Line data Source code
1 : /* crypto/rsa/rsa_oaep.c */
2 : /*
3 : * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
4 : * WITHOUT WARRANTY OF ANY KIND, either express or implied.
5 : */
6 :
7 : /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
8 :
9 : /*
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.
18 : */
19 :
20 : #include "constant_time_locl.h"
21 :
22 : #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
23 : # include <stdio.h>
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>
30 :
31 0 : 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)
34 : {
35 0 : return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
36 : param, plen, NULL, NULL);
37 : }
38 :
39 0 : 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)
43 : {
44 0 : int i, emlen = tlen - 1;
45 : unsigned char *db, *seed;
46 : unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
47 : int mdlen;
48 :
49 0 : if (md == NULL)
50 0 : md = EVP_sha1();
51 0 : if (mgf1md == NULL)
52 : mgf1md = md;
53 :
54 0 : mdlen = EVP_MD_size(md);
55 :
56 0 : if (flen > emlen - 2 * mdlen - 1) {
57 0 : RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
58 : RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
59 0 : return 0;
60 : }
61 :
62 0 : if (emlen < 2 * mdlen + 1) {
63 0 : RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
64 : RSA_R_KEY_SIZE_TOO_SMALL);
65 0 : return 0;
66 : }
67 :
68 0 : to[0] = 0;
69 0 : seed = to + 1;
70 0 : db = to + mdlen + 1;
71 :
72 0 : if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
73 : return 0;
74 0 : memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
75 0 : db[emlen - flen - mdlen - 1] = 0x01;
76 0 : memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
77 0 : if (RAND_bytes(seed, mdlen) <= 0)
78 : return 0;
79 : # ifdef PKCS_TESTVECT
80 : memcpy(seed,
81 : "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
82 : 20);
83 : # endif
84 :
85 0 : dbmask = OPENSSL_malloc(emlen - mdlen);
86 0 : if (dbmask == NULL) {
87 0 : RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
88 0 : return 0;
89 : }
90 :
91 0 : if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
92 : return 0;
93 0 : for (i = 0; i < emlen - mdlen; i++)
94 0 : db[i] ^= dbmask[i];
95 :
96 0 : if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
97 : return 0;
98 0 : for (i = 0; i < mdlen; i++)
99 0 : seed[i] ^= seedmask[i];
100 :
101 0 : OPENSSL_free(dbmask);
102 0 : return 1;
103 : }
104 :
105 0 : int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
106 : const unsigned char *from, int flen, int num,
107 : const unsigned char *param, int plen)
108 : {
109 0 : return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
110 : param, plen, NULL, NULL);
111 : }
112 :
113 0 : int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
114 : const unsigned char *from, int flen,
115 : int num, const unsigned char *param,
116 : int plen, const EVP_MD *md,
117 : const EVP_MD *mgf1md)
118 : {
119 : int i, dblen, mlen = -1, one_index = 0, msg_index;
120 : unsigned int good, found_one_byte;
121 : const unsigned char *maskedseed, *maskeddb;
122 : /*
123 : * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
124 : * Y || maskedSeed || maskedDB
125 : */
126 : unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
127 : phash[EVP_MAX_MD_SIZE];
128 : int mdlen;
129 :
130 0 : if (md == NULL)
131 0 : md = EVP_sha1();
132 0 : if (mgf1md == NULL)
133 : mgf1md = md;
134 :
135 0 : mdlen = EVP_MD_size(md);
136 :
137 0 : if (tlen <= 0 || flen <= 0)
138 : return -1;
139 : /*
140 : * |num| is the length of the modulus; |flen| is the length of the
141 : * encoded message. Therefore, for any |from| that was obtained by
142 : * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
143 : * num < 2 * mdlen + 2 must hold for the modulus irrespective of
144 : * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
145 : * This does not leak any side-channel information.
146 : */
147 0 : if (num < flen || num < 2 * mdlen + 2)
148 : goto decoding_err;
149 :
150 0 : dblen = num - mdlen - 1;
151 0 : db = OPENSSL_malloc(dblen);
152 0 : em = OPENSSL_malloc(num);
153 0 : if (db == NULL || em == NULL) {
154 0 : RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
155 0 : goto cleanup;
156 : }
157 :
158 : /*
159 : * Always do this zero-padding copy (even when num == flen) to avoid
160 : * leaking that information. The copy still leaks some side-channel
161 : * information, but it's impossible to have a fixed memory access
162 : * pattern since we can't read out of the bounds of |from|.
163 : *
164 : * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
165 : */
166 0 : memset(em, 0, num);
167 0 : memcpy(em + num - flen, from, flen);
168 :
169 : /*
170 : * The first byte must be zero, however we must not leak if this is
171 : * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
172 : * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
173 : */
174 0 : good = constant_time_is_zero(em[0]);
175 :
176 0 : maskedseed = em + 1;
177 0 : maskeddb = em + 1 + mdlen;
178 :
179 0 : if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
180 : goto cleanup;
181 0 : for (i = 0; i < mdlen; i++)
182 0 : seed[i] ^= maskedseed[i];
183 :
184 0 : if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
185 : goto cleanup;
186 0 : for (i = 0; i < dblen; i++)
187 0 : db[i] ^= maskeddb[i];
188 :
189 0 : if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
190 : goto cleanup;
191 :
192 0 : good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
193 :
194 : found_one_byte = 0;
195 0 : for (i = mdlen; i < dblen; i++) {
196 : /*
197 : * Padding consists of a number of 0-bytes, followed by a 1.
198 : */
199 0 : unsigned int equals1 = constant_time_eq(db[i], 1);
200 0 : unsigned int equals0 = constant_time_is_zero(db[i]);
201 0 : one_index = constant_time_select_int(~found_one_byte & equals1,
202 : i, one_index);
203 0 : found_one_byte |= equals1;
204 0 : good &= (found_one_byte | equals0);
205 : }
206 :
207 0 : good &= found_one_byte;
208 :
209 : /*
210 : * At this point |good| is zero unless the plaintext was valid,
211 : * so plaintext-awareness ensures timing side-channels are no longer a
212 : * concern.
213 : */
214 0 : if (!good)
215 : goto decoding_err;
216 :
217 0 : msg_index = one_index + 1;
218 0 : mlen = dblen - msg_index;
219 :
220 0 : if (tlen < mlen) {
221 0 : RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
222 : mlen = -1;
223 : } else {
224 0 : memcpy(to, db + msg_index, mlen);
225 : goto cleanup;
226 : }
227 :
228 : decoding_err:
229 : /*
230 : * To avoid chosen ciphertext attacks, the error message should not
231 : * reveal which kind of decoding error happened.
232 : */
233 0 : RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
234 : RSA_R_OAEP_DECODING_ERROR);
235 : cleanup:
236 0 : if (db != NULL)
237 0 : OPENSSL_free(db);
238 0 : if (em != NULL)
239 0 : OPENSSL_free(em);
240 0 : return mlen;
241 : }
242 :
243 0 : int PKCS1_MGF1(unsigned char *mask, long len,
244 : const unsigned char *seed, long seedlen, const EVP_MD *dgst)
245 : {
246 : long i, outlen = 0;
247 : unsigned char cnt[4];
248 : EVP_MD_CTX c;
249 : unsigned char md[EVP_MAX_MD_SIZE];
250 : int mdlen;
251 : int rv = -1;
252 :
253 0 : EVP_MD_CTX_init(&c);
254 0 : mdlen = EVP_MD_size(dgst);
255 0 : if (mdlen < 0)
256 : goto err;
257 0 : for (i = 0; outlen < len; i++) {
258 0 : cnt[0] = (unsigned char)((i >> 24) & 255);
259 0 : cnt[1] = (unsigned char)((i >> 16) & 255);
260 0 : cnt[2] = (unsigned char)((i >> 8)) & 255;
261 0 : cnt[3] = (unsigned char)(i & 255);
262 0 : if (!EVP_DigestInit_ex(&c, dgst, NULL)
263 0 : || !EVP_DigestUpdate(&c, seed, seedlen)
264 0 : || !EVP_DigestUpdate(&c, cnt, 4))
265 : goto err;
266 0 : if (outlen + mdlen <= len) {
267 0 : if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
268 : goto err;
269 : outlen += mdlen;
270 : } else {
271 0 : if (!EVP_DigestFinal_ex(&c, md, NULL))
272 : goto err;
273 0 : memcpy(mask + outlen, md, len - outlen);
274 : outlen = len;
275 : }
276 : }
277 : rv = 0;
278 : err:
279 0 : EVP_MD_CTX_cleanup(&c);
280 0 : return rv;
281 : }
282 :
283 : #endif
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