/* $OpenBSD: dh.c,v 1.75 2024/12/03 16:27:53 dtucker 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"

#ifdef WITH_OPENSSL

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

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

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

#include "openbsd-compat/openssl-compat.h"

static const char *moduli_filename;

void dh_set_moduli_file(const char *filename)
{
        moduli_filename = filename;
}

static const char * get_moduli_filename(void)
{
        return moduli_filename ? moduli_filename : _PATH_DH_MODULI;
}

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:
        BN_clear_free(dhg->g);
        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 = NULL;
        size_t linesize = 0;
        int best, bestcount, which, linenum;
        struct dhgroup dhg;

        if ((f = fopen(get_moduli_filename(), "r")) == NULL) {
                logit("WARNING: could not open %s (%s), using fixed modulus",
                    get_moduli_filename(), strerror(errno));
                return (dh_new_group_fallback(max));
        }

        linenum = 0;
        best = bestcount = 0;
        while (getline(&line, &linesize, f) != -1) {
                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++;
        }
        free(line);
        line = NULL;
        linesize = 0;
        rewind(f);

        if (bestcount == 0) {
                fclose(f);
                logit("WARNING: no suitable primes (size %d/%d/%d) in %s",
                    min, wantbits, max, get_moduli_filename());
                return NULL;
        }
        which = arc4random_uniform(bestcount);

        linenum = 0;
        bestcount = 0;
        while (getline(&line, &linesize, f) != -1) {
                linenum++;
                if (!parse_prime(linenum, line, &dhg))
                        continue;
                if ((dhg.size > max || dhg.size < min) ||
                    dhg.size != best ||
                    bestcount++ != which) {
                        BN_clear_free(dhg.g);
                        BN_clear_free(dhg.p);
                        continue;
                }
                break;
        }
        free(line);
        line = NULL;
        fclose(f);
        if (bestcount != which + 1) {
                logit("WARNING: selected prime disappeared in %s, giving up",
                    get_moduli_filename());
                return (dh_new_group_fallback(max));
        }

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

/* diffie-hellman-groupN-sha1 */

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

        DH_get0_pqg(dh, &dh_p, NULL, NULL);

        if (BN_is_negative(dh_pub)) {
                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_f("BN_new failed");
                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;
        const BIGNUM *dh_p, *pub_key;

        DH_get0_pqg(dh, &dh_p, NULL, NULL);

        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.
         */
        if (!DH_set_length(dh, MINIMUM(need * 2, pbits - 1)))
                return SSH_ERR_LIBCRYPTO_ERROR;

        if (DH_generate_key(dh) == 0)
                return SSH_ERR_LIBCRYPTO_ERROR;
        DH_get0_key(dh, &pub_key, NULL);
        if (!dh_pub_is_valid(dh, pub_key))
                return SSH_ERR_INVALID_FORMAT;
        return 0;
}

DH *
dh_new_group_asc(const char *gen, const char *modulus)
{
        DH *dh;
        BIGNUM *dh_p = NULL, *dh_g = NULL;

        if ((dh = DH_new()) == NULL)
                return NULL;
        if (BN_hex2bn(&dh_p, modulus) == 0 ||
            BN_hex2bn(&dh_g, gen) == 0)
                goto fail;
        if (!DH_set0_pqg(dh, dh_p, NULL, dh_g))
                goto fail;
        return dh;
 fail:
        DH_free(dh);
        BN_clear_free(dh_p);
        BN_clear_free(dh_g);
        return NULL;
}

/*
 * 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;
        if (!DH_set0_pqg(dh, modulus, NULL, gen)) {
                DH_free(dh);
                return NULL;
        }

        return dh;
}

/* rfc2409 "Second Oakley Group" (1024 bits) */
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));
}

/* rfc3526 group 14 "2048-bit MODP Group" */
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));
}

/* rfc3526 group 16 "4096-bit MODP Group" */
DH *
dh_new_group16(void)
{
        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";

        return (dh_new_group_asc(gen, group16));
}

/* rfc3526 group 18 "8192-bit MODP Group" */
DH *
dh_new_group18(void)
{
        static char *gen = "2", *group18 =
            "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" "34028492"
            "36C3FAB4" "D27C7026" "C1D4DCB2" "602646DE" "C9751E76" "3DBA37BD"
            "F8FF9406" "AD9E530E" "E5DB382F" "413001AE" "B06A53ED" "9027D831"
            "179727B0" "865A8918" "DA3EDBEB" "CF9B14ED" "44CE6CBA" "CED4BB1B"
            "DB7F1447" "E6CC254B" "33205151" "2BD7AF42" "6FB8F401" "378CD2BF"
            "5983CA01" "C64B92EC" "F032EA15" "D1721D03" "F482D7CE" "6E74FEF6"
            "D55E702F" "46980C82" "B5A84031" "900B1C9E" "59E7C97F" "BEC7E8F3"
            "23A97A7E" "36CC88BE" "0F1D45B7" "FF585AC5" "4BD407B2" "2B4154AA"
            "CC8F6D7E" "BF48E1D8" "14CC5ED2" "0F8037E0" "A79715EE" "F29BE328"
            "06A1D58B" "B7C5DA76" "F550AA3D" "8A1FBFF0" "EB19CCB1" "A313D55C"
            "DA56C9EC" "2EF29632" "387FE8D7" "6E3C0468" "043E8F66" "3F4860EE"
            "12BF2D5B" "0B7474D6" "E694F91E" "6DBE1159" "74A3926F" "12FEE5E4"
            "38777CB6" "A932DF8C" "D8BEC4D0" "73B931BA" "3BC832B6" "8D9DD300"
            "741FA7BF" "8AFC47ED" "2576F693" "6BA42466" "3AAB639C" "5AE4F568"
            "3423B474" "2BF1C978" "238F16CB" "E39D652D" "E3FDB8BE" "FC848AD9"
            "22222E04" "A4037C07" "13EB57A8" "1A23F0C7" "3473FC64" "6CEA306B"
            "4BCBC886" "2F8385DD" "FA9D4B7F" "A2C087E8" "79683303" "ED5BDD3A"
            "062B3CF5" "B3A278A6" "6D2A13F8" "3F44F82D" "DF310EE0" "74AB6A36"
            "4597E899" "A0255DC1" "64F31CC5" "0846851D" "F9AB4819" "5DED7EA1"
            "B1D510BD" "7EE74D73" "FAF36BC3" "1ECFA268" "359046F4" "EB879F92"
            "4009438B" "481C6CD7" "889A002E" "D5EE382B" "C9190DA6" "FC026E47"
            "9558E447" "5677E9AA" "9E3050E2" "765694DF" "C81F56E8" "80B96E71"
            "60C980DD" "98EDD3DF" "FFFFFFFF" "FFFFFFFF";

        return (dh_new_group_asc(gen, group18));
}

/* Select fallback group used by DH-GEX if moduli file cannot be read. */
DH *
dh_new_group_fallback(int max)
{
        debug3_f("requested max size %d", max);
        if (max < 3072) {
                debug3("using 2k bit group 14");
                return dh_new_group14();
        } else if (max < 6144) {
                debug3("using 4k bit group 16");
                return dh_new_group16();
        }
        debug3("using 8k bit group 18");
        return dh_new_group18();
}

/*
 * 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;
}

#endif /* WITH_OPENSSL */