text: /*
   * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
   *
   * Licensed under the Apache License 2.0 (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
   */
  
  /*
   * RSA low level APIs are deprecated for public use, but still ok for
   * internal use.
   */
  #include "internal/deprecated.h"
  
  #include <stdio.h>
  #include "internal/cryptlib.h"
  #include <openssl/bn.h>
  #include <openssl/rsa.h>
  #include <openssl/rand.h>
  #include "internal/constant_time.h"
  #include "rsa_local.h"
  
  int rsa_padding_add_SSLv23_ex(OPENSSL_CTX *libctx, 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(0, 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_ex(libctx, p, j) <= 0)
          return 0;
      for (i = 0; i < j; i++) {
          if (*p == '\0')
              do {
                  if (RAND_bytes_ex(libctx, 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;
  }
  
  int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
                             const unsigned char *from, int flen)
  {
      return rsa_padding_add_SSLv23_ex(NULL, to, tlen, from, flen);
  }
  
  /*
   * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
   * if nul delimiter is not 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;
  
      good &= constant_time_ge(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);
  }
  