crypto/rsa/rsa_ssl.c

   1 /*
   2  * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include <stdio.h>
  11 #include "internal/cryptlib.h"
  12 #include <openssl/bn.h>
  13 #include <openssl/rsa.h>
  14 #include <openssl/rand.h>
  15 #include "internal/constant_time.h"
  16
  17 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
  18                            const unsigned char *from, int flen)
  19 {
  20     int i, j;
  21     unsigned char *p;
  22
  23     if (flen > (tlen - 11)) {
  24         RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
  25                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  26         return 0;
  27     }
  28
  29     p = (unsigned char *)to;
  30
  31     *(p++) = 0;
  32     *(p++) = 2;                 /* Public Key BT (Block Type) */
  33
  34     /* pad out with non-zero random data */
  35     j = tlen - 3 - 8 - flen;
  36
  37     if (RAND_bytes(p, j) <= 0)
  38         return 0;
  39     for (i = 0; i < j; i++) {
  40         if (*p == '\0')
  41             do {
  42                 if (RAND_bytes(p, 1) <= 0)
  43                     return 0;
  44             } while (*p == '\0');
  45         p++;
  46     }
  47
  48     memset(p, 3, 8);
  49     p += 8;
  50     *(p++) = '\0';
  51
  52     memcpy(p, from, (unsigned int)flen);
  53     return 1;
  54 }
  55
  56 /*
  57  * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
  58  * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
  59  * preserves error code reporting for backward compatibility.
  60  */
  61 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
  62                              const unsigned char *from, int flen, int num)
  63 {
  64     int i;
  65     /* |em| is the encoded message, zero-padded to exactly |num| bytes */
  66     unsigned char *em = NULL;
  67     unsigned int good, found_zero_byte, mask, threes_in_row;
  68     int zero_index = 0, msg_index, mlen = -1, err;
  69
  70     if (tlen <= 0 || flen <= 0)
  71         return -1;
  72
  73     if (flen > num || num < 11) {
  74         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
  75         return -1;
  76     }
  77
  78     em = OPENSSL_malloc(num);
  79     if (em == NULL) {
  80         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
  81         return -1;
  82     }
  83     /*
  84      * Caller is encouraged to pass zero-padded message created with
  85      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
  86      * bounds, it's impossible to have an invariant memory access pattern
  87      * in case |from| was not zero-padded in advance.
  88      */
  89     for (from += flen, em += num, i = 0; i < num; i++) {
  90         mask = ~constant_time_is_zero(flen);
  91         flen -= 1 & mask;
  92         from -= 1 & mask;
  93         *--em = *from & mask;
  94     }
  95
  96     good = constant_time_is_zero(em[0]);
  97     good &= constant_time_eq(em[1], 2);
  98     err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
  99     mask = ~good;
 100
 101     /* scan over padding data */
 102     found_zero_byte = 0;
 103     threes_in_row = 0;
 104     for (i = 2; i < num; i++) {
 105         unsigned int equals0 = constant_time_is_zero(em[i]);
 106
 107         zero_index = constant_time_select_int(~found_zero_byte & equals0,
 108                                               i, zero_index);
 109         found_zero_byte |= equals0;
 110
 111         threes_in_row += 1 & ~found_zero_byte;
 112         threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
 113     }
 114
 115     /*
 116      * PS must be at least 8 bytes long, and it starts two bytes into |em|.
 117      * If we never found a 0-byte, then |zero_index| is 0 and the check
 118      * also fails.
 119      */
 120     good &= constant_time_ge(zero_index, 2 + 8);
 121     err = constant_time_select_int(mask | good, err,
 122                                    RSA_R_NULL_BEFORE_BLOCK_MISSING);
 123     mask = ~good;
 124
 125     good &= constant_time_ge(threes_in_row, 8);
 126     err = constant_time_select_int(mask | good, err,
 127                                    RSA_R_SSLV3_ROLLBACK_ATTACK);
 128     mask = ~good;
 129
 130     /*
 131      * Skip the zero byte. This is incorrect if we never found a zero-byte
 132      * but in this case we also do not copy the message out.
 133      */
 134     msg_index = zero_index + 1;
 135     mlen = num - msg_index;
 136
 137     /*
 138      * For good measure, do this check in constant time as well.
 139      */
 140     good &= constant_time_ge(tlen, mlen);
 141     err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
 142
 143     /*
 144      * Move the result in-place by |num|-11-|mlen| bytes to the left.
 145      * Then if |good| move |mlen| bytes from |em|+11 to |to|.
 146      * Otherwise leave |to| unchanged.
 147      * Copy the memory back in a way that does not reveal the size of
 148      * the data being copied via a timing side channel. This requires copying
 149      * parts of the buffer multiple times based on the bits set in the real
 150      * length. Clear bits do a non-copy with identical access pattern.
 151      * The loop below has overall complexity of O(N*log(N)).
 152      */
 153     tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
 154                                     num - 11, tlen);
 155     for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) {
 156         mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0);
 157         for (i = 11; i < num - msg_index; i++)
 158             em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
 159     }
 160     for (i = 0; i < tlen; i++) {
 161         mask = good & constant_time_lt(i, mlen);
 162         to[i] = constant_time_select_8(mask, em[i + 11], to[i]);
 163     }
 164
 165     OPENSSL_clear_free(em, num);
 166     RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
 167     err_clear_last_constant_time(1 & good);
 168
 169     return constant_time_select_int(good, mlen, -1);
 170 }