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
33int 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 */
48int 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
125int 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
133int 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 */
297int 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