 0) { /* Check g^q == 1 mod p */ if (!BN_mod_exp_ct(residue, dh->g, dh->q, dh->p, ctx)) goto err; if (!BN_is_one(residue)) *flags |= DH_NOT_SUITABLE_GENERATOR; } is_prime = BN_is_prime_ex(dh->q, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL); if (is_prime < 0) goto err; if (is_prime == 0) *flags |= DH_CHECK_Q_NOT_PRIME; /* Check p == 1 mod q, i.e., q divides p - 1 */ if (!BN_div_ct(quotient, residue, dh->p, dh->q, ctx)) goto err; if (!BN_is_one(residue)) *flags |= DH_CHECK_INVALID_Q_VALUE; if (dh->j != NULL && BN_cmp(dh->j, quotient) != 0) *flags |= DH_CHECK_INVALID_J_VALUE; } is_prime = BN_is_prime_ex(dh->p, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL); if (is_prime < 0) goto err; if (is_prime == 0) *flags |= DH_CHECK_P_NOT_PRIME; else if (dh->q == NULL) { BIGNUM *q; if ((q = BN_CTX_get(ctx)) == NULL) goto err; if (!BN_rshift1(q, dh->p)) goto err; is_prime = BN_is_prime_ex(q, DH_NUMBER_ITERATIONS_FOR_PRIME, ctx, NULL); if (is_prime < 0) goto err; if (is_prime == 0) *flags |= DH_CHECK_P_NOT_SAFE_PRIME; } ok = 1; err: BN_CTX_end(ctx); BN_CTX_free(ctx); return ok; } LCRYPTO_ALIAS(DH_check); int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *flags) { BN_CTX *ctx = NULL; BIGNUM *max_pub_key; int ok = 0; *flags = 0; if ((ctx = BN_CTX_new()) == NULL) goto err; BN_CTX_start(ctx); if ((max_pub_key = BN_CTX_get(ctx)) == NULL) goto err; /* * Check that 1 < pub_key < dh->p - 1 */ if (BN_cmp(pub_key, BN_value_one()) <= 0) *flags |= DH_CHECK_PUBKEY_TOO_SMALL; /* max_pub_key = dh->p - 1 */ if (!BN_sub(max_pub_key, dh->p, BN_value_one())) goto err; if (BN_cmp(pub_key, max_pub_key) >= 0) *flags |= DH_CHECK_PUBKEY_TOO_LARGE; /* * If dh->q is set, check that pub_key^q == 1 mod p */ if (dh->q != NULL) { BIGNUM *residue; if ((residue = BN_CTX_get(ctx)) == NULL) goto err; if (!BN_mod_exp_ct(residue, pub_key, dh->q, dh->p, ctx)) goto err; if (!BN_is_one(residue)) *flags |= DH_CHECK_PUBKEY_INVALID; } ok = 1; err: BN_CTX_end(ctx); BN_CTX_free(ctx); return ok; } LCRYPTO_ALIAS(DH_check_pub_key);