/*

 * Copyright 1995-2022 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 "bn_local.h"

#define TABLE_SIZE      32

int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,

                     const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m,

                     BN_CTX *ctx, BN_MONT_CTX *in_mont)

{

    int i, j, bits, b, bits1, bits2, ret =

        0, wpos1, wpos2, window1, window2, wvalue1, wvalue2;

    int r_is_one = 1;

    BIGNUM *d, *r;

    const BIGNUM *a_mod_m;

    /* Tables of variables obtained from 'ctx' */

    BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];

    BN_MONT_CTX *mont = NULL;

    bn_check_top(a1);

    bn_check_top(p1);

    bn_check_top(a2);

    bn_check_top(p2);

    bn_check_top(m);

    if (!BN_is_odd(m)) {

        BNerr(BN_F_BN_MOD_EXP2_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);

        return 0;

    }

    bits1 = BN_num_bits(p1);

    bits2 = BN_num_bits(p2);

    if ((bits1 == 0) && (bits2 == 0)) {

        ret = BN_one(rr);

        return ret;

    }

    bits = (bits1 > bits2) ? bits1 : bits2;

    BN_CTX_start(ctx);

    d = BN_CTX_get(ctx);

    r = BN_CTX_get(ctx);

    val1[0] = BN_CTX_get(ctx);

    val2[0] = BN_CTX_get(ctx);

    if (val2[0] == NULL)

        goto err;

    if (in_mont != NULL)

        mont = in_mont;

    else {

        if ((mont = BN_MONT_CTX_new()) == NULL)

            goto err;

        if (!BN_MONT_CTX_set(mont, m, ctx))

            goto err;

    }

    window1 = BN_window_bits_for_exponent_size(bits1);

    window2 = BN_window_bits_for_exponent_size(bits2);

    /*

     * Build table for a1:   val1[i] := a1^(2*i + 1) mod m  for i = 0 .. 2^(window1-1)

     */

    if (a1->neg || BN_ucmp(a1, m) >= 0) {

        if (!BN_mod(val1[0], a1, m, ctx))

            goto err;

        a_mod_m = val1[0];

    } else

        a_mod_m = a1;

    if (BN_is_zero(a_mod_m)) {

        BN_zero(rr);

        ret = 1;

        goto err;

    }

    if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx))

        goto err;

    if (window1 > 1) {

        if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx))

            goto err;

        j = 1 << (window1 - 1);

        for (i = 1; i < j; i++) {

            if (((val1[i] = BN_CTX_get(ctx)) == NULL) ||

                !BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx))

                goto err;

        }

    }

    /*

     * Build table for a2:   val2[i] := a2^(2*i + 1) mod m  for i = 0 .. 2^(window2-1)

     */

    if (a2->neg || BN_ucmp(a2, m) >= 0) {

        if (!BN_mod(val2[0], a2, m, ctx))

            goto err;

        a_mod_m = val2[0];

    } else

        a_mod_m = a2;

    if (BN_is_zero(a_mod_m)) {

        BN_zero(rr);

        ret = 1;

        goto err;

    }

    if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx))

        goto err;

    if (window2 > 1) {

        if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx))

            goto err;

        j = 1 << (window2 - 1);

        for (i = 1; i < j; i++) {

            if (((val2[i] = BN_CTX_get(ctx)) == NULL) ||

                !BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx))

                goto err;

        }

    }

    /* Now compute the power product, using independent windows. */

    r_is_one = 1;

    wvalue1 = 0;                /* The 'value' of the first window */

    wvalue2 = 0;                /* The 'value' of the second window */

    wpos1 = 0;                  /* If wvalue1 > 0, the bottom bit of the

                                 * first window */

    wpos2 = 0;                  /* If wvalue2 > 0, the bottom bit of the

                                 * second window */

    if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))

        goto err;

    for (b = bits - 1; b >= 0; b--) {

        if (!r_is_one) {

            if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))

                goto err;

        }

        if (!wvalue1)

            if (BN_is_bit_set(p1, b)) {

                /*

                 * consider bits b-window1+1 .. b for this window

                 */

                i = b - window1 + 1;

                while (!BN_is_bit_set(p1, i)) /* works for i<0 */

                    i++;

                wpos1 = i;

                wvalue1 = 1;

                for (i = b - 1; i >= wpos1; i--) {

                    wvalue1 <<= 1;

                    if (BN_is_bit_set(p1, i))

                        wvalue1++;

                }

            }

        if (!wvalue2)

            if (BN_is_bit_set(p2, b)) {

                /*

                 * consider bits b-window2+1 .. b for this window

                 */

                i = b - window2 + 1;

                while (!BN_is_bit_set(p2, i))

                    i++;

                wpos2 = i;

                wvalue2 = 1;

                for (i = b - 1; i >= wpos2; i--) {

                    wvalue2 <<= 1;

                    if (BN_is_bit_set(p2, i))

                        wvalue2++;

                }

            }

        if (wvalue1 && b == wpos1) {

            /* wvalue1 is odd and < 2^window1 */

            if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx))

                goto err;

            wvalue1 = 0;

            r_is_one = 0;

        }

        if (wvalue2 && b == wpos2) {

            /* wvalue2 is odd and < 2^window2 */

            if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx))

                goto err;

            wvalue2 = 0;

            r_is_one = 0;

        }

    }

    if (!BN_from_montgomery(rr, r, mont, ctx))

        goto err;

    ret = 1;

 err:

    if (in_mont == NULL)

        BN_MONT_CTX_free(mont);

    BN_CTX_end(ctx);

    bn_check_top(rr);

    return ret;

}