2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
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
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 * Move the result in-place by |num|-11-|mlen| bytes to the left.
230 * Then if |good| move |mlen| bytes from |em|+11 to |to|.
231 * Otherwise leave |to| unchanged.
232 * Copy the memory back in a way that does not reveal the size of
233 * the data being copied via a timing side channel. This requires copying
234 * parts of the buffer multiple times based on the bits set in the real
235 * length. Clear bits do a non-copy with identical access pattern.
236 * The loop below has overall complexity of O(N*log(N)).
238 tlen
= constant_time_select_int(constant_time_lt(num
- 11, tlen
),
240 for (msg_index
= 1; msg_index
< num
- 11; msg_index
<<= 1) {
241 mask
= ~constant_time_eq(msg_index
& (num
- 11 - mlen
), 0);
242 for (i
= 11; i
< num
- msg_index
; i
++)
243 em
[i
] = constant_time_select_8(mask
, em
[i
+ msg_index
], em
[i
]);
245 for (i
= 0; i
< tlen
; i
++) {
246 mask
= good
& constant_time_lt(i
, mlen
);
247 to
[i
] = constant_time_select_8(mask
, em
[i
+ 11], 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);