/*

 * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include <stdio.h>

#include "internal/cryptlib.h"

#include "dh_local.h"

#include "crypto/bn.h"

static int generate_key(DH *dh);

static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);

static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,

                         const BIGNUM *a, const BIGNUM *p,

                         const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);

static int dh_init(DH *dh);

static int dh_finish(DH *dh);

int DH_generate_key(DH *dh)

{

    return dh->meth->generate_key(dh);

}

/*-

 * NB: This function is inherently not constant time due to the

 * RFC 5246 (8.1.2) padding style that strips leading zero bytes.

 */

int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)

{

    int ret = 0, i;

    volatile size_t npad = 0, mask = 1;

    /* compute the key; ret is constant unless compute_key is external */

    if ((ret = dh->meth->compute_key(key, pub_key, dh)) <= 0)

        return ret;

    /* count leading zero bytes, yet still touch all bytes */

    for (i = 0; i < ret; i++) {

        mask &= !key[i];

        npad += mask;

    }

    /* unpad key */

    ret -= npad;

    /* key-dependent memory access, potentially leaking npad / ret */

    memmove(key, key + npad, ret);

    /* key-dependent memory access, potentially leaking npad / ret */

    memset(key + ret, 0, npad);

    return ret;

}

int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)

{

    int rv, pad;

    /* rv is constant unless compute_key is external */

    rv = dh->meth->compute_key(key, pub_key, dh);

    if (rv <= 0)

        return rv;

    pad = BN_num_bytes(dh->p) - rv;

    /* pad is constant (zero) unless compute_key is external */

    if (pad > 0) {

        memmove(key + pad, key, rv);

        memset(key, 0, pad);

    }

    return rv + pad;

}

static DH_METHOD dh_ossl = {

    "OpenSSL DH Method",

    generate_key,

    compute_key,

    dh_bn_mod_exp,

    dh_init,

    dh_finish,

    DH_FLAG_FIPS_METHOD,

    NULL,

    NULL

};

static const DH_METHOD *default_DH_method = &dh_ossl;

const DH_METHOD *DH_OpenSSL(void)

{

    return &dh_ossl;

}

void DH_set_default_method(const DH_METHOD *meth)

{

    default_DH_method = meth;

}

const DH_METHOD *DH_get_default_method(void)

{

    return default_DH_method;

}

static int generate_key(DH *dh)

{

    int ok = 0;

    int generate_new_key = 0;

    unsigned l;

    BN_CTX *ctx = NULL;

    BN_MONT_CTX *mont = NULL;

    BIGNUM *pub_key = NULL, *priv_key = NULL;

    if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {

        DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);

        return 0;

    }

    ctx = BN_CTX_new();

    if (ctx == NULL)

        goto err;

    if (dh->priv_key == NULL) {

        priv_key = BN_secure_new();

        if (priv_key == NULL)

            goto err;

        generate_new_key = 1;

    } else

        priv_key = dh->priv_key;

    if (dh->pub_key == NULL) {

        pub_key = BN_new();

        if (pub_key == NULL)

            goto err;

    } else

        pub_key = dh->pub_key;

    if (dh->flags & DH_FLAG_CACHE_MONT_P) {

        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,

                                      dh->lock, dh->p, ctx);

        if (!mont)

            goto err;

    }

    if (generate_new_key) {

        if (dh->q) {

            do {

                if (!BN_priv_rand_range(priv_key, dh->q))

                    goto err;

            }

            while (BN_is_zero(priv_key) || BN_is_one(priv_key));

        } else {

            /* secret exponent length */

            l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;

            if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))

                goto err;

            /*

             * We handle just one known case where g is a quadratic non-residue:

             * for g = 2: p % 8 == 3

             */

            if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) {

                /* clear bit 0, since it won't be a secret anyway */

                if (!BN_clear_bit(priv_key, 0))

                    goto err;

            }

        }

    }

    {

        BIGNUM *prk = BN_new();

        if (prk == NULL)

            goto err;

        BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);

        if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {

            BN_clear_free(prk);

            goto err;

        }

        /* We MUST free prk before any further use of priv_key */

        BN_clear_free(prk);

    }

    dh->pub_key = pub_key;

    dh->priv_key = priv_key;

    ok = 1;

 err:

    if (ok != 1)

        DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);

    if (pub_key != dh->pub_key)

        BN_free(pub_key);

    if (priv_key != dh->priv_key)

        BN_free(priv_key);

    BN_CTX_free(ctx);

    return ok;

}

static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)

{

    BN_CTX *ctx = NULL;

    BN_MONT_CTX *mont = NULL;

    BIGNUM *tmp;

    int ret = -1;

    int check_result;

    if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {

        DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);

        goto err;

    }

    ctx = BN_CTX_new();

    if (ctx == NULL)

        goto err;

    BN_CTX_start(ctx);

    tmp = BN_CTX_get(ctx);

    if (tmp == NULL)

        goto err;

    if (dh->priv_key == NULL) {

        DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);

        goto err;

    }

    if (dh->flags & DH_FLAG_CACHE_MONT_P) {

        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,

                                      dh->lock, dh->p, ctx);

        BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);

        if (!mont)

            goto err;

    }

    if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {

        DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);

        goto err;

    }

    if (!dh->

        meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {

        DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);

        goto err;

    }

    ret = BN_bn2binpad(tmp, key, BN_num_bytes(dh->p));

 err:

    BN_CTX_end(ctx);

    BN_CTX_free(ctx);

    return ret;

}

static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,

                         const BIGNUM *a, const BIGNUM *p,

                         const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)

{

    return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);

}

static int dh_init(DH *dh)

{

    dh->flags |= DH_FLAG_CACHE_MONT_P;

    return 1;

}

static int dh_finish(DH *dh)

{

    BN_MONT_CTX_free(dh->method_mont_p);

    return 1;

}