dh.c - security/openssh-library - Rivoreo Source Code Repositories

 /* $OpenBSD: dh.c,v 1.58 2016/02/28 22:27:00 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  *
  * 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 above 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.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
  */

 #include "includes.h"

 #include <sys/param.h>	/* MIN */

 #include <openssl/bn.h>
 #include <openssl/dh.h>

 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <limits.h>

 #include "dh.h"
 #include "pathnames.h"
 #include "log.h"
 #include "misc.h"
 #include "ssherr.h"

 static int
 parse_prime(int linenum, char *line, struct dhgroup *dhg)
 {
 	char *cp, *arg;
 	char *strsize, *gen, *prime;
 	const char *errstr = NULL;
 	long long n;

 	dhg->p = dhg->g = NULL;
 	cp = line;
 	if ((arg = strdelim(&cp)) == NULL)
 		return 0;
 	/* Ignore leading whitespace */
 	if (*arg == '\0')
 		arg = strdelim(&cp);
 	if (!arg || !*arg || *arg == '#')
 		return 0;

 	/* time */
 	if (cp == NULL || *arg == '\0')
 		goto truncated;
 	arg = strsep(&cp, " "); /* type */
 	if (cp == NULL || *arg == '\0')
 		goto truncated;
 	/* Ensure this is a safe prime */
 	n = strtonum(arg, 0, 5, &errstr);
 	if (errstr != NULL || n != MODULI_TYPE_SAFE) {
 		error("moduli:%d: type is not %d", linenum, MODULI_TYPE_SAFE);
 		goto fail;
 	}
 	arg = strsep(&cp, " "); /* tests */
 	if (cp == NULL || *arg == '\0')
 		goto truncated;
 	/* Ensure prime has been tested and is not composite */
 	n = strtonum(arg, 0, 0x1f, &errstr);
 	if (errstr != NULL ||
 	    (n & MODULI_TESTS_COMPOSITE) || !(n & ~MODULI_TESTS_COMPOSITE)) {
 		error("moduli:%d: invalid moduli tests flag", linenum);
 		goto fail;
 	}
 	arg = strsep(&cp, " "); /* tries */
 	if (cp == NULL || *arg == '\0')
 		goto truncated;
 	n = strtonum(arg, 0, 1<<30, &errstr);
 	if (errstr != NULL || n == 0) {
 		error("moduli:%d: invalid primality trial count", linenum);
 		goto fail;
 	}
 	strsize = strsep(&cp, " "); /* size */
 	if (cp == NULL || *strsize == '\0' ||
 	    (dhg->size = (int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 ||
 	    errstr) {
 		error("moduli:%d: invalid prime length", linenum);
 		goto fail;
 	}
 	/* The whole group is one bit larger */
 	dhg->size++;
 	gen = strsep(&cp, " "); /* gen */
 	if (cp == NULL || *gen == '\0')
 		goto truncated;
 	prime = strsep(&cp, " "); /* prime */
 	if (cp != NULL || *prime == '\0') {
  truncated:
 		error("moduli:%d: truncated", linenum);
 		goto fail;
 	}

 	if ((dhg->g = BN_new()) == NULL ||
 	    (dhg->p = BN_new()) == NULL) {
 		error("parse_prime: BN_new failed");
 		goto fail;
 	}
 	if (BN_hex2bn(&dhg->g, gen) == 0) {
 		error("moduli:%d: could not parse generator value", linenum);
 		goto fail;
 	}
 	if (BN_hex2bn(&dhg->p, prime) == 0) {
 		error("moduli:%d: could not parse prime value", linenum);
 		goto fail;
 	}
 	if (BN_num_bits(dhg->p) != dhg->size) {
 		error("moduli:%d: prime has wrong size: actual %d listed %d",
 		    linenum, BN_num_bits(dhg->p), dhg->size - 1);
 		goto fail;
 	}
 	if (BN_cmp(dhg->g, BN_value_one()) <= 0) {
 		error("moduli:%d: generator is invalid", linenum);
 		goto fail;
 	}
 	return 1;

  fail:
 	if (dhg->g != NULL)
 		BN_clear_free(dhg->g);
 	if (dhg->p != NULL)
 		BN_clear_free(dhg->p);
 	dhg->g = dhg->p = NULL;
 	return 0;
 }

 DH *
 choose_dh(int min, int wantbits, int max)
 {
 	FILE *f;
 	char line[4096];
 	int best, bestcount, which;
 	int linenum;
 	struct dhgroup dhg;

 	if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL &&
 	    (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) {
 		logit("WARNING: %s does not exist, using fixed modulus",
 		    _PATH_DH_MODULI);
 		return (dh_new_group_fallback(max));
 	}

 	linenum = 0;
 	best = bestcount = 0;
 	while (fgets(line, sizeof(line), f)) {
 		linenum++;
 		if (!parse_prime(linenum, line, &dhg))
 			continue;
 		BN_clear_free(dhg.g);
 		BN_clear_free(dhg.p);

 		if (dhg.size > max || dhg.size < min)
 			continue;

 		if ((dhg.size > wantbits && dhg.size < best) ||
 		    (dhg.size > best && best < wantbits)) {
 			best = dhg.size;
 			bestcount = 0;
 		}
 		if (dhg.size == best)
 			bestcount++;
 	}
 	rewind(f);

 	if (bestcount == 0) {
 		fclose(f);
 		logit("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
 		return (dh_new_group_fallback(max));
 	}

 	linenum = 0;
 	which = arc4random_uniform(bestcount);
 	while (fgets(line, sizeof(line), f)) {
 		if (!parse_prime(linenum, line, &dhg))
 			continue;
 		if ((dhg.size > max || dhg.size < min) ||
 		    dhg.size != best ||
 		    linenum++ != which) {
 			BN_clear_free(dhg.g);
 			BN_clear_free(dhg.p);
 			continue;
 		}
 		break;
 	}
 	fclose(f);
 	if (linenum != which+1) {
 		logit("WARNING: line %d disappeared in %s, giving up",
 		    which, _PATH_DH_PRIMES);
 		return (dh_new_group_fallback(max));
 	}

 	return (dh_new_group(dhg.g, dhg.p));
 }

 /* diffie-hellman-groupN-sha1 */

 int
 dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
 {
 	int i;
 	int n = BN_num_bits(dh_pub);
 	int bits_set = 0;
 	BIGNUM *tmp;

 	if (dh_pub->neg) {
 		logit("invalid public DH value: negative");
 		return 0;
 	}
 	if (BN_cmp(dh_pub, BN_value_one()) != 1) {	/* pub_exp <= 1 */
 		logit("invalid public DH value: <= 1");
 		return 0;
 	}

 	if ((tmp = BN_new()) == NULL) {
 		error("%s: BN_new failed", __func__);
 		return 0;
 	}
 	if (!BN_sub(tmp, dh->p, BN_value_one()) ||
 	    BN_cmp(dh_pub, tmp) != -1) {		/* pub_exp > p-2 */
 		BN_clear_free(tmp);
 		logit("invalid public DH value: >= p-1");
 		return 0;
 	}
 	BN_clear_free(tmp);

 	for (i = 0; i <= n; i++)
 		if (BN_is_bit_set(dh_pub, i))
 			bits_set++;
 	debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p));

 	/*
 	 * if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial
 	 */
 	if (bits_set < 4) {
 		logit("invalid public DH value (%d/%d)",
 		   bits_set, BN_num_bits(dh->p));
 		return 0;
 	}
 	return 1;
 }

 int
 dh_gen_key(DH *dh, int need)
 {
 	int pbits;

 	if (need < 0 || dh->p == NULL ||
 	    (pbits = BN_num_bits(dh->p)) <= 0 ||
 	    need > INT_MAX / 2 || 2 * need > pbits)
 		return SSH_ERR_INVALID_ARGUMENT;
 	if (need < 256)
 		need = 256;
 	/*
 	 * Pollard Rho, Big step/Little Step attacks are O(sqrt(n)),
 	 * so double requested need here.
 	 */
 	dh->length = MIN(need * 2, pbits - 1);
 	if (DH_generate_key(dh) == 0 ||
 	    !dh_pub_is_valid(dh, dh->pub_key)) {
 		BN_clear_free(dh->priv_key);
 		return SSH_ERR_LIBCRYPTO_ERROR;
 	}
 	return 0;
 }

 DH *
 dh_new_group_asc(const char *gen, const char *modulus)
 {
 	DH *dh;

 	if ((dh = DH_new()) == NULL)
 		return NULL;
 	if (BN_hex2bn(&dh->p, modulus) == 0 ||
 	    BN_hex2bn(&dh->g, gen) == 0) {
 		DH_free(dh);
 		return NULL;
 	}
 	return (dh);
 }

 /*
  * This just returns the group, we still need to generate the exchange
  * value.
  */

 DH *
 dh_new_group(BIGNUM *gen, BIGNUM *modulus)
 {
 	DH *dh;

 	if ((dh = DH_new()) == NULL)
 		return NULL;
 	dh->p = modulus;
 	dh->g = gen;

 	return (dh);
 }

 DH *
 dh_new_group1(void)
 {
 	static char *gen = "2", *group1 =
 	    "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
 	    "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
 	    "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
 	    "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
 	    "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
 	    "FFFFFFFF" "FFFFFFFF";

 	return (dh_new_group_asc(gen, group1));
 }

 DH *
 dh_new_group14(void)
 {
 	static char *gen = "2", *group14 =
 	    "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
 	    "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
 	    "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
 	    "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
 	    "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"
 	    "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"
 	    "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"
 	    "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"
 	    "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"
 	    "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"
 	    "15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF";

 	return (dh_new_group_asc(gen, group14));
 }

 /*
  * 4k bit fallback group used by DH-GEX if moduli file cannot be read.
  * Source: MODP group 16 from RFC3526.
  */
 DH *
 dh_new_group_fallback(int max)
 {
 	static char *gen = "2", *group16 =
 	    "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
 	    "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
 	    "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
 	    "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
 	    "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"
 	    "C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"
 	    "83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"
 	    "670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"
 	    "E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"
 	    "DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"
 	    "15728E5A" "8AAAC42D" "AD33170D" "04507A33" "A85521AB" "DF1CBA64"
 	    "ECFB8504" "58DBEF0A" "8AEA7157" "5D060C7D" "B3970F85" "A6E1E4C7"
 	    "ABF5AE8C" "DB0933D7" "1E8C94E0" "4A25619D" "CEE3D226" "1AD2EE6B"
 	    "F12FFA06" "D98A0864" "D8760273" "3EC86A64" "521F2B18" "177B200C"
 	    "BBE11757" "7A615D6C" "770988C0" "BAD946E2" "08E24FA0" "74E5AB31"
 	    "43DB5BFC" "E0FD108E" "4B82D120" "A9210801" "1A723C12" "A787E6D7"
 	    "88719A10" "BDBA5B26" "99C32718" "6AF4E23C" "1A946834" "B6150BDA"
 	    "2583E9CA" "2AD44CE8" "DBBBC2DB" "04DE8EF9" "2E8EFC14" "1FBECAA6"
 	    "287C5947" "4E6BC05D" "99B2964F" "A090C3A2" "233BA186" "515BE7ED"
 	    "1F612970" "CEE2D7AF" "B81BDD76" "2170481C" "D0069127" "D5B05AA9"
 	    "93B4EA98" "8D8FDDC1" "86FFB7DC" "90A6C08F" "4DF435C9" "34063199"
 	    "FFFFFFFF" "FFFFFFFF";

 	if (max < 4096) {
 		debug3("requested max size %d, using 2k bit group 14", max);
 		return dh_new_group14();
 	}
 	debug3("using 4k bit group 16");
 	return (dh_new_group_asc(gen, group16));
 }

 /*
  * Estimates the group order for a Diffie-Hellman group that has an
  * attack complexity approximately the same as O(2**bits).
  * Values from NIST Special Publication 800-57: Recommendation for Key
  * Management Part 1 (rev 3) limited by the recommended maximum value
  * from RFC4419 section 3.
  */

 u_int
 dh_estimate(int bits)
 {
 	if (bits <= 112)
 		return 2048;
 	if (bits <= 128)
 		return 3072;
 	if (bits <= 192)
 		return 7680;
 	return 8192;
 }
	/* $OpenBSD: dh.c,v 1.58 2016/02/28 22:27:00 djm Exp $ */
	/*
	* Copyright (c) 2000 Niels Provos. All rights reserved.
	*
	* 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 above 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.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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.
	*/

	#include "includes.h"

	#include <sys/param.h> /* MIN */

	#include <openssl/bn.h>
	#include <openssl/dh.h>

	#include <stdarg.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <limits.h>

	#include "dh.h"
	#include "pathnames.h"
	#include "log.h"
	#include "misc.h"
	#include "ssherr.h"

	static int
	parse_prime(int linenum, char line, struct dhgroup dhg)
	{
	char cp, arg;
	char strsize, gen, *prime;
	const char *errstr = NULL;
	long long n;

	dhg->p = dhg->g = NULL;
	cp = line;
	if ((arg = strdelim(&cp)) == NULL)
	return 0;
	/* Ignore leading whitespace */
	if (*arg == '\0')
	arg = strdelim(&cp);
	if (!arg \|\| !arg \|\| arg == '#')
	return 0;

	/* time */
	if (cp == NULL \|\| *arg == '\0')
	goto truncated;
	arg = strsep(&cp, " "); /* type */
	if (cp == NULL \|\| *arg == '\0')
	goto truncated;
	/* Ensure this is a safe prime */
	n = strtonum(arg, 0, 5, &errstr);
	if (errstr != NULL \|\| n != MODULI_TYPE_SAFE) {
	error("moduli:%d: type is not %d", linenum, MODULI_TYPE_SAFE);
	goto fail;
	}
	arg = strsep(&cp, " "); /* tests */
	if (cp == NULL \|\| *arg == '\0')
	goto truncated;
	/* Ensure prime has been tested and is not composite */
	n = strtonum(arg, 0, 0x1f, &errstr);
	if (errstr != NULL \|\|
	(n & MODULI_TESTS_COMPOSITE) \|\| !(n & ~MODULI_TESTS_COMPOSITE)) {
	error("moduli:%d: invalid moduli tests flag", linenum);
	goto fail;
	}
	arg = strsep(&cp, " "); /* tries */
	if (cp == NULL \|\| *arg == '\0')
	goto truncated;
	n = strtonum(arg, 0, 1<<30, &errstr);
	if (errstr != NULL \|\| n == 0) {
	error("moduli:%d: invalid primality trial count", linenum);
	goto fail;
	}
	strsize = strsep(&cp, " "); /* size */
	if (cp == NULL \|\| *strsize == '\0' \|\|
	(dhg->size = (int)strtonum(strsize, 0, 64*1024, &errstr)) == 0 \|\|
	errstr) {
	error("moduli:%d: invalid prime length", linenum);
	goto fail;
	}
	/* The whole group is one bit larger */
	dhg->size++;
	gen = strsep(&cp, " "); /* gen */
	if (cp == NULL \|\| *gen == '\0')
	goto truncated;
	prime = strsep(&cp, " "); /* prime */
	if (cp != NULL \|\| *prime == '\0') {
	truncated:
	error("moduli:%d: truncated", linenum);
	goto fail;
	}

	if ((dhg->g = BN_new()) == NULL \|\|
	(dhg->p = BN_new()) == NULL) {
	error("parse_prime: BN_new failed");
	goto fail;
	}
	if (BN_hex2bn(&dhg->g, gen) == 0) {
	error("moduli:%d: could not parse generator value", linenum);
	goto fail;
	}
	if (BN_hex2bn(&dhg->p, prime) == 0) {
	error("moduli:%d: could not parse prime value", linenum);
	goto fail;
	}
	if (BN_num_bits(dhg->p) != dhg->size) {
	error("moduli:%d: prime has wrong size: actual %d listed %d",
	linenum, BN_num_bits(dhg->p), dhg->size - 1);
	goto fail;
	}
	if (BN_cmp(dhg->g, BN_value_one()) <= 0) {
	error("moduli:%d: generator is invalid", linenum);
	goto fail;
	}
	return 1;

	fail:
	if (dhg->g != NULL)
	BN_clear_free(dhg->g);
	if (dhg->p != NULL)
	BN_clear_free(dhg->p);
	dhg->g = dhg->p = NULL;
	return 0;
	}

	DH *
	choose_dh(int min, int wantbits, int max)
	{
	FILE *f;
	char line[4096];
	int best, bestcount, which;
	int linenum;
	struct dhgroup dhg;

	if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL &&
	(f = fopen(_PATH_DH_PRIMES, "r")) == NULL) {
	logit("WARNING: %s does not exist, using fixed modulus",
	_PATH_DH_MODULI);
	return (dh_new_group_fallback(max));
	}

	linenum = 0;
	best = bestcount = 0;
	while (fgets(line, sizeof(line), f)) {
	linenum++;
	if (!parse_prime(linenum, line, &dhg))
	continue;
	BN_clear_free(dhg.g);
	BN_clear_free(dhg.p);

	if (dhg.size > max \|\| dhg.size < min)
	continue;

	if ((dhg.size > wantbits && dhg.size < best) \|\|
	(dhg.size > best && best < wantbits)) {
	best = dhg.size;
	bestcount = 0;
	}
	if (dhg.size == best)
	bestcount++;
	}
	rewind(f);

	if (bestcount == 0) {
	fclose(f);
	logit("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
	return (dh_new_group_fallback(max));
	}

	linenum = 0;
	which = arc4random_uniform(bestcount);
	while (fgets(line, sizeof(line), f)) {
	if (!parse_prime(linenum, line, &dhg))
	continue;
	if ((dhg.size > max \|\| dhg.size < min) \|\|
	dhg.size != best \|\|
	linenum++ != which) {
	BN_clear_free(dhg.g);
	BN_clear_free(dhg.p);
	continue;
	}
	break;
	}
	fclose(f);
	if (linenum != which+1) {
	logit("WARNING: line %d disappeared in %s, giving up",
	which, _PATH_DH_PRIMES);
	return (dh_new_group_fallback(max));
	}

	return (dh_new_group(dhg.g, dhg.p));
	}

	/* diffie-hellman-groupN-sha1 */

	int
	dh_pub_is_valid(DH dh, BIGNUM dh_pub)
	{
	int i;
	int n = BN_num_bits(dh_pub);
	int bits_set = 0;
	BIGNUM *tmp;

	if (dh_pub->neg) {
	logit("invalid public DH value: negative");
	return 0;
	}
	if (BN_cmp(dh_pub, BN_value_one()) != 1) { /* pub_exp <= 1 */
	logit("invalid public DH value: <= 1");
	return 0;
	}

	if ((tmp = BN_new()) == NULL) {
	error("%s: BN_new failed", __func__);
	return 0;
	}
	if (!BN_sub(tmp, dh->p, BN_value_one()) \|\|
	BN_cmp(dh_pub, tmp) != -1) { /* pub_exp > p-2 */
	BN_clear_free(tmp);
	logit("invalid public DH value: >= p-1");
	return 0;
	}
	BN_clear_free(tmp);

	for (i = 0; i <= n; i++)
	if (BN_is_bit_set(dh_pub, i))
	bits_set++;
	debug2("bits set: %d/%d", bits_set, BN_num_bits(dh->p));

	/*
	* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial
	*/
	if (bits_set < 4) {
	logit("invalid public DH value (%d/%d)",
	bits_set, BN_num_bits(dh->p));
	return 0;
	}
	return 1;
	}

	int
	dh_gen_key(DH *dh, int need)
	{
	int pbits;

	if (need < 0 \|\| dh->p == NULL \|\|
	(pbits = BN_num_bits(dh->p)) <= 0 \|\|
	need > INT_MAX / 2 \|\| 2 * need > pbits)
	return SSH_ERR_INVALID_ARGUMENT;
	if (need < 256)
	need = 256;
	/*
	* Pollard Rho, Big step/Little Step attacks are O(sqrt(n)),
	* so double requested need here.
	*/
	dh->length = MIN(need * 2, pbits - 1);
	if (DH_generate_key(dh) == 0 \|\|
	!dh_pub_is_valid(dh, dh->pub_key)) {
	BN_clear_free(dh->priv_key);
	return SSH_ERR_LIBCRYPTO_ERROR;
	}
	return 0;
	}

	DH *
	dh_new_group_asc(const char gen, const char modulus)
	{
	DH *dh;

	if ((dh = DH_new()) == NULL)
	return NULL;
	if (BN_hex2bn(&dh->p, modulus) == 0 \|\|
	BN_hex2bn(&dh->g, gen) == 0) {
	DH_free(dh);
	return NULL;
	}
	return (dh);
	}

	/*
	* This just returns the group, we still need to generate the exchange
	* value.
	*/

	DH *
	dh_new_group(BIGNUM gen, BIGNUM modulus)
	{
	DH *dh;

	if ((dh = DH_new()) == NULL)
	return NULL;
	dh->p = modulus;
	dh->g = gen;

	return (dh);
	}

	DH *
	dh_new_group1(void)
	{
	static char gen = "2", group1 =
	"FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
	"29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
	"EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
	"E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
	"EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
	"FFFFFFFF" "FFFFFFFF";

	return (dh_new_group_asc(gen, group1));
	}

	DH *
	dh_new_group14(void)
	{
	static char gen = "2", group14 =
	"FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
	"29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
	"EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
	"E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
	"EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"
	"C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"
	"83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"
	"670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"
	"E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"
	"DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"
	"15728E5A" "8AACAA68" "FFFFFFFF" "FFFFFFFF";

	return (dh_new_group_asc(gen, group14));
	}

	/*
	* 4k bit fallback group used by DH-GEX if moduli file cannot be read.
	* Source: MODP group 16 from RFC3526.
	*/
	DH *
	dh_new_group_fallback(int max)
	{
	static char gen = "2", group16 =
	"FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
	"29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
	"EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
	"E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
	"EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE45B3D"
	"C2007CB8" "A163BF05" "98DA4836" "1C55D39A" "69163FA8" "FD24CF5F"
	"83655D23" "DCA3AD96" "1C62F356" "208552BB" "9ED52907" "7096966D"
	"670C354E" "4ABC9804" "F1746C08" "CA18217C" "32905E46" "2E36CE3B"
	"E39E772C" "180E8603" "9B2783A2" "EC07A28F" "B5C55DF0" "6F4C52C9"
	"DE2BCBF6" "95581718" "3995497C" "EA956AE5" "15D22618" "98FA0510"
	"15728E5A" "8AAAC42D" "AD33170D" "04507A33" "A85521AB" "DF1CBA64"
	"ECFB8504" "58DBEF0A" "8AEA7157" "5D060C7D" "B3970F85" "A6E1E4C7"
	"ABF5AE8C" "DB0933D7" "1E8C94E0" "4A25619D" "CEE3D226" "1AD2EE6B"
	"F12FFA06" "D98A0864" "D8760273" "3EC86A64" "521F2B18" "177B200C"
	"BBE11757" "7A615D6C" "770988C0" "BAD946E2" "08E24FA0" "74E5AB31"
	"43DB5BFC" "E0FD108E" "4B82D120" "A9210801" "1A723C12" "A787E6D7"
	"88719A10" "BDBA5B26" "99C32718" "6AF4E23C" "1A946834" "B6150BDA"
	"2583E9CA" "2AD44CE8" "DBBBC2DB" "04DE8EF9" "2E8EFC14" "1FBECAA6"
	"287C5947" "4E6BC05D" "99B2964F" "A090C3A2" "233BA186" "515BE7ED"
	"1F612970" "CEE2D7AF" "B81BDD76" "2170481C" "D0069127" "D5B05AA9"
	"93B4EA98" "8D8FDDC1" "86FFB7DC" "90A6C08F" "4DF435C9" "34063199"
	"FFFFFFFF" "FFFFFFFF";

	if (max < 4096) {
	debug3("requested max size %d, using 2k bit group 14", max);
	return dh_new_group14();
	}
	debug3("using 4k bit group 16");
	return (dh_new_group_asc(gen, group16));
	}

	/*
	* Estimates the group order for a Diffie-Hellman group that has an
	* attack complexity approximately the same as O(2**bits).
	* Values from NIST Special Publication 800-57: Recommendation for Key
	* Management Part 1 (rev 3) limited by the recommended maximum value
	* from RFC4419 section 3.
	*/

	u_int
	dh_estimate(int bits)
	{
	if (bits <= 112)
	return 2048;
	if (bits <= 128)
	return 3072;
	if (bits <= 192)
	return 7680;
	return 8192;
	}