source: trunk/third/openssh/dh.c @ 18759

/*
 * 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"
RCSID("$OpenBSD: dh.c,v 1.22 2002/06/27 08:49:44 markus Exp $");

#include "xmalloc.h"

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

#include "buffer.h"
#include "cipher.h"
#include "kex.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;

        cp = line;
        arg = strdelim(&cp);
        /* Ignore leading whitespace */
        if (*arg == '\0')
                arg = strdelim(&cp);
        if (!arg || !*arg || *arg == '#')
                return 0;

        /* time */
        if (cp == NULL || *arg == '\0')
                goto fail;
        arg = strsep(&cp, " "); /* type */
        if (cp == NULL || *arg == '\0')
                goto fail;
        arg = strsep(&cp, " "); /* tests */
        if (cp == NULL || *arg == '\0')
                goto fail;
        arg = strsep(&cp, " "); /* tries */
        if (cp == NULL || *arg == '\0')
                goto fail;
        strsize = strsep(&cp, " "); /* size */
        if (cp == NULL || *strsize == '\0' ||
            (dhg->size = atoi(strsize)) == 0)
                goto fail;
        /* The whole group is one bit larger */
        dhg->size++;
        gen = strsep(&cp, " "); /* gen */
        if (cp == NULL || *gen == '\0')
                goto fail;
        prime = strsep(&cp, " "); /* prime */
        if (cp != NULL || *prime == '\0')
                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)
                goto failclean;

        if (BN_hex2bn(&dhg->p, prime) == 0)
                goto failclean;

        if (BN_num_bits(dhg->p) != dhg->size)
                goto failclean;

        return (1);

 failclean:
        BN_clear_free(dhg->g);
        BN_clear_free(dhg->p);
 fail:
        error("Bad prime description in line %d", linenum);
        return (0);
}

DH *
choose_dh(int min, int wantbits, int max)
{
        FILE *f;
        char line[2048];
        int best, bestcount, which;
        int linenum;
        struct dhgroup dhg;

        if ((f = fopen(_PATH_DH_MODULI, "r")) == NULL &&
            (f = fopen(_PATH_DH_PRIMES, "r")) == NULL) {
                log("WARNING: %s does not exist, using old modulus", _PATH_DH_MODULI);
                return (dh_new_group1());
        }

        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);
                log("WARNING: no suitable primes in %s", _PATH_DH_PRIMES);
                return (NULL);
        }

        linenum = 0;
        which = arc4random() % 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-group1-sha1 */

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

        if (dh_pub->neg) {
                log("invalid public DH value: negativ");
                return 0;
        }
        for (i = 0; i <= n; i++)
                if (BN_is_bit_set(dh_pub, i))
                        bits_set++;
        debug("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 && (BN_cmp(dh_pub, dh->p) == -1))
                return 1;
        log("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 = 0, tries = 0;

        if (dh->p == NULL)
                fatal("dh_gen_key: dh->p == NULL");
        if (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; i <= BN_num_bits(dh->priv_key); i++)
                        if (BN_is_bit_set(dh->priv_key, i))
                                bits_set++;
                debug("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));
}

/*
 * 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 < 64)
                return (512);   /* O(2**63) */
        if (bits < 128)
                return (1024);  /* O(2**86) */
        if (bits < 192)
                return (2048);  /* O(2**116) */
        return (4096);          /* O(2**156) */
}