2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
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
10 #include "internal/constant_time_locl.h"
13 #include "internal/cryptlib.h"
14 #include <openssl/bn.h>
15 #include <openssl/rsa.h>
16 #include <openssl/rand.h>
18 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
19 const unsigned char *from, int flen)
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);
30 p = (unsigned char *)to;
33 *(p++) = 1; /* Private Key BT (Block Type) */
35 /* pad out with 0xff data */
40 memcpy(p, from, (unsigned int)flen);
44 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
45 const unsigned char *from, int flen,
49 const unsigned char *p;
55 * 00 || 01 || PS || 00 || D
56 * PS - padding string, at least 8 bytes of FF
63 /* Accept inputs with and without the leading 0-byte. */
66 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
67 RSA_R_INVALID_PADDING);
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);
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 */
87 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
88 RSA_R_BAD_FIXED_HEADER_DECRYPT);
96 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
97 RSA_R_NULL_BEFORE_BLOCK_MISSING);
102 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
103 RSA_R_BAD_PAD_BYTE_COUNT);
106 i++; /* Skip over the '\0' */
109 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
112 memcpy(to, p, (unsigned int)j);
117 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
118 const unsigned char *from, int flen)
123 if (flen > (tlen - 11)) {
124 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2,
125 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
129 p = (unsigned char *)to;
132 *(p++) = 2; /* Public Key BT (Block Type) */
134 /* pad out with non-zero random data */
137 if (RAND_bytes(p, j) <= 0)
139 for (i = 0; i < j; i++) {
142 if (RAND_bytes(p, 1) <= 0)
144 } while (*p == '\0');
150 memcpy(p, from, (unsigned int)flen);
154 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
155 const unsigned char *from, int flen,
159 /* |em| is the encoded message, zero-padded to exactly |num| bytes */
160 unsigned char *em = NULL;
161 unsigned int good, found_zero_byte, mask;
162 int zero_index = 0, msg_index, mlen = -1;
164 if (tlen <= 0 || flen <= 0)
168 * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
172 if (flen > num || num < 11) {
173 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
174 RSA_R_PKCS_DECODING_ERROR);
178 em = OPENSSL_malloc(num);
180 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
184 * Caller is encouraged to pass zero-padded message created with
185 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
186 * bounds, it's impossible to have an invariant memory access pattern
187 * in case |from| was not zero-padded in advance.
189 for (from += flen, em += num, i = 0; i < num; i++) {
190 mask = ~constant_time_is_zero(flen);
193 *--em = *from & mask;
196 good = constant_time_is_zero(em[0]);
197 good &= constant_time_eq(em[1], 2);
199 /* scan over padding data */
201 for (i = 2; i < num; i++) {
202 unsigned int equals0 = constant_time_is_zero(em[i]);
204 zero_index = constant_time_select_int(~found_zero_byte & equals0,
206 found_zero_byte |= equals0;
210 * PS must be at least 8 bytes long, and it starts two bytes into |em|.
211 * If we never found a 0-byte, then |zero_index| is 0 and the check
214 good &= constant_time_ge(zero_index, 2 + 8);
217 * Skip the zero byte. This is incorrect if we never found a zero-byte
218 * but in this case we also do not copy the message out.
220 msg_index = zero_index + 1;
221 mlen = num - msg_index;
224 * For good measure, do this check in constant time as well.
226 good &= constant_time_ge(tlen, mlen);
229 * Even though we can't fake result's length, we can pretend copying
230 * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
231 * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
232 * where |mlen'| is "saturated" |mlen| value. Deducing information
233 * about failure or |mlen| would take attacker's ability to observe
234 * memory access pattern with byte granularity *as it occurs*. It
235 * should be noted that failure is indistinguishable from normal
236 * operation if |tlen| is fixed by protocol.
238 tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
240 msg_index = constant_time_select_int(good, msg_index, num - tlen);
241 mlen = num - msg_index;
242 for (mask = good, i = 0; i < tlen; i++) {
243 unsigned int equals = constant_time_eq(msg_index, num);
245 msg_index -= tlen & equals; /* rewind at EOF */
246 mask &= ~equals; /* mask = 0 at EOF */
247 to[i] = constant_time_select_8(mask, em[msg_index++], to[i]);
250 OPENSSL_clear_free(em, num);
251 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
252 err_clear_last_constant_time(1 & good);
254 return constant_time_select_int(good, mlen, -1);