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"
22 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
24 # include "cryptlib.h"
25 # include <openssl/bn.h>
26 # include <openssl/rsa.h>
27 # include <openssl/evp.h>
28 # include <openssl/rand.h>
29 # include <openssl/sha.h>
31 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
32 const unsigned char *from, int flen,
33 const unsigned char *param, int plen)
35 return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
36 param, plen, NULL, NULL);
39 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
40 const unsigned char *from, int flen,
41 const unsigned char *param, int plen,
42 const EVP_MD *md, const EVP_MD *mgf1md)
44 int i, emlen = tlen - 1;
45 unsigned char *db, *seed;
46 unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
54 mdlen = EVP_MD_size(md);
56 if (flen > emlen - 2 * mdlen - 1) {
57 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
58 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
62 if (emlen < 2 * mdlen + 1) {
63 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
64 RSA_R_KEY_SIZE_TOO_SMALL);
72 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
74 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
75 db[emlen - flen - mdlen - 1] = 0x01;
76 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
77 if (RAND_bytes(seed, mdlen) <= 0)
81 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
85 dbmask = OPENSSL_malloc(emlen - mdlen);
87 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
91 if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
93 for (i = 0; i < emlen - mdlen; i++)
96 if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
98 for (i = 0; i < mdlen; i++)
99 seed[i] ^= seedmask[i];
101 OPENSSL_free(dbmask);
105 OPENSSL_free(dbmask);
109 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
110 const unsigned char *from, int flen, int num,
111 const unsigned char *param, int plen)
113 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
114 param, plen, NULL, NULL);
117 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
118 const unsigned char *from, int flen,
119 int num, const unsigned char *param,
120 int plen, const EVP_MD *md,
121 const EVP_MD *mgf1md)
123 int i, dblen, mlen = -1, one_index = 0, msg_index;
124 unsigned int good, found_one_byte;
125 const unsigned char *maskedseed, *maskeddb;
127 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
128 * Y || maskedSeed || maskedDB
130 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
131 phash[EVP_MAX_MD_SIZE];
139 mdlen = EVP_MD_size(md);
141 if (tlen <= 0 || flen <= 0)
144 * |num| is the length of the modulus; |flen| is the length of the
145 * encoded message. Therefore, for any |from| that was obtained by
146 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
147 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
148 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
149 * This does not leak any side-channel information.
151 if (num < flen || num < 2 * mdlen + 2)
154 dblen = num - mdlen - 1;
155 db = OPENSSL_malloc(dblen);
156 em = OPENSSL_malloc(num);
157 if (db == NULL || em == NULL) {
158 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
163 * Always do this zero-padding copy (even when num == flen) to avoid
164 * leaking that information. The copy still leaks some side-channel
165 * information, but it's impossible to have a fixed memory access
166 * pattern since we can't read out of the bounds of |from|.
168 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
171 memcpy(em + num - flen, from, flen);
174 * The first byte must be zero, however we must not leak if this is
175 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
176 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
178 good = constant_time_is_zero(em[0]);
181 maskeddb = em + 1 + mdlen;
183 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
185 for (i = 0; i < mdlen; i++)
186 seed[i] ^= maskedseed[i];
188 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
190 for (i = 0; i < dblen; i++)
191 db[i] ^= maskeddb[i];
193 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
196 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
199 for (i = mdlen; i < dblen; i++) {
201 * Padding consists of a number of 0-bytes, followed by a 1.
203 unsigned int equals1 = constant_time_eq(db[i], 1);
204 unsigned int equals0 = constant_time_is_zero(db[i]);
205 one_index = constant_time_select_int(~found_one_byte & equals1,
207 found_one_byte |= equals1;
208 good &= (found_one_byte | equals0);
211 good &= found_one_byte;
214 * At this point |good| is zero unless the plaintext was valid,
215 * so plaintext-awareness ensures timing side-channels are no longer a
221 msg_index = one_index + 1;
222 mlen = dblen - msg_index;
225 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
228 memcpy(to, db + msg_index, mlen);
234 * To avoid chosen ciphertext attacks, the error message should not
235 * reveal which kind of decoding error happened.
237 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
238 RSA_R_OAEP_DECODING_ERROR);
241 OPENSSL_cleanse(db, dblen);
245 OPENSSL_cleanse(em, num);
251 int PKCS1_MGF1(unsigned char *mask, long len,
252 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
255 unsigned char cnt[4];
257 unsigned char md[EVP_MAX_MD_SIZE];
262 mdlen = EVP_MD_size(dgst);
265 for (i = 0; outlen < len; i++) {
266 cnt[0] = (unsigned char)((i >> 24) & 255);
267 cnt[1] = (unsigned char)((i >> 16) & 255);
268 cnt[2] = (unsigned char)((i >> 8)) & 255;
269 cnt[3] = (unsigned char)(i & 255);
270 if (!EVP_DigestInit_ex(&c, dgst, NULL)
271 || !EVP_DigestUpdate(&c, seed, seedlen)
272 || !EVP_DigestUpdate(&c, cnt, 4))
274 if (outlen + mdlen <= len) {
275 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
279 if (!EVP_DigestFinal_ex(&c, md, NULL))
281 memcpy(mask + outlen, md, len - outlen);
287 EVP_MD_CTX_cleanup(&c);