text: /* $OpenBSD: dh.c,v 1.51 2013/07/02 12:31:43 markus 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>
  
  #include <openssl/bn.h>
  #include <openssl/dh.h>
  
  #include <stdarg.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  #include "dh.h"
  #include "pathnames.h"
  #include "log.h"
  #include "misc.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)
  		fatal("parse_prime: BN_new failed");
  	if ((dhg->p = BN_new()) == NULL)
  		fatal("parse_prime: BN_new failed");
  	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;
  	error("Bad prime description in line %d", linenum);
  	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_group14());
  	}
  
  	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_group14());
  	}
  
  	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)
  		fatal("WARNING: line %d disappeared in %s, giving up",
  		    which, _PATH_DH_PRIMES);
  
  	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 > 1)
  		return 1;
  
  	logit("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
  	return 0;
  }
  
  void
  dh_gen_key(DH *dh, int need)
  {
  	int i, bits_set, tries = 0;
  
  	if (need < 0)
  		fatal("dh_gen_key: need < 0");
  	if (dh->p == NULL)
  		fatal("dh_gen_key: dh->p == NULL");
  	if (need > INT_MAX / 2 || 2 * need >= BN_num_bits(dh->p))
  		fatal("dh_gen_key: group too small: %d (2*need %d)",
  		    BN_num_bits(dh->p), 2*need);
  	do {
  		if (dh->priv_key != NULL)
  			BN_clear_free(dh->priv_key);
  		if ((dh->priv_key = BN_new()) == NULL)
  			fatal("dh_gen_key: BN_new failed");
  		/* generate a 2*need bits random private exponent */
  		if (!BN_rand(dh->priv_key, 2*need, 0, 0))
  			fatal("dh_gen_key: BN_rand failed");
  		if (DH_generate_key(dh) == 0)
  			fatal("DH_generate_key");
  		for (i = 0, bits_set = 0; i <= BN_num_bits(dh->priv_key); i++)
  			if (BN_is_bit_set(dh->priv_key, i))
  				bits_set++;
  		debug2("dh_gen_key: priv key bits set: %d/%d",
  		    bits_set, BN_num_bits(dh->priv_key));
  		if (tries++ > 10)
  			fatal("dh_gen_key: too many bad keys: giving up");
  	} while (!dh_pub_is_valid(dh, dh->pub_key));
  }
  
  DH *
  dh_new_group_asc(const char *gen, const char *modulus)
  {
  	DH *dh;
  
  	if ((dh = DH_new()) == NULL)
  		fatal("dh_new_group_asc: DH_new");
  
  	if (BN_hex2bn(&dh->p, modulus) == 0)
  		fatal("BN_hex2bn p");
  	if (BN_hex2bn(&dh->g, gen) == 0)
  		fatal("BN_hex2bn g");
  
  	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)
  		fatal("dh_new_group: DH_new");
  	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));
  }
  
  /*
   * Estimates the group order for a Diffie-Hellman group that has an
   * attack complexity approximately the same as O(2**bits).  Estimate
   * with:  O(exp(1.9223 * (ln q)^(1/3) (ln ln q)^(2/3)))
   */
  
  int
  dh_estimate(int bits)
  {
  
  	if (bits <= 128)
  		return (1024);	/* O(2**86) */
  	if (bits <= 192)
  		return (2048);	/* O(2**116) */
  	return (4096);		/* O(2**156) */
  }
  