crypto/rsa/rsa_ssl.c

   1 /*
   2  * Copyright 1995-2018 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_locl.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 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 (flen < 10) {
  71         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
  72         return -1;
  73     }
  74
  75     em = OPENSSL_malloc(num);
  76     if (em == NULL) {
  77         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
  78         return -1;
  79     }
  80     /*
  81      * Caller is encouraged to pass zero-padded message created with
  82      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
  83      * bounds, it's impossible to have an invariant memory access pattern
  84      * in case |from| was not zero-padded in advance.
  85      */
  86     for (from += flen, em += num, i = 0; i < num; i++) {
  87         mask = ~constant_time_is_zero(flen);
  88         flen -= 1 & mask;
  89         from -= 1 & mask;
  90         *--em = *from & mask;
  91     }
  92     from = em;
  93
  94     good = constant_time_is_zero(from[0]);
  95     good &= constant_time_eq(from[1], 2);
  96     err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
  97     mask = ~good;
  98
  99     /* scan over padding data */
 100     found_zero_byte = 0;
 101     threes_in_row = 0;
 102     for (i = 2; i < num; i++) {
 103         unsigned int equals0 = constant_time_is_zero(from[i]);
 104
 105         zero_index = constant_time_select_int(~found_zero_byte & equals0,
 106                                               i, zero_index);
 107         found_zero_byte |= equals0;
 108
 109         threes_in_row += 1 & ~found_zero_byte;
 110         threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
 111     }
 112
 113     /*
 114      * PS must be at least 8 bytes long, and it starts two bytes into |from|.
 115      * If we never found a 0-byte, then |zero_index| is 0 and the check
 116      * also fails.
 117      */
 118     good &= constant_time_ge(zero_index, 2 + 8);
 119     err = constant_time_select_int(mask | good, err,
 120                                    RSA_R_NULL_BEFORE_BLOCK_MISSING);
 121     mask = ~good;
 122
 123     good &= constant_time_lt(threes_in_row, 8);
 124     err = constant_time_select_int(mask | good, err,
 125                                    RSA_R_SSLV3_ROLLBACK_ATTACK);
 126     mask = ~good;
 127
 128     /*
 129      * Skip the zero byte. This is incorrect if we never found a zero-byte
 130      * but in this case we also do not copy the message out.
 131      */
 132     msg_index = zero_index + 1;
 133     mlen = num - msg_index;
 134
 135     /*
 136      * For good measure, do this check in constant time as well.
 137      */
 138     good &= constant_time_ge(tlen, mlen);
 139     err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
 140
 141     /*
 142      * Even though we can't fake result's length, we can pretend copying
 143      * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
 144      * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
 145      * where |mlen'| is "saturated" |mlen| value. Deducing information
 146      * about failure or |mlen| would take attacker's ability to observe
 147      * memory access pattern with byte granularity *as it occurs*. It
 148      * should be noted that failure is indistinguishable from normal
 149      * operation if |tlen| is fixed by protocol.
 150      */
 151     tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
 152     msg_index = constant_time_select_int(good, msg_index, num - tlen);
 153     mlen = num - msg_index;
 154     for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
 155         unsigned int equals = constant_time_eq(i, mlen);
 156
 157         from -= tlen & equals;  /* if (i == mlen) rewind   */
 158         mask &= mask ^ equals;  /* if (i == mlen) mask = 0 */
 159         to[i] = constant_time_select_8(mask, from[i], to[i]);
 160     }
 161
 162     OPENSSL_clear_free(em, num);
 163     RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
 164     err_clear_last_constant_time(1 & good);
 165
 166     return constant_time_select_int(good, mlen, -1);
 167 }