1 /* 2 * Copyright 1995-2016 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 "internal/constant_time_locl.h" 11 12 #include <stdio.h> 13 #include "internal/cryptlib.h" 14 #include <openssl/bn.h> 15 #include <openssl/rsa.h> 16 #include <openssl/rand.h> 17 18 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen, 19 const unsigned char *from, int flen) 20 { 21 int j; 22 unsigned char *p; 23 24 if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) { 25 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1, 26 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 27 return (0); 28 } 29 30 p = (unsigned char *)to; 31 32 *(p++) = 0; 33 *(p++) = 1; /* Private Key BT (Block Type) */ 34 35 /* pad out with 0xff data */ 36 j = tlen - 3 - flen; 37 memset(p, 0xff, j); 38 p += j; 39 *(p++) = '\0'; 40 memcpy(p, from, (unsigned int)flen); 41 return (1); 42 } 43 44 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen, 45 const unsigned char *from, int flen, 46 int num) 47 { 48 int i, j; 49 const unsigned char *p; 50 51 p = from; 52 53 /* 54 * The format is 55 * 00 || 01 || PS || 00 || D 56 * PS - padding string, at least 8 bytes of FF 57 * D - data. 58 */ 59 60 if (num < 11) 61 return -1; 62 63 /* Accept inputs with and without the leading 0-byte. */ 64 if (num == flen) { 65 if ((*p++) != 0x00) { 66 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, 67 RSA_R_INVALID_PADDING); 68 return -1; 69 } 70 flen--; 71 } 72 73 if ((num != (flen + 1)) || (*(p++) != 0x01)) { 74 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, 75 RSA_R_BLOCK_TYPE_IS_NOT_01); 76 return (-1); 77 } 78 79 /* scan over padding data */ 80 j = flen - 1; /* one for type. */ 81 for (i = 0; i < j; i++) { 82 if (*p != 0xff) { /* should decrypt to 0xff */ 83 if (*p == 0) { 84 p++; 85 break; 86 } else { 87 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, 88 RSA_R_BAD_FIXED_HEADER_DECRYPT); 89 return (-1); 90 } 91 } 92 p++; 93 } 94 95 if (i == j) { 96 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, 97 RSA_R_NULL_BEFORE_BLOCK_MISSING); 98 return (-1); 99 } 100 101 if (i < 8) { 102 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, 103 RSA_R_BAD_PAD_BYTE_COUNT); 104 return (-1); 105 } 106 i++; /* Skip over the '\0' */ 107 j -= i; 108 if (j > tlen) { 109 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE); 110 return (-1); 111 } 112 memcpy(to, p, (unsigned int)j); 113 114 return (j); 115 } 116 117 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen, 118 const unsigned char *from, int flen) 119 { 120 int i, j; 121 unsigned char *p; 122 123 if (flen > (tlen - 11)) { 124 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2, 125 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 126 return (0); 127 } 128 129 p = (unsigned char *)to; 130 131 *(p++) = 0; 132 *(p++) = 2; /* Public Key BT (Block Type) */ 133 134 /* pad out with non-zero random data */ 135 j = tlen - 3 - flen; 136 137 if (RAND_bytes(p, j) <= 0) 138 return (0); 139 for (i = 0; i < j; i++) { 140 if (*p == '\0') 141 do { 142 if (RAND_bytes(p, 1) <= 0) 143 return (0); 144 } while (*p == '\0'); 145 p++; 146 } 147 148 *(p++) = '\0'; 149 150 memcpy(p, from, (unsigned int)flen); 151 return (1); 152 } 153 154 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen, 155 const unsigned char *from, int flen, 156 int num) 157 { 158 int i; 159 /* |em| is the encoded message, zero-padded to exactly |num| bytes */ 160 unsigned char *em = NULL; 161 unsigned int good, found_zero_byte; 162 int zero_index = 0, msg_index, mlen = -1; 163 164 if (tlen < 0 || flen < 0) 165 return -1; 166 167 /* 168 * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard", 169 * section 7.2.2. 170 */ 171 172 if (flen > num) 173 goto err; 174 175 if (num < 11) 176 goto err; 177 178 em = OPENSSL_zalloc(num); 179 if (em == NULL) { 180 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE); 181 return -1; 182 } 183 /* 184 * Always do this zero-padding copy (even when num == flen) to avoid 185 * leaking that information. The copy still leaks some side-channel 186 * information, but it's impossible to have a fixed memory access 187 * pattern since we can't read out of the bounds of |from|. 188 * 189 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL. 190 */ 191 memcpy(em + num - flen, from, flen); 192 193 good = constant_time_is_zero(em[0]); 194 good &= constant_time_eq(em[1], 2); 195 196 found_zero_byte = 0; 197 for (i = 2; i < num; i++) { 198 unsigned int equals0 = constant_time_is_zero(em[i]); 199 zero_index = 200 constant_time_select_int(~found_zero_byte & equals0, i, 201 zero_index); 202 found_zero_byte |= equals0; 203 } 204 205 /* 206 * PS must be at least 8 bytes long, and it starts two bytes into |em|. 207 * If we never found a 0-byte, then |zero_index| is 0 and the check 208 * also fails. 209 */ 210 good &= constant_time_ge((unsigned int)(zero_index), 2 + 8); 211 212 /* 213 * Skip the zero byte. This is incorrect if we never found a zero-byte 214 * but in this case we also do not copy the message out. 215 */ 216 msg_index = zero_index + 1; 217 mlen = num - msg_index; 218 219 /* 220 * For good measure, do this check in constant time as well; it could 221 * leak something if |tlen| was assuming valid padding. 222 */ 223 good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen)); 224 225 /* 226 * We can't continue in constant-time because we need to copy the result 227 * and we cannot fake its length. This unavoidably leaks timing 228 * information at the API boundary. 229 */ 230 if (!good) { 231 mlen = -1; 232 goto err; 233 } 234 235 memcpy(to, em + msg_index, mlen); 236 237 err: 238 OPENSSL_clear_free(em, num); 239 if (mlen == -1) 240 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, 241 RSA_R_PKCS_DECODING_ERROR); 242 return mlen; 243 } 244