2 * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
3 * WITHOUT WARRANTY OF ANY KIND, either express or implied.
6 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
9 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
10 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
11 * proof for the original OAEP scheme, which EME-OAEP is based on. A new
12 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
13 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
14 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
15 * for the underlying permutation: "partial-one-wayness" instead of
16 * one-wayness. For the RSA function, this is an equivalent notion.
19 #include "internal/constant_time_locl.h"
22 #include "internal/cryptlib.h"
23 #include <openssl/bn.h>
24 #include <openssl/rsa.h>
25 #include <openssl/evp.h>
26 #include <openssl/rand.h>
27 #include <openssl/sha.h>
29 int RSA_padding_add_PKCS1_OAEP(unsigned char *to
, int tlen
,
30 const unsigned char *from
, int flen
,
31 const unsigned char *param
, int plen
)
33 return RSA_padding_add_PKCS1_OAEP_mgf1(to
, tlen
, from
, flen
,
34 param
, plen
, NULL
, NULL
);
37 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to
, int tlen
,
38 const unsigned char *from
, int flen
,
39 const unsigned char *param
, int plen
,
40 const EVP_MD
*md
, const EVP_MD
*mgf1md
)
42 int i
, emlen
= tlen
- 1;
43 unsigned char *db
, *seed
;
44 unsigned char *dbmask
, seedmask
[EVP_MAX_MD_SIZE
];
52 mdlen
= EVP_MD_size(md
);
54 if (flen
> emlen
- 2 * mdlen
- 1) {
55 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
,
56 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE
);
60 if (emlen
< 2 * mdlen
+ 1) {
61 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
,
62 RSA_R_KEY_SIZE_TOO_SMALL
);
70 if (!EVP_Digest((void *)param
, plen
, db
, NULL
, md
, NULL
))
72 memset(db
+ mdlen
, 0, emlen
- flen
- 2 * mdlen
- 1);
73 db
[emlen
- flen
- mdlen
- 1] = 0x01;
74 memcpy(db
+ emlen
- flen
- mdlen
, from
, (unsigned int)flen
);
75 if (RAND_bytes(seed
, mdlen
) <= 0)
79 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
83 dbmask
= OPENSSL_malloc(emlen
- mdlen
);
85 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
, ERR_R_MALLOC_FAILURE
);
89 if (PKCS1_MGF1(dbmask
, emlen
- mdlen
, seed
, mdlen
, mgf1md
) < 0)
91 for (i
= 0; i
< emlen
- mdlen
; i
++)
94 if (PKCS1_MGF1(seedmask
, mdlen
, db
, emlen
- mdlen
, mgf1md
) < 0)
96 for (i
= 0; i
< mdlen
; i
++)
97 seed
[i
] ^= seedmask
[i
];
103 int RSA_padding_check_PKCS1_OAEP(unsigned char *to
, int tlen
,
104 const unsigned char *from
, int flen
, int num
,
105 const unsigned char *param
, int plen
)
107 return RSA_padding_check_PKCS1_OAEP_mgf1(to
, tlen
, from
, flen
, num
,
108 param
, plen
, NULL
, NULL
);
111 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to
, int tlen
,
112 const unsigned char *from
, int flen
,
113 int num
, const unsigned char *param
,
114 int plen
, const EVP_MD
*md
,
115 const EVP_MD
*mgf1md
)
117 int i
, dblen
, mlen
= -1, one_index
= 0, msg_index
;
118 unsigned int good
, found_one_byte
;
119 const unsigned char *maskedseed
, *maskeddb
;
121 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
122 * Y || maskedSeed || maskedDB
124 unsigned char *db
= NULL
, *em
= NULL
, seed
[EVP_MAX_MD_SIZE
],
125 phash
[EVP_MAX_MD_SIZE
];
133 mdlen
= EVP_MD_size(md
);
135 if (tlen
<= 0 || flen
<= 0)
138 * |num| is the length of the modulus; |flen| is the length of the
139 * encoded message. Therefore, for any |from| that was obtained by
140 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
141 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
142 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
143 * This does not leak any side-channel information.
145 if (num
< flen
|| num
< 2 * mdlen
+ 2)
148 dblen
= num
- mdlen
- 1;
149 db
= OPENSSL_malloc(dblen
);
150 em
= OPENSSL_malloc(num
);
151 if (db
== NULL
|| em
== NULL
) {
152 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
, ERR_R_MALLOC_FAILURE
);
157 * Always do this zero-padding copy (even when num == flen) to avoid
158 * leaking that information. The copy still leaks some side-channel
159 * information, but it's impossible to have a fixed memory access
160 * pattern since we can't read out of the bounds of |from|.
162 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
165 memcpy(em
+ num
- flen
, from
, flen
);
168 * The first byte must be zero, however we must not leak if this is
169 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
170 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
172 good
= constant_time_is_zero(em
[0]);
175 maskeddb
= em
+ 1 + mdlen
;
177 if (PKCS1_MGF1(seed
, mdlen
, maskeddb
, dblen
, mgf1md
))
179 for (i
= 0; i
< mdlen
; i
++)
180 seed
[i
] ^= maskedseed
[i
];
182 if (PKCS1_MGF1(db
, dblen
, seed
, mdlen
, mgf1md
))
184 for (i
= 0; i
< dblen
; i
++)
185 db
[i
] ^= maskeddb
[i
];
187 if (!EVP_Digest((void *)param
, plen
, phash
, NULL
, md
, NULL
))
190 good
&= constant_time_is_zero(CRYPTO_memcmp(db
, phash
, mdlen
));
193 for (i
= mdlen
; i
< dblen
; i
++) {
195 * Padding consists of a number of 0-bytes, followed by a 1.
197 unsigned int equals1
= constant_time_eq(db
[i
], 1);
198 unsigned int equals0
= constant_time_is_zero(db
[i
]);
199 one_index
= constant_time_select_int(~found_one_byte
& equals1
,
201 found_one_byte
|= equals1
;
202 good
&= (found_one_byte
| equals0
);
205 good
&= found_one_byte
;
208 * At this point |good| is zero unless the plaintext was valid,
209 * so plaintext-awareness ensures timing side-channels are no longer a
215 msg_index
= one_index
+ 1;
216 mlen
= dblen
- msg_index
;
219 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
, RSA_R_DATA_TOO_LARGE
);
222 memcpy(to
, db
+ msg_index
, mlen
);
228 * To avoid chosen ciphertext attacks, the error message should not
229 * reveal which kind of decoding error happened.
231 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
,
232 RSA_R_OAEP_DECODING_ERROR
);
239 int PKCS1_MGF1(unsigned char *mask
, long len
,
240 const unsigned char *seed
, long seedlen
, const EVP_MD
*dgst
)
243 unsigned char cnt
[4];
244 EVP_MD_CTX
*c
= EVP_MD_CTX_new();
245 unsigned char md
[EVP_MAX_MD_SIZE
];
251 mdlen
= EVP_MD_size(dgst
);
254 for (i
= 0; outlen
< len
; i
++) {
255 cnt
[0] = (unsigned char)((i
>> 24) & 255);
256 cnt
[1] = (unsigned char)((i
>> 16) & 255);
257 cnt
[2] = (unsigned char)((i
>> 8)) & 255;
258 cnt
[3] = (unsigned char)(i
& 255);
259 if (!EVP_DigestInit_ex(c
, dgst
, NULL
)
260 || !EVP_DigestUpdate(c
, seed
, seedlen
)
261 || !EVP_DigestUpdate(c
, cnt
, 4))
263 if (outlen
+ mdlen
<= len
) {
264 if (!EVP_DigestFinal_ex(c
, mask
+ outlen
, NULL
))
268 if (!EVP_DigestFinal_ex(c
, md
, NULL
))
270 memcpy(mask
+ outlen
, md
, len
- outlen
);