/*

 * 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 <openssl/bn.h>

#include <openssl/rsa.h>

#include <openssl/rand.h>

#include "internal/constant_time.h"

int RSA_padding_add_SSLv23(unsigned char *to, int tlen,

                           const unsigned char *from, int flen)

{

    int i, j;

    unsigned char *p;

    if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {

        RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,

               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);

        return 0;

    }

    p = (unsigned char *)to;

    *(p++) = 0;

    *(p++) = 2;                 /* Public Key BT (Block Type) */

    /* pad out with non-zero random data */

    j = tlen - 3 - 8 - flen;

    if (RAND_bytes(p, j) <= 0)

        return 0;

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

        if (*p == '\0')

            do {

                if (RAND_bytes(p, 1) <= 0)

                    return 0;

            } while (*p == '\0');

        p++;

    }

    memset(p, 3, 8);

    p += 8;

    *(p++) = '\0';

    memcpy(p, from, (unsigned int)flen);

    return 1;

}

/*

 * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding

 * if nul delimiter is preceded by 8 consecutive 0x03 bytes. It also

 * preserves error code reporting for backward compatibility.

 */

int RSA_padding_check_SSLv23(unsigned char *to, int tlen,

                             const unsigned char *from, int flen, int num)

{

    int i;

    /* |em| is the encoded message, zero-padded to exactly |num| bytes */

    unsigned char *em = NULL;

    unsigned int good, found_zero_byte, mask, threes_in_row;

    int zero_index = 0, msg_index, mlen = -1, err;

    if (tlen <= 0 || flen <= 0)

        return -1;

    if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {

        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);

        return -1;

    }

    em = OPENSSL_malloc(num);

    if (em == NULL) {

        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);

        return -1;

    }

    /*

     * Caller is encouraged to pass zero-padded message created with

     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s

     * bounds, it's impossible to have an invariant memory access pattern

     * in case |from| was not zero-padded in advance.

     */

    for (from += flen, em += num, i = 0; i < num; i++) {

        mask = ~constant_time_is_zero(flen);

        flen -= 1 & mask;

        from -= 1 & mask;

        *--em = *from & mask;

    }

    good = constant_time_is_zero(em[0]);

    good &= constant_time_eq(em[1], 2);

    err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);

    mask = ~good;

    /* scan over padding data */

    found_zero_byte = 0;

    threes_in_row = 0;

    for (i = 2; i < num; i++) {

        unsigned int equals0 = constant_time_is_zero(em[i]);

        zero_index = constant_time_select_int(~found_zero_byte & equals0,

                                              i, zero_index);

        found_zero_byte |= equals0;

        threes_in_row += 1 & ~found_zero_byte;

        threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);

    }

    /*

     * PS must be at least 8 bytes long, and it starts two bytes into |em|.

     * If we never found a 0-byte, then |zero_index| is 0 and the check

     * also fails.

     */

    good &= constant_time_ge(zero_index, 2 + 8);

    err = constant_time_select_int(mask | good, err,

                                   RSA_R_NULL_BEFORE_BLOCK_MISSING);

    mask = ~good;

    /*

     * Reject if nul delimiter is preceded by 8 consecutive 0x03 bytes. Note

     * that RFC5246 incorrectly states this the other way around, i.e. reject

     * if it is not preceded by 8 consecutive 0x03 bytes. However this is

     * corrected in subsequent errata for that RFC.

     */

    good &= constant_time_lt(threes_in_row, 8);

    err = constant_time_select_int(mask | good, err,

                                   RSA_R_SSLV3_ROLLBACK_ATTACK);

    mask = ~good;

    /*

     * Skip the zero byte. This is incorrect if we never found a zero-byte

     * but in this case we also do not copy the message out.

     */

    msg_index = zero_index + 1;

    mlen = num - msg_index;

    /*

     * For good measure, do this check in constant time as well.

     */

    good &= constant_time_ge(tlen, mlen);

    err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);

    /*

     * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.

     * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.

     * Otherwise leave |to| unchanged.

     * Copy the memory back in a way that does not reveal the size of

     * the data being copied via a timing side channel. This requires copying

     * parts of the buffer multiple times based on the bits set in the real

     * length. Clear bits do a non-copy with identical access pattern.

     * The loop below has overall complexity of O(N*log(N)).

     */

    tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),

                                    num - RSA_PKCS1_PADDING_SIZE, tlen);

    for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {

        mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);

        for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)

            em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);

    }

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

        mask = good & constant_time_lt(i, mlen);

        to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);

    }

    OPENSSL_clear_free(em, num);

    RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);

    err_clear_last_constant_time(1 & good);

    return constant_time_select_int(good, mlen, -1);

}