1 /*
2 * Copyright 1999-2024 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 #ifdef FIPS_MODULE
80 /* XOF are approved as standalone; Shake256 in Ed448; MGF */
81 if (EVP_MD_xof(md)) {
82 ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);
83 return 0;
84 }
85 if (EVP_MD_xof(mgf1md)) {
86 ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);
87 return 0;
88 }
89 #endif
90
91 mdlen = EVP_MD_get_size(md);
92 if (mdlen <= 0) {
93 ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
94 return 0;
95 }
96
97 /* step 2b: check KLen > nLen - 2 HLen - 2 */
98 if (flen > emlen - 2 * mdlen - 1) {
99 ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
100 return 0;
101 }
102
103 if (emlen < 2 * mdlen + 1) {
104 ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);
105 return 0;
106 }
107
108 /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
109 to[0] = 0;
110 seed = to + 1;
111 db = to + mdlen + 1;
112
113 /* step 3a: hash the additional input */
114 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
115 goto err;
116 /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
117 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
118 /* step 3c: DB = HA || PS || 00000001 || K */
119 db[emlen - flen - mdlen - 1] = 0x01;
120 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
121 /* step 3d: generate random byte string */
122 if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0)
123 goto err;
124
125 dbmask_len = emlen - mdlen;
126 dbmask = OPENSSL_malloc(dbmask_len);
127 if (dbmask == NULL)
128 goto err;
129
130 /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
131 if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
132 goto err;
133 /* step 3f: maskedDB = DB XOR dbMask */
134 for (i = 0; i < dbmask_len; i++)
135 db[i] ^= dbmask[i];
136
137 /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
138 if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
139 goto err;
140 /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
141 for (i = 0; i < mdlen; i++)
142 seed[i] ^= seedmask[i];
143 rv = 1;
144
145 err:
146 OPENSSL_cleanse(seedmask, sizeof(seedmask));
147 OPENSSL_clear_free(dbmask, dbmask_len);
148 return rv;
149 }
150
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)151 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
152 const unsigned char *from, int flen,
153 const unsigned char *param, int plen,
154 const EVP_MD *md, const EVP_MD *mgf1md)
155 {
156 return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
157 param, plen, md, mgf1md);
158 }
159
RSA_padding_check_PKCS1_OAEP(unsigned char * to,int tlen,const unsigned char * from,int flen,int num,const unsigned char * param,int plen)160 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
161 const unsigned char *from, int flen, int num,
162 const unsigned char *param, int plen)
163 {
164 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
165 param, plen, NULL, NULL);
166 }
167
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)168 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
169 const unsigned char *from, int flen,
170 int num, const unsigned char *param,
171 int plen, const EVP_MD *md,
172 const EVP_MD *mgf1md)
173 {
174 int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
175 unsigned int good = 0, found_one_byte, mask;
176 const unsigned char *maskedseed, *maskeddb;
177 /*
178 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
179 * Y || maskedSeed || maskedDB
180 */
181 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
182 phash[EVP_MAX_MD_SIZE];
183 int mdlen;
184
185 if (md == NULL) {
186 #ifndef FIPS_MODULE
187 md = EVP_sha1();
188 #else
189 ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
190 return -1;
191 #endif
192 }
193
194 if (mgf1md == NULL)
195 mgf1md = md;
196
197 #ifdef FIPS_MODULE
198 /* XOF are approved as standalone; Shake256 in Ed448; MGF */
199 if (EVP_MD_xof(md)) {
200 ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);
201 return -1;
202 }
203 if (EVP_MD_xof(mgf1md)) {
204 ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);
205 return -1;
206 }
207 #endif
208
209 mdlen = EVP_MD_get_size(md);
210
211 if (tlen <= 0 || flen <= 0 || mdlen <= 0)
212 return -1;
213 /*
214 * |num| is the length of the modulus; |flen| is the length of the
215 * encoded message. Therefore, for any |from| that was obtained by
216 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
217 * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
218 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
219 * This does not leak any side-channel information.
220 */
221 if (num < flen || num < 2 * mdlen + 2) {
222 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
223 return -1;
224 }
225
226 dblen = num - mdlen - 1;
227 db = OPENSSL_malloc(dblen);
228 if (db == NULL)
229 goto cleanup;
230
231 em = OPENSSL_malloc(num);
232 if (em == NULL)
233 goto cleanup;
234
235 /*
236 * Caller is encouraged to pass zero-padded message created with
237 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
238 * bounds, it's impossible to have an invariant memory access pattern
239 * in case |from| was not zero-padded in advance.
240 */
241 for (from += flen, em += num, i = 0; i < num; i++) {
242 mask = ~constant_time_is_zero(flen);
243 flen -= 1 & mask;
244 from -= 1 & mask;
245 *--em = *from & mask;
246 }
247
248 /*
249 * The first byte must be zero, however we must not leak if this is
250 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
251 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
252 */
253 good = constant_time_is_zero(em[0]);
254
255 maskedseed = em + 1;
256 maskeddb = em + 1 + mdlen;
257
258 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
259 goto cleanup;
260 for (i = 0; i < mdlen; i++)
261 seed[i] ^= maskedseed[i];
262
263 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
264 goto cleanup;
265 for (i = 0; i < dblen; i++)
266 db[i] ^= maskeddb[i];
267
268 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
269 goto cleanup;
270
271 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
272
273 found_one_byte = 0;
274 for (i = mdlen; i < dblen; i++) {
275 /*
276 * Padding consists of a number of 0-bytes, followed by a 1.
277 */
278 unsigned int equals1 = constant_time_eq(db[i], 1);
279 unsigned int equals0 = constant_time_is_zero(db[i]);
280 one_index = constant_time_select_int(~found_one_byte & equals1,
281 i, one_index);
282 found_one_byte |= equals1;
283 good &= (found_one_byte | equals0);
284 }
285
286 good &= found_one_byte;
287
288 /*
289 * At this point |good| is zero unless the plaintext was valid,
290 * so plaintext-awareness ensures timing side-channels are no longer a
291 * concern.
292 */
293 msg_index = one_index + 1;
294 mlen = dblen - msg_index;
295
296 /*
297 * For good measure, do this check in constant time as well.
298 */
299 good &= constant_time_ge(tlen, mlen);
300
301 /*
302 * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
303 * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
304 * Otherwise leave |to| unchanged.
305 * Copy the memory back in a way that does not reveal the size of
306 * the data being copied via a timing side channel. This requires copying
307 * parts of the buffer multiple times based on the bits set in the real
308 * length. Clear bits do a non-copy with identical access pattern.
309 * The loop below has overall complexity of O(N*log(N)).
310 */
311 tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
312 dblen - mdlen - 1, tlen);
313 for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
314 mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
315 for (i = mdlen + 1; i < dblen - msg_index; i++)
316 db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
317 }
318 for (i = 0; i < tlen; i++) {
319 mask = good & constant_time_lt(i, mlen);
320 to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
321 }
322
323 #ifndef FIPS_MODULE
324 /*
325 * To avoid chosen ciphertext attacks, the error message should not
326 * reveal which kind of decoding error happened.
327 *
328 * This trick doesn't work in the FIPS provider because libcrypto manages
329 * the error stack. Instead we opt not to put an error on the stack at all
330 * in case of padding failure in the FIPS provider.
331 */
332 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
333 err_clear_last_constant_time(1 & good);
334 #endif
335 cleanup:
336 OPENSSL_cleanse(seed, sizeof(seed));
337 OPENSSL_clear_free(db, dblen);
338 OPENSSL_clear_free(em, num);
339
340 return constant_time_select_int(good, mlen, -1);
341 }
342
343 /*
344 * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
345 * The variables are named differently to NIST:
346 * mask (T) and len (maskLen)are the returned mask.
347 * seed (mgfSeed).
348 * The range checking steps inm the process are performed outside.
349 */
PKCS1_MGF1(unsigned char * mask,long len,const unsigned char * seed,long seedlen,const EVP_MD * dgst)350 int PKCS1_MGF1(unsigned char *mask, long len,
351 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
352 {
353 long i, outlen = 0;
354 unsigned char cnt[4];
355 EVP_MD_CTX *c = EVP_MD_CTX_new();
356 unsigned char md[EVP_MAX_MD_SIZE];
357 int mdlen;
358 int rv = -1;
359
360 if (c == NULL)
361 goto err;
362 mdlen = EVP_MD_get_size(dgst);
363 if (mdlen <= 0)
364 goto err;
365 /* step 4 */
366 for (i = 0; outlen < len; i++) {
367 /* step 4a: D = I2BS(counter, 4) */
368 cnt[0] = (unsigned char)((i >> 24) & 255);
369 cnt[1] = (unsigned char)((i >> 16) & 255);
370 cnt[2] = (unsigned char)((i >> 8)) & 255;
371 cnt[3] = (unsigned char)(i & 255);
372 /* step 4b: T =T || hash(mgfSeed || D) */
373 if (!EVP_DigestInit_ex(c, dgst, NULL)
374 || !EVP_DigestUpdate(c, seed, seedlen)
375 || !EVP_DigestUpdate(c, cnt, 4))
376 goto err;
377 if (outlen + mdlen <= len) {
378 if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
379 goto err;
380 outlen += mdlen;
381 } else {
382 if (!EVP_DigestFinal_ex(c, md, NULL))
383 goto err;
384 memcpy(mask + outlen, md, len - outlen);
385 outlen = len;
386 }
387 }
388 rv = 0;
389 err:
390 OPENSSL_cleanse(md, sizeof(md));
391 EVP_MD_CTX_free(c);
392 return rv;
393 }
394
