1 | /* |
2 | * Copyright 1999-2019 The OpenSSL Project Authors. All Rights Reserved. |
3 | * |
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 |
8 | */ |
9 | |
10 | /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ |
11 | |
12 | /* |
13 | * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL: |
14 | * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security |
15 | * proof for the original OAEP scheme, which EME-OAEP is based on. A new |
16 | * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern, |
17 | * "RSA-OEAP is Still Alive!", Dec. 2000, <URL: |
18 | * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements |
19 | * for the underlying permutation: "partial-one-wayness" instead of |
20 | * one-wayness. For the RSA function, this is an equivalent notion. |
21 | */ |
22 | |
23 | #include "internal/constant_time.h" |
24 | |
25 | #include <stdio.h> |
26 | #include "internal/cryptlib.h" |
27 | #include <openssl/bn.h> |
28 | #include <openssl/evp.h> |
29 | #include <openssl/rand.h> |
30 | #include <openssl/sha.h> |
31 | #include "rsa_local.h" |
32 | |
33 | int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, |
34 | const unsigned char *from, int flen, |
35 | const unsigned char *param, int plen) |
36 | { |
37 | return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen, |
38 | param, plen, NULL, NULL); |
39 | } |
40 | |
41 | /* |
42 | * Perform ihe padding as per NIST 800-56B 7.2.2.3 |
43 | * from (K) is the key material. |
44 | * param (A) is the additional input. |
45 | * Step numbers are included here but not in the constant time inverse below |
46 | * to avoid complicating an already difficult enough function. |
47 | */ |
48 | int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, |
49 | const unsigned char *from, int flen, |
50 | const unsigned char *param, int plen, |
51 | const EVP_MD *md, const EVP_MD *mgf1md) |
52 | { |
53 | int rv = 0; |
54 | int i, emlen = tlen - 1; |
55 | unsigned char *db, *seed; |
56 | unsigned char *dbmask = NULL; |
57 | unsigned char seedmask[EVP_MAX_MD_SIZE]; |
58 | int mdlen, dbmask_len = 0; |
59 | |
60 | if (md == NULL) |
61 | md = EVP_sha1(); |
62 | if (mgf1md == NULL) |
63 | mgf1md = md; |
64 | |
65 | mdlen = EVP_MD_size(md); |
66 | |
67 | /* step 2b: check KLen > nLen - 2 HLen - 2 */ |
68 | if (flen > emlen - 2 * mdlen - 1) { |
69 | RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, |
70 | RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); |
71 | return 0; |
72 | } |
73 | |
74 | if (emlen < 2 * mdlen + 1) { |
75 | RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, |
76 | RSA_R_KEY_SIZE_TOO_SMALL); |
77 | return 0; |
78 | } |
79 | |
80 | /* step 3i: EM = 00000000 || maskedMGF || maskedDB */ |
81 | to[0] = 0; |
82 | seed = to + 1; |
83 | db = to + mdlen + 1; |
84 | |
85 | /* step 3a: hash the additional input */ |
86 | if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL)) |
87 | goto err; |
88 | /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */ |
89 | memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1); |
90 | /* step 3c: DB = HA || PS || 00000001 || K */ |
91 | db[emlen - flen - mdlen - 1] = 0x01; |
92 | memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen); |
93 | /* step 3d: generate random byte string */ |
94 | if (RAND_bytes(seed, mdlen) <= 0) |
95 | goto err; |
96 | |
97 | dbmask_len = emlen - mdlen; |
98 | dbmask = OPENSSL_malloc(dbmask_len); |
99 | if (dbmask == NULL) { |
100 | RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE); |
101 | goto err; |
102 | } |
103 | |
104 | /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */ |
105 | if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0) |
106 | goto err; |
107 | /* step 3f: maskedDB = DB XOR dbMask */ |
108 | for (i = 0; i < dbmask_len; i++) |
109 | db[i] ^= dbmask[i]; |
110 | |
111 | /* step 3g: mgfSeed = MGF(maskedDB, HLen) */ |
112 | if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0) |
113 | goto err; |
114 | /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */ |
115 | for (i = 0; i < mdlen; i++) |
116 | seed[i] ^= seedmask[i]; |
117 | rv = 1; |
118 | |
119 | err: |
120 | OPENSSL_cleanse(seedmask, sizeof(seedmask)); |
121 | OPENSSL_clear_free(dbmask, dbmask_len); |
122 | return rv; |
123 | } |
124 | |
125 | int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, |
126 | const unsigned char *from, int flen, int num, |
127 | const unsigned char *param, int plen) |
128 | { |
129 | return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num, |
130 | param, plen, NULL, NULL); |
131 | } |
132 | |
133 | int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, |
134 | const unsigned char *from, int flen, |
135 | int num, const unsigned char *param, |
136 | int plen, const EVP_MD *md, |
137 | const EVP_MD *mgf1md) |
138 | { |
139 | int i, dblen = 0, mlen = -1, one_index = 0, msg_index; |
140 | unsigned int good = 0, found_one_byte, mask; |
141 | const unsigned char *maskedseed, *maskeddb; |
142 | /* |
143 | * |em| is the encoded message, zero-padded to exactly |num| bytes: em = |
144 | * Y || maskedSeed || maskedDB |
145 | */ |
146 | unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], |
147 | phash[EVP_MAX_MD_SIZE]; |
148 | int mdlen; |
149 | |
150 | if (md == NULL) |
151 | md = EVP_sha1(); |
152 | if (mgf1md == NULL) |
153 | mgf1md = md; |
154 | |
155 | mdlen = EVP_MD_size(md); |
156 | |
157 | if (tlen <= 0 || flen <= 0) |
158 | return -1; |
159 | /* |
160 | * |num| is the length of the modulus; |flen| is the length of the |
161 | * encoded message. Therefore, for any |from| that was obtained by |
162 | * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, |
163 | * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of |
164 | * the ciphertext, see PKCS #1 v2.2, section 7.1.2. |
165 | * This does not leak any side-channel information. |
166 | */ |
167 | if (num < flen || num < 2 * mdlen + 2) { |
168 | RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, |
169 | RSA_R_OAEP_DECODING_ERROR); |
170 | return -1; |
171 | } |
172 | |
173 | dblen = num - mdlen - 1; |
174 | db = OPENSSL_malloc(dblen); |
175 | if (db == NULL) { |
176 | RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE); |
177 | goto cleanup; |
178 | } |
179 | |
180 | em = OPENSSL_malloc(num); |
181 | if (em == NULL) { |
182 | RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, |
183 | ERR_R_MALLOC_FAILURE); |
184 | goto cleanup; |
185 | } |
186 | |
187 | /* |
188 | * Caller is encouraged to pass zero-padded message created with |
189 | * BN_bn2binpad. Trouble is that since we can't read out of |from|'s |
190 | * bounds, it's impossible to have an invariant memory access pattern |
191 | * in case |from| was not zero-padded in advance. |
192 | */ |
193 | for (from += flen, em += num, i = 0; i < num; i++) { |
194 | mask = ~constant_time_is_zero(flen); |
195 | flen -= 1 & mask; |
196 | from -= 1 & mask; |
197 | *--em = *from & mask; |
198 | } |
199 | |
200 | /* |
201 | * The first byte must be zero, however we must not leak if this is |
202 | * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA |
203 | * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). |
204 | */ |
205 | good = constant_time_is_zero(em[0]); |
206 | |
207 | maskedseed = em + 1; |
208 | maskeddb = em + 1 + mdlen; |
209 | |
210 | if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md)) |
211 | goto cleanup; |
212 | for (i = 0; i < mdlen; i++) |
213 | seed[i] ^= maskedseed[i]; |
214 | |
215 | if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md)) |
216 | goto cleanup; |
217 | for (i = 0; i < dblen; i++) |
218 | db[i] ^= maskeddb[i]; |
219 | |
220 | if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL)) |
221 | goto cleanup; |
222 | |
223 | good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen)); |
224 | |
225 | found_one_byte = 0; |
226 | for (i = mdlen; i < dblen; i++) { |
227 | /* |
228 | * Padding consists of a number of 0-bytes, followed by a 1. |
229 | */ |
230 | unsigned int equals1 = constant_time_eq(db[i], 1); |
231 | unsigned int equals0 = constant_time_is_zero(db[i]); |
232 | one_index = constant_time_select_int(~found_one_byte & equals1, |
233 | i, one_index); |
234 | found_one_byte |= equals1; |
235 | good &= (found_one_byte | equals0); |
236 | } |
237 | |
238 | good &= found_one_byte; |
239 | |
240 | /* |
241 | * At this point |good| is zero unless the plaintext was valid, |
242 | * so plaintext-awareness ensures timing side-channels are no longer a |
243 | * concern. |
244 | */ |
245 | msg_index = one_index + 1; |
246 | mlen = dblen - msg_index; |
247 | |
248 | /* |
249 | * For good measure, do this check in constant time as well. |
250 | */ |
251 | good &= constant_time_ge(tlen, mlen); |
252 | |
253 | /* |
254 | * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left. |
255 | * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|. |
256 | * Otherwise leave |to| unchanged. |
257 | * Copy the memory back in a way that does not reveal the size of |
258 | * the data being copied via a timing side channel. This requires copying |
259 | * parts of the buffer multiple times based on the bits set in the real |
260 | * length. Clear bits do a non-copy with identical access pattern. |
261 | * The loop below has overall complexity of O(N*log(N)). |
262 | */ |
263 | tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen), |
264 | dblen - mdlen - 1, tlen); |
265 | for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) { |
266 | mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0); |
267 | for (i = mdlen + 1; i < dblen - msg_index; i++) |
268 | db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]); |
269 | } |
270 | for (i = 0; i < tlen; i++) { |
271 | mask = good & constant_time_lt(i, mlen); |
272 | to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]); |
273 | } |
274 | |
275 | /* |
276 | * To avoid chosen ciphertext attacks, the error message should not |
277 | * reveal which kind of decoding error happened. |
278 | */ |
279 | RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, |
280 | RSA_R_OAEP_DECODING_ERROR); |
281 | err_clear_last_constant_time(1 & good); |
282 | cleanup: |
283 | OPENSSL_cleanse(seed, sizeof(seed)); |
284 | OPENSSL_clear_free(db, dblen); |
285 | OPENSSL_clear_free(em, num); |
286 | |
287 | return constant_time_select_int(good, mlen, -1); |
288 | } |
289 | |
290 | /* |
291 | * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B. |
292 | * The variables are named differently to NIST: |
293 | * mask (T) and len (maskLen)are the returned mask. |
294 | * seed (mgfSeed). |
295 | * The range checking steps inm the process are performed outside. |
296 | */ |
297 | int PKCS1_MGF1(unsigned char *mask, long len, |
298 | const unsigned char *seed, long seedlen, const EVP_MD *dgst) |
299 | { |
300 | long i, outlen = 0; |
301 | unsigned char cnt[4]; |
302 | EVP_MD_CTX *c = EVP_MD_CTX_new(); |
303 | unsigned char md[EVP_MAX_MD_SIZE]; |
304 | int mdlen; |
305 | int rv = -1; |
306 | |
307 | if (c == NULL) |
308 | goto err; |
309 | mdlen = EVP_MD_size(dgst); |
310 | if (mdlen < 0) |
311 | goto err; |
312 | /* step 4 */ |
313 | for (i = 0; outlen < len; i++) { |
314 | /* step 4a: D = I2BS(counter, 4) */ |
315 | cnt[0] = (unsigned char)((i >> 24) & 255); |
316 | cnt[1] = (unsigned char)((i >> 16) & 255); |
317 | cnt[2] = (unsigned char)((i >> 8)) & 255; |
318 | cnt[3] = (unsigned char)(i & 255); |
319 | /* step 4b: T =T || hash(mgfSeed || D) */ |
320 | if (!EVP_DigestInit_ex(c, dgst, NULL) |
321 | || !EVP_DigestUpdate(c, seed, seedlen) |
322 | || !EVP_DigestUpdate(c, cnt, 4)) |
323 | goto err; |
324 | if (outlen + mdlen <= len) { |
325 | if (!EVP_DigestFinal_ex(c, mask + outlen, NULL)) |
326 | goto err; |
327 | outlen += mdlen; |
328 | } else { |
329 | if (!EVP_DigestFinal_ex(c, md, NULL)) |
330 | goto err; |
331 | memcpy(mask + outlen, md, len - outlen); |
332 | outlen = len; |
333 | } |
334 | } |
335 | rv = 0; |
336 | err: |
337 | OPENSSL_cleanse(md, sizeof(md)); |
338 | EVP_MD_CTX_free(c); |
339 | return rv; |
340 | } |
341 | |