1 /*
2 * Copyright 1999-2021 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 /*
24 * RSA low level APIs are deprecated for public use, but still ok for
25 * internal use.
26 */
27 #include "internal/deprecated.h"
28
29 #include "internal/constant_time.h"
30
31 #include <stdio.h>
32 #include "internal/cryptlib.h"
33 #include <openssl/bn.h>
34 #include <openssl/evp.h>
35 #include <openssl/rand.h>
36 #include <openssl/sha.h>
37 #include "rsa_local.h"
38
RSA_padding_add_PKCS1_OAEP(unsigned char * to,int tlen,const unsigned char * from,int flen,const unsigned char * param,int plen)39 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
40 const unsigned char *from, int flen,
41 const unsigned char *param, int plen)
42 {
43 return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
44 param, plen, NULL, NULL);
45 }
46
47 /*
48 * Perform the padding as per NIST 800-56B 7.2.2.3
49 * from (K) is the key material.
50 * param (A) is the additional input.
51 * Step numbers are included here but not in the constant time inverse below
52 * to avoid complicating an already difficult enough function.
53 */
ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX * libctx,unsigned char * to,int tlen,const unsigned char * from,int flen,const unsigned char * param,int plen,const EVP_MD * md,const EVP_MD * mgf1md)54 int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx,
55 unsigned char *to, int tlen,
56 const unsigned char *from, int flen,
57 const unsigned char *param,
58 int plen, const EVP_MD *md,
59 const EVP_MD *mgf1md)
60 {
61 int rv = 0;
62 int i, emlen = tlen - 1;
63 unsigned char *db, *seed;
64 unsigned char *dbmask = NULL;
65 unsigned char seedmask[EVP_MAX_MD_SIZE];
66 int mdlen, dbmask_len = 0;
67
68 if (md == NULL) {
69 #ifndef FIPS_MODULE
70 md = EVP_sha1();
71 #else
72 ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
73 return 0;
74 #endif
75 }
76 if (mgf1md == NULL)
77 mgf1md = md;
78
79 mdlen = EVP_MD_get_size(md);
80 if (mdlen <= 0) {
81 ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
82 return 0;
83 }
84
85 /* step 2b: check KLen > nLen - 2 HLen - 2 */
86 if (flen > emlen - 2 * mdlen - 1) {
87 ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
88 return 0;
89 }
90
91 if (emlen < 2 * mdlen + 1) {
92 ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);
93 return 0;
94 }
95
96 /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
97 to[0] = 0;
98 seed = to + 1;
99 db = to + mdlen + 1;
100
101 /* step 3a: hash the additional input */
102 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
103 goto err;
104 /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
105 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
106 /* step 3c: DB = HA || PS || 00000001 || K */
107 db[emlen - flen - mdlen - 1] = 0x01;
108 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
109 /* step 3d: generate random byte string */
110 if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0)
111 goto err;
112
113 dbmask_len = emlen - mdlen;
114 dbmask = OPENSSL_malloc(dbmask_len);
115 if (dbmask == NULL) {
116 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
117 goto err;
118 }
119
120 /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
121 if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
122 goto err;
123 /* step 3f: maskedDB = DB XOR dbMask */
124 for (i = 0; i < dbmask_len; i++)
125 db[i] ^= dbmask[i];
126
127 /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
128 if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
129 goto err;
130 /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
131 for (i = 0; i < mdlen; i++)
132 seed[i] ^= seedmask[i];
133 rv = 1;
134
135 err:
136 OPENSSL_cleanse(seedmask, sizeof(seedmask));
137 OPENSSL_clear_free(dbmask, dbmask_len);
138 return rv;
139 }
140
RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char * to,int tlen,const unsigned char * from,int flen,const unsigned char * param,int plen,const EVP_MD * md,const EVP_MD * mgf1md)141 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
142 const unsigned char *from, int flen,
143 const unsigned char *param, int plen,
144 const EVP_MD *md, const EVP_MD *mgf1md)
145 {
146 return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
147 param, plen, md, mgf1md);
148 }
149
RSA_padding_check_PKCS1_OAEP(unsigned char * to,int tlen,const unsigned char * from,int flen,int num,const unsigned char * param,int plen)150 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
151 const unsigned char *from, int flen, int num,
152 const unsigned char *param, int plen)
153 {
154 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
155 param, plen, NULL, NULL);
156 }
157
RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char * to,int tlen,const unsigned char * from,int flen,int num,const unsigned char * param,int plen,const EVP_MD * md,const EVP_MD * mgf1md)158 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
159 const unsigned char *from, int flen,
160 int num, const unsigned char *param,
161 int plen, const EVP_MD *md,
162 const EVP_MD *mgf1md)
163 {
164 int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
165 unsigned int good = 0, found_one_byte, mask;
166 const unsigned char *maskedseed, *maskeddb;
167 /*
168 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
169 * Y || maskedSeed || maskedDB
170 */
171 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
172 phash[EVP_MAX_MD_SIZE];
173 int mdlen;
174
175 if (md == NULL) {
176 #ifndef FIPS_MODULE
177 md = EVP_sha1();
178 #else
179 ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
180 return -1;
181 #endif
182 }
183
184 if (mgf1md == NULL)
185 mgf1md = md;
186
187 mdlen = EVP_MD_get_size(md);
188
189 if (tlen <= 0 || flen <= 0)
190 return -1;
191 /*
192 * |num| is the length of the modulus; |flen| is the length of the
193 * encoded message. Therefore, for any |from| that was obtained by
194 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
195 * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
196 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
197 * This does not leak any side-channel information.
198 */
199 if (num < flen || num < 2 * mdlen + 2) {
200 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
201 return -1;
202 }
203
204 dblen = num - mdlen - 1;
205 db = OPENSSL_malloc(dblen);
206 if (db == NULL) {
207 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
208 goto cleanup;
209 }
210
211 em = OPENSSL_malloc(num);
212 if (em == NULL) {
213 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
214 goto cleanup;
215 }
216
217 /*
218 * Caller is encouraged to pass zero-padded message created with
219 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
220 * bounds, it's impossible to have an invariant memory access pattern
221 * in case |from| was not zero-padded in advance.
222 */
223 for (from += flen, em += num, i = 0; i < num; i++) {
224 mask = ~constant_time_is_zero(flen);
225 flen -= 1 & mask;
226 from -= 1 & mask;
227 *--em = *from & mask;
228 }
229
230 /*
231 * The first byte must be zero, however we must not leak if this is
232 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
233 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
234 */
235 good = constant_time_is_zero(em[0]);
236
237 maskedseed = em + 1;
238 maskeddb = em + 1 + mdlen;
239
240 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
241 goto cleanup;
242 for (i = 0; i < mdlen; i++)
243 seed[i] ^= maskedseed[i];
244
245 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
246 goto cleanup;
247 for (i = 0; i < dblen; i++)
248 db[i] ^= maskeddb[i];
249
250 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
251 goto cleanup;
252
253 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
254
255 found_one_byte = 0;
256 for (i = mdlen; i < dblen; i++) {
257 /*
258 * Padding consists of a number of 0-bytes, followed by a 1.
259 */
260 unsigned int equals1 = constant_time_eq(db[i], 1);
261 unsigned int equals0 = constant_time_is_zero(db[i]);
262 one_index = constant_time_select_int(~found_one_byte & equals1,
263 i, one_index);
264 found_one_byte |= equals1;
265 good &= (found_one_byte | equals0);
266 }
267
268 good &= found_one_byte;
269
270 /*
271 * At this point |good| is zero unless the plaintext was valid,
272 * so plaintext-awareness ensures timing side-channels are no longer a
273 * concern.
274 */
275 msg_index = one_index + 1;
276 mlen = dblen - msg_index;
277
278 /*
279 * For good measure, do this check in constant time as well.
280 */
281 good &= constant_time_ge(tlen, mlen);
282
283 /*
284 * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
285 * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
286 * Otherwise leave |to| unchanged.
287 * Copy the memory back in a way that does not reveal the size of
288 * the data being copied via a timing side channel. This requires copying
289 * parts of the buffer multiple times based on the bits set in the real
290 * length. Clear bits do a non-copy with identical access pattern.
291 * The loop below has overall complexity of O(N*log(N)).
292 */
293 tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
294 dblen - mdlen - 1, tlen);
295 for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
296 mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
297 for (i = mdlen + 1; i < dblen - msg_index; i++)
298 db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
299 }
300 for (i = 0; i < tlen; i++) {
301 mask = good & constant_time_lt(i, mlen);
302 to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
303 }
304
305 #ifndef FIPS_MODULE
306 /*
307 * To avoid chosen ciphertext attacks, the error message should not
308 * reveal which kind of decoding error happened.
309 *
310 * This trick doesn't work in the FIPS provider because libcrypto manages
311 * the error stack. Instead we opt not to put an error on the stack at all
312 * in case of padding failure in the FIPS provider.
313 */
314 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
315 err_clear_last_constant_time(1 & good);
316 #endif
317 cleanup:
318 OPENSSL_cleanse(seed, sizeof(seed));
319 OPENSSL_clear_free(db, dblen);
320 OPENSSL_clear_free(em, num);
321
322 return constant_time_select_int(good, mlen, -1);
323 }
324
325 /*
326 * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
327 * The variables are named differently to NIST:
328 * mask (T) and len (maskLen)are the returned mask.
329 * seed (mgfSeed).
330 * The range checking steps inm the process are performed outside.
331 */
PKCS1_MGF1(unsigned char * mask,long len,const unsigned char * seed,long seedlen,const EVP_MD * dgst)332 int PKCS1_MGF1(unsigned char *mask, long len,
333 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
334 {
335 long i, outlen = 0;
336 unsigned char cnt[4];
337 EVP_MD_CTX *c = EVP_MD_CTX_new();
338 unsigned char md[EVP_MAX_MD_SIZE];
339 int mdlen;
340 int rv = -1;
341
342 if (c == NULL)
343 goto err;
344 mdlen = EVP_MD_get_size(dgst);
345 if (mdlen < 0)
346 goto err;
347 /* step 4 */
348 for (i = 0; outlen < len; i++) {
349 /* step 4a: D = I2BS(counter, 4) */
350 cnt[0] = (unsigned char)((i >> 24) & 255);
351 cnt[1] = (unsigned char)((i >> 16) & 255);
352 cnt[2] = (unsigned char)((i >> 8)) & 255;
353 cnt[3] = (unsigned char)(i & 255);
354 /* step 4b: T =T || hash(mgfSeed || D) */
355 if (!EVP_DigestInit_ex(c, dgst, NULL)
356 || !EVP_DigestUpdate(c, seed, seedlen)
357 || !EVP_DigestUpdate(c, cnt, 4))
358 goto err;
359 if (outlen + mdlen <= len) {
360 if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
361 goto err;
362 outlen += mdlen;
363 } else {
364 if (!EVP_DigestFinal_ex(c, md, NULL))
365 goto err;
366 memcpy(mask + outlen, md, len - outlen);
367 outlen = len;
368 }
369 }
370 rv = 0;
371 err:
372 OPENSSL_cleanse(md, sizeof(md));
373 EVP_MD_CTX_free(c);
374 return rv;
375 }
376