1 /* 2 * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved. 3 * 4 * Licensed under the OpenSSL license (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 - RSA_PKCS1_PADDING_SIZE)) { 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 (tlen <= 0 || flen <= 0) 71 return -1; 72 73 if (flen > num || num < RSA_PKCS1_PADDING_SIZE) { 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 /* 126 * Reject if nul delimiter is preceded by 8 consecutive 0x03 bytes. Note 127 * that RFC5246 incorrectly states this the other way around, i.e. reject 128 * if it is not preceded by 8 consecutive 0x03 bytes. However this is 129 * corrected in subsequent errata for that RFC. 130 */ 131 good &= constant_time_lt(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 } 177