1 /* crypto/rsa/rsa_oaep.c */
3 * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
4 * WITHOUT WARRANTY OF ANY KIND, either express or implied.
7 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
10 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
11 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
12 * proof for the original OAEP scheme, which EME-OAEP is based on. A new
13 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
14 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
15 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
16 * for the underlying permutation: "partial-one-wayness" instead of
17 * one-wayness. For the RSA function, this is an equivalent notion.
20 #include "constant_time_locl.h"
24 #include <openssl/bn.h>
25 #include <openssl/rsa.h>
26 #include <openssl/evp.h>
27 #include <openssl/rand.h>
28 #include <openssl/sha.h>
30 int RSA_padding_add_PKCS1_OAEP(unsigned char *to
, int tlen
,
31 const unsigned char *from
, int flen
,
32 const unsigned char *param
, int plen
)
34 return RSA_padding_add_PKCS1_OAEP_mgf1(to
, tlen
, from
, flen
,
35 param
, plen
, NULL
, NULL
);
38 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to
, int tlen
,
39 const unsigned char *from
, int flen
,
40 const unsigned char *param
, int plen
,
41 const EVP_MD
*md
, const EVP_MD
*mgf1md
)
43 int i
, emlen
= tlen
- 1;
44 unsigned char *db
, *seed
;
45 unsigned char *dbmask
, seedmask
[EVP_MAX_MD_SIZE
];
53 mdlen
= EVP_MD_size(md
);
55 if (flen
> emlen
- 2 * mdlen
- 1) {
56 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
,
57 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE
);
61 if (emlen
< 2 * mdlen
+ 1) {
62 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
,
63 RSA_R_KEY_SIZE_TOO_SMALL
);
71 if (!EVP_Digest((void *)param
, plen
, db
, NULL
, md
, NULL
))
73 memset(db
+ mdlen
, 0, emlen
- flen
- 2 * mdlen
- 1);
74 db
[emlen
- flen
- mdlen
- 1] = 0x01;
75 memcpy(db
+ emlen
- flen
- mdlen
, from
, (unsigned int)flen
);
76 if (RAND_bytes(seed
, mdlen
) <= 0)
80 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
84 dbmask
= OPENSSL_malloc(emlen
- mdlen
);
86 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1
, ERR_R_MALLOC_FAILURE
);
90 if (PKCS1_MGF1(dbmask
, emlen
- mdlen
, seed
, mdlen
, mgf1md
) < 0)
92 for (i
= 0; i
< emlen
- mdlen
; i
++)
95 if (PKCS1_MGF1(seedmask
, mdlen
, db
, emlen
- mdlen
, mgf1md
) < 0)
97 for (i
= 0; i
< mdlen
; i
++)
98 seed
[i
] ^= seedmask
[i
];
100 OPENSSL_free(dbmask
);
104 int RSA_padding_check_PKCS1_OAEP(unsigned char *to
, int tlen
,
105 const unsigned char *from
, int flen
, int num
,
106 const unsigned char *param
, int plen
)
108 return RSA_padding_check_PKCS1_OAEP_mgf1(to
, tlen
, from
, flen
, num
,
109 param
, plen
, NULL
, NULL
);
112 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to
, int tlen
,
113 const unsigned char *from
, int flen
,
114 int num
, const unsigned char *param
,
115 int plen
, const EVP_MD
*md
,
116 const EVP_MD
*mgf1md
)
118 int i
, dblen
, mlen
= -1, one_index
= 0, msg_index
;
119 unsigned int good
, found_one_byte
;
120 const unsigned char *maskedseed
, *maskeddb
;
122 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
123 * Y || maskedSeed || maskedDB
125 unsigned char *db
= NULL
, *em
= NULL
, seed
[EVP_MAX_MD_SIZE
],
126 phash
[EVP_MAX_MD_SIZE
];
134 mdlen
= EVP_MD_size(md
);
136 if (tlen
<= 0 || flen
<= 0)
139 * |num| is the length of the modulus; |flen| is the length of the
140 * encoded message. Therefore, for any |from| that was obtained by
141 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
142 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
143 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
144 * This does not leak any side-channel information.
146 if (num
< flen
|| num
< 2 * mdlen
+ 2)
149 dblen
= num
- mdlen
- 1;
150 db
= OPENSSL_malloc(dblen
);
151 em
= OPENSSL_malloc(num
);
152 if (db
== NULL
|| em
== NULL
) {
153 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
, ERR_R_MALLOC_FAILURE
);
158 * Always do this zero-padding copy (even when num == flen) to avoid
159 * leaking that information. The copy still leaks some side-channel
160 * information, but it's impossible to have a fixed memory access
161 * pattern since we can't read out of the bounds of |from|.
163 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
166 memcpy(em
+ num
- flen
, from
, flen
);
169 * The first byte must be zero, however we must not leak if this is
170 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
171 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
173 good
= constant_time_is_zero(em
[0]);
176 maskeddb
= em
+ 1 + mdlen
;
178 if (PKCS1_MGF1(seed
, mdlen
, maskeddb
, dblen
, mgf1md
))
180 for (i
= 0; i
< mdlen
; i
++)
181 seed
[i
] ^= maskedseed
[i
];
183 if (PKCS1_MGF1(db
, dblen
, seed
, mdlen
, mgf1md
))
185 for (i
= 0; i
< dblen
; i
++)
186 db
[i
] ^= maskeddb
[i
];
188 if (!EVP_Digest((void *)param
, plen
, phash
, NULL
, md
, NULL
))
191 good
&= constant_time_is_zero(CRYPTO_memcmp(db
, phash
, mdlen
));
194 for (i
= mdlen
; i
< dblen
; i
++) {
196 * Padding consists of a number of 0-bytes, followed by a 1.
198 unsigned int equals1
= constant_time_eq(db
[i
], 1);
199 unsigned int equals0
= constant_time_is_zero(db
[i
]);
200 one_index
= constant_time_select_int(~found_one_byte
& equals1
,
202 found_one_byte
|= equals1
;
203 good
&= (found_one_byte
| equals0
);
206 good
&= found_one_byte
;
209 * At this point |good| is zero unless the plaintext was valid,
210 * so plaintext-awareness ensures timing side-channels are no longer a
216 msg_index
= one_index
+ 1;
217 mlen
= dblen
- msg_index
;
220 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
, RSA_R_DATA_TOO_LARGE
);
223 memcpy(to
, db
+ msg_index
, mlen
);
229 * To avoid chosen ciphertext attacks, the error message should not
230 * reveal which kind of decoding error happened.
232 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1
,
233 RSA_R_OAEP_DECODING_ERROR
);
242 int PKCS1_MGF1(unsigned char *mask
, long len
,
243 const unsigned char *seed
, long seedlen
, const EVP_MD
*dgst
)
246 unsigned char cnt
[4];
248 unsigned char md
[EVP_MAX_MD_SIZE
];
253 mdlen
= M_EVP_MD_size(dgst
);
256 for (i
= 0; outlen
< len
; i
++) {
257 cnt
[0] = (unsigned char)((i
>> 24) & 255);
258 cnt
[1] = (unsigned char)((i
>> 16) & 255);
259 cnt
[2] = (unsigned char)((i
>> 8)) & 255;
260 cnt
[3] = (unsigned char)(i
& 255);
261 if (!EVP_DigestInit_ex(&c
, dgst
, NULL
)
262 || !EVP_DigestUpdate(&c
, seed
, seedlen
)
263 || !EVP_DigestUpdate(&c
, cnt
, 4))
265 if (outlen
+ mdlen
<= len
) {
266 if (!EVP_DigestFinal_ex(&c
, mask
+ outlen
, NULL
))
270 if (!EVP_DigestFinal_ex(&c
, md
, NULL
))
272 memcpy(mask
+ outlen
, md
, len
- outlen
);
278 EVP_MD_CTX_cleanup(&c
);