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 /*
  11  * RSA low level APIs are deprecated for public use, but still ok for
  12  * internal use.
  13  */
  14 #include "internal/deprecated.h"
  15
  16 #include <stdio.h>
  17 #include "internal/cryptlib.h"
  18 #include <openssl/bn.h>
  19 #include <openssl/rsa.h>
  20 #include <openssl/rand.h>
  21 #include "internal/constant_time.h"
  22
  23 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
  24                            const unsigned char *from, int flen)
  25 {
  26     int i, j;
  27     unsigned char *p;
  28
  29     if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
  30         RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
  31                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  32         return 0;
  33     }
  34
  35     p = (unsigned char *)to;
  36
  37     *(p++) = 0;
  38     *(p++) = 2;                 /* Public Key BT (Block Type) */
  39
  40     /* pad out with non-zero random data */
  41     j = tlen - 3 - 8 - flen;
  42
  43     if (RAND_bytes(p, j) <= 0)
  44         return 0;
  45     for (i = 0; i < j; i++) {
  46         if (*p == '\0')
  47             do {
  48                 if (RAND_bytes(p, 1) <= 0)
  49                     return 0;
  50             } while (*p == '\0');
  51         p++;
  52     }
  53
  54     memset(p, 3, 8);
  55     p += 8;
  56     *(p++) = '\0';
  57
  58     memcpy(p, from, (unsigned int)flen);
  59     return 1;
  60 }
  61
  62 /*
  63  * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
  64  * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
  65  * preserves error code reporting for backward compatibility.
  66  */
  67 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
  68                              const unsigned char *from, int flen, int num)
  69 {
  70     int i;
  71     /* |em| is the encoded message, zero-padded to exactly |num| bytes */
  72     unsigned char *em = NULL;
  73     unsigned int good, found_zero_byte, mask, threes_in_row;
  74     int zero_index = 0, msg_index, mlen = -1, err;
  75
  76     if (tlen <= 0 || flen <= 0)
  77         return -1;
  78
  79     if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
  80         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
  81         return -1;
  82     }
  83
  84     em = OPENSSL_malloc(num);
  85     if (em == NULL) {
  86         RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
  87         return -1;
  88     }
  89     /*
  90      * Caller is encouraged to pass zero-padded message created with
  91      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
  92      * bounds, it's impossible to have an invariant memory access pattern
  93      * in case |from| was not zero-padded in advance.
  94      */
  95     for (from += flen, em += num, i = 0; i < num; i++) {
  96         mask = ~constant_time_is_zero(flen);
  97         flen -= 1 & mask;
  98         from -= 1 & mask;
  99         *--em = *from & mask;
 100     }
 101
 102     good = constant_time_is_zero(em[0]);
 103     good &= constant_time_eq(em[1], 2);
 104     err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
 105     mask = ~good;
 106
 107     /* scan over padding data */
 108     found_zero_byte = 0;
 109     threes_in_row = 0;
 110     for (i = 2; i < num; i++) {
 111         unsigned int equals0 = constant_time_is_zero(em[i]);
 112
 113         zero_index = constant_time_select_int(~found_zero_byte & equals0,
 114                                               i, zero_index);
 115         found_zero_byte |= equals0;
 116
 117         threes_in_row += 1 & ~found_zero_byte;
 118         threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
 119     }
 120
 121     /*
 122      * PS must be at least 8 bytes long, and it starts two bytes into |em|.
 123      * If we never found a 0-byte, then |zero_index| is 0 and the check
 124      * also fails.
 125      */
 126     good &= constant_time_ge(zero_index, 2 + 8);
 127     err = constant_time_select_int(mask | good, err,
 128                                    RSA_R_NULL_BEFORE_BLOCK_MISSING);
 129     mask = ~good;
 130
 131     good &= constant_time_ge(threes_in_row, 8);
 132     err = constant_time_select_int(mask | good, err,
 133                                    RSA_R_SSLV3_ROLLBACK_ATTACK);
 134     mask = ~good;
 135
 136     /*
 137      * Skip the zero byte. This is incorrect if we never found a zero-byte
 138      * but in this case we also do not copy the message out.
 139      */
 140     msg_index = zero_index + 1;
 141     mlen = num - msg_index;
 142
 143     /*
 144      * For good measure, do this check in constant time as well.
 145      */
 146     good &= constant_time_ge(tlen, mlen);
 147     err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
 148
 149     /*
 150      * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
 151      * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
 152      * Otherwise leave |to| unchanged.
 153      * Copy the memory back in a way that does not reveal the size of
 154      * the data being copied via a timing side channel. This requires copying
 155      * parts of the buffer multiple times based on the bits set in the real
 156      * length. Clear bits do a non-copy with identical access pattern.
 157      * The loop below has overall complexity of O(N*log(N)).
 158      */
 159     tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
 160                                     num - RSA_PKCS1_PADDING_SIZE, tlen);
 161     for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
 162         mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
 163         for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
 164             em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
 165     }
 166     for (i = 0; i < tlen; i++) {
 167         mask = good & constant_time_lt(i, mlen);
 168         to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
 169     }
 170
 171     OPENSSL_clear_free(em, num);
 172     RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
 173     err_clear_last_constant_time(1 & good);
 174
 175     return constant_time_select_int(good, mlen, -1);
 176 }