text: /*
   * Copyright 1995-2018 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 "internal/constant_time_locl.h"
  
  #include <stdio.h>
  #include "internal/cryptlib.h"
  #include <openssl/bn.h>
  #include <openssl/rsa.h>
  #include <openssl/rand.h>
  
  int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
                                   const unsigned char *from, int flen)
  {
      int j;
      unsigned char *p;
  
      if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
          RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,
                 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
          return 0;
      }
  
      p = (unsigned char *)to;
  
      *(p++) = 0;
      *(p++) = 1;                 /* Private Key BT (Block Type) */
  
      /* pad out with 0xff data */
      j = tlen - 3 - flen;
      memset(p, 0xff, j);
      p += j;
      *(p++) = '\0';
      memcpy(p, from, (unsigned int)flen);
      return 1;
  }
  
  int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
                                     const unsigned char *from, int flen,
                                     int num)
  {
      int i, j;
      const unsigned char *p;
  
      p = from;
  
      /*
       * The format is
       * 00 || 01 || PS || 00 || D
       * PS - padding string, at least 8 bytes of FF
       * D  - data.
       */
  
      if (num < 11)
          return -1;
  
      /* Accept inputs with and without the leading 0-byte. */
      if (num == flen) {
          if ((*p++) != 0x00) {
              RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                     RSA_R_INVALID_PADDING);
              return -1;
          }
          flen--;
      }
  
      if ((num != (flen + 1)) || (*(p++) != 0x01)) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                 RSA_R_BLOCK_TYPE_IS_NOT_01);
          return -1;
      }
  
      /* scan over padding data */
      j = flen - 1;               /* one for type. */
      for (i = 0; i < j; i++) {
          if (*p != 0xff) {       /* should decrypt to 0xff */
              if (*p == 0) {
                  p++;
                  break;
              } else {
                  RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                         RSA_R_BAD_FIXED_HEADER_DECRYPT);
                  return -1;
              }
          }
          p++;
      }
  
      if (i == j) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                 RSA_R_NULL_BEFORE_BLOCK_MISSING);
          return -1;
      }
  
      if (i < 8) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
                 RSA_R_BAD_PAD_BYTE_COUNT);
          return -1;
      }
      i++;                        /* Skip over the '\0' */
      j -= i;
      if (j > tlen) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
          return -1;
      }
      memcpy(to, p, (unsigned int)j);
  
      return j;
  }
  
  int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
                                   const unsigned char *from, int flen)
  {
      int i, j;
      unsigned char *p;
  
      if (flen > (tlen - 11)) {
          RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2,
                 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 - 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++;
      }
  
      *(p++) = '\0';
  
      memcpy(p, from, (unsigned int)flen);
      return 1;
  }
  
  int RSA_padding_check_PKCS1_type_2(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;
      int zero_index = 0, msg_index, mlen = -1;
  
      if (tlen <= 0 || flen <= 0)
          return -1;
  
      /*
       * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
       * section 7.2.2.
       */
  
      if (flen > num || num < 11) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
                 RSA_R_PKCS_DECODING_ERROR);
          return -1;
      }
  
      em = OPENSSL_malloc(num);
      if (em == NULL) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, 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;
      }
      from = em;
  
      good = constant_time_is_zero(from[0]);
      good &= constant_time_eq(from[1], 2);
  
      /* scan over padding data */
      found_zero_byte = 0;
      for (i = 2; i < num; i++) {
          unsigned int equals0 = constant_time_is_zero(from[i]);
  
          zero_index = constant_time_select_int(~found_zero_byte & equals0,
                                                i, zero_index);
          found_zero_byte |= equals0;
      }
  
      /*
       * PS must be at least 8 bytes long, and it starts two bytes into |from|.
       * 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);
  
      /*
       * 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);
  
      /*
       * Even though we can't fake result's length, we can pretend copying
       * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
       * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
       * where |mlen'| is "saturated" |mlen| value. Deducing information
       * about failure or |mlen| would take attacker's ability to observe
       * memory access pattern with byte granularity *as it occurs*. It
       * should be noted that failure is indistinguishable from normal
       * operation if |tlen| is fixed by protocol.
       */
      tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
      msg_index = constant_time_select_int(good, msg_index, num - tlen);
      mlen = num - msg_index;
      for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
          unsigned int equals = constant_time_eq(i, mlen);
  
          from -= tlen & equals;  /* if (i == mlen) rewind   */
          mask &= mask ^ equals;  /* if (i == mlen) mask = 0 */
          to[i] = constant_time_select_8(mask, from[i], to[i]);
      }
  
      OPENSSL_clear_free(em, num);
      RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
      err_clear_last_constant_time(1 & good);
  
      return constant_time_select_int(good, mlen, -1);
  }
  