static int generate_key(DH *dh)
{
    int ok = 0;
    int generate_new_key = 0;
    unsigned l;
    BN_CTX *ctx;
    BN_MONT_CTX *mont = NULL;
    BIGNUM *pub_key = NULL, *priv_key = NULL;

    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_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_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
                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_free(prk);
            goto err;
        }
        /* We MUST free prk before any further use of priv_key */
        BN_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 generate_key(DH *dh)
{
    int ok = 0;
    int generate_new_key = 0;
    unsigned l;
    BN_CTX *ctx;
    BN_MONT_CTX *mont = NULL;
    BIGNUM *pub_key = NULL, *priv_key = NULL;

    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_rand_range(priv_key, dh->q))
                    goto err;
            }
            while (BN_is_zero(priv_key) || BN_is_one(priv_key));
        } else {
             
            l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
            if (!BN_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
                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_free(prk);
            goto err;
        }
         
        BN_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);
}