xref: /openssl/crypto/rsa/rsa_oaep.c (revision 7ed6de99)
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