crypto/rsa/rsa_ssl.c

   1 /*
   2  * Copyright 1995-2021 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 #include "rsa_local.h"
  23
  24 int ossl_rsa_padding_add_SSLv23_ex(OSSL_LIB_CTX *libctx, unsigned char *to,
  25                                    int tlen, const unsigned char *from,
  26                                    int flen)
  27 {
  28     int i, j;
  29     unsigned char *p;
  30
  31     if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
  32         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  33         return 0;
  34     }
  35
  36     p = (unsigned char *)to;
  37
  38     *(p++) = 0;
  39     *(p++) = 2;                 /* Public Key BT (Block Type) */
  40
  41     /* pad out with non-zero random data */
  42     j = tlen - 3 - 8 - flen;
  43
  44     if (RAND_bytes_ex(libctx, p, j) <= 0)
  45         return 0;
  46     for (i = 0; i < j; i++) {
  47         if (*p == '\0')
  48             do {
  49                 if (RAND_bytes_ex(libctx, p, 1) <= 0)
  50                     return 0;
  51             } while (*p == '\0');
  52         p++;
  53     }
  54
  55     memset(p, 3, 8);
  56     p += 8;
  57     *(p++) = '\0';
  58
  59     memcpy(p, from, (unsigned int)flen);
  60     return 1;
  61 }
  62
  63 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
  64                            const unsigned char *from, int flen)
  65 {
  66     return ossl_rsa_padding_add_SSLv23_ex(NULL, to, tlen, from, flen);
  67 }
  68
  69 /*
  70  * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
  71  * if nul delimiter is preceded by 8 consecutive 0x03 bytes. It also
  72  * preserves error code reporting for backward compatibility.
  73  */
  74 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
  75                              const unsigned char *from, int flen, int num)
  76 {
  77     int i;
  78     /* |em| is the encoded message, zero-padded to exactly |num| bytes */
  79     unsigned char *em = NULL;
  80     unsigned int good, found_zero_byte, mask, threes_in_row;
  81     int zero_index = 0, msg_index, mlen = -1, err;
  82
  83     if (tlen <= 0 || flen <= 0)
  84         return -1;
  85
  86     if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
  87         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_SMALL);
  88         return -1;
  89     }
  90
  91     em = OPENSSL_malloc(num);
  92     if (em == NULL) {
  93         ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
  94         return -1;
  95     }
  96     /*
  97      * Caller is encouraged to pass zero-padded message created with
  98      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
  99      * bounds, it's impossible to have an invariant memory access pattern
 100      * in case |from| was not zero-padded in advance.
 101      */
 102     for (from += flen, em += num, i = 0; i < num; i++) {
 103         mask = ~constant_time_is_zero(flen);
 104         flen -= 1 & mask;
 105         from -= 1 & mask;
 106         *--em = *from & mask;
 107     }
 108
 109     good = constant_time_is_zero(em[0]);
 110     good &= constant_time_eq(em[1], 2);
 111     err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
 112     mask = ~good;
 113
 114     /* scan over padding data */
 115     found_zero_byte = 0;
 116     threes_in_row = 0;
 117     for (i = 2; i < num; i++) {
 118         unsigned int equals0 = constant_time_is_zero(em[i]);
 119
 120         zero_index = constant_time_select_int(~found_zero_byte & equals0,
 121                                               i, zero_index);
 122         found_zero_byte |= equals0;
 123
 124         threes_in_row += 1 & ~found_zero_byte;
 125         threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
 126     }
 127
 128     /*
 129      * PS must be at least 8 bytes long, and it starts two bytes into |em|.
 130      * If we never found a 0-byte, then |zero_index| is 0 and the check
 131      * also fails.
 132      */
 133     good &= constant_time_ge(zero_index, 2 + 8);
 134     err = constant_time_select_int(mask | good, err,
 135                                    RSA_R_NULL_BEFORE_BLOCK_MISSING);
 136     mask = ~good;
 137
 138     /*
 139      * Reject if nul delimiter is preceded by 8 consecutive 0x03 bytes. Note
 140      * that RFC5246 incorrectly states this the other way around, i.e. reject
 141      * if it is not preceded by 8 consecutive 0x03 bytes. However this is
 142      * corrected in subsequent errata for that RFC.
 143      */
 144     good &= constant_time_lt(threes_in_row, 8);
 145     err = constant_time_select_int(mask | good, err,
 146                                    RSA_R_SSLV3_ROLLBACK_ATTACK);
 147     mask = ~good;
 148
 149     /*
 150      * Skip the zero byte. This is incorrect if we never found a zero-byte
 151      * but in this case we also do not copy the message out.
 152      */
 153     msg_index = zero_index + 1;
 154     mlen = num - msg_index;
 155
 156     /*
 157      * For good measure, do this check in constant time as well.
 158      */
 159     good &= constant_time_ge(tlen, mlen);
 160     err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
 161
 162     /*
 163      * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
 164      * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
 165      * Otherwise leave |to| unchanged.
 166      * Copy the memory back in a way that does not reveal the size of
 167      * the data being copied via a timing side channel. This requires copying
 168      * parts of the buffer multiple times based on the bits set in the real
 169      * length. Clear bits do a non-copy with identical access pattern.
 170      * The loop below has overall complexity of O(N*log(N)).
 171      */
 172     tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
 173                                     num - RSA_PKCS1_PADDING_SIZE, tlen);
 174     for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
 175         mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
 176         for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
 177             em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
 178     }
 179     for (i = 0; i < tlen; i++) {
 180         mask = good & constant_time_lt(i, mlen);
 181         to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
 182     }
 183
 184     OPENSSL_clear_free(em, num);
 185     ERR_raise(ERR_LIB_RSA, err);
 186     err_clear_last_constant_time(1 & good);
 187
 188     return constant_time_select_int(good, mlen, -1);
 189 }