rsa_oaep.c revision 325337 
1/* crypto/rsa/rsa_oaep.c */
2/*
3 * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
4 * WITHOUT WARRANTY OF ANY KIND, either express or implied.
5 */
6
7/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
8
9/*
10 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
11 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
12 * proof for the original OAEP scheme, which EME-OAEP is based on. A new
13 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
14 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
15 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
16 * for the underlying permutation: "partial-one-wayness" instead of
17 * one-wayness.  For the RSA function, this is an equivalent notion.
18 */
19
20#include "constant_time_locl.h"
21
22#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
23# include <stdio.h>
24# include "cryptlib.h"
25# include <openssl/bn.h>
26# include <openssl/rsa.h>
27# include <openssl/evp.h>
28# include <openssl/rand.h>
29# include <openssl/sha.h>
30
31int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
32                               const unsigned char *from, int flen,
33                               const unsigned char *param, int plen)
34{
35    return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
36                                           param, plen, NULL, NULL);
37}
38
39int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
40                                    const unsigned char *from, int flen,
41                                    const unsigned char *param, int plen,
42                                    const EVP_MD *md, const EVP_MD *mgf1md)
43{
44    int i, emlen = tlen - 1;
45    unsigned char *db, *seed;
46    unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
47    int mdlen;
48
49    if (md == NULL)
50        md = EVP_sha1();
51    if (mgf1md == NULL)
52        mgf1md = md;
53
54    mdlen = EVP_MD_size(md);
55
56    if (flen > emlen - 2 * mdlen - 1) {
57        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
58               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
59        return 0;
60    }
61
62    if (emlen < 2 * mdlen + 1) {
63        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
64               RSA_R_KEY_SIZE_TOO_SMALL);
65        return 0;
66    }
67
68    to[0] = 0;
69    seed = to + 1;
70    db = to + mdlen + 1;
71
72    if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
73        return 0;
74    memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
75    db[emlen - flen - mdlen - 1] = 0x01;
76    memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
77    if (RAND_bytes(seed, mdlen) <= 0)
78        return 0;
79# ifdef PKCS_TESTVECT
80    memcpy(seed,
81           "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
82           20);
83# endif
84
85    dbmask = OPENSSL_malloc(emlen - mdlen);
86    if (dbmask == NULL) {
87        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
88        return 0;
89    }
90
91    if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
92        goto err;
93    for (i = 0; i < emlen - mdlen; i++)
94        db[i] ^= dbmask[i];
95
96    if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
97        goto err;
98    for (i = 0; i < mdlen; i++)
99        seed[i] ^= seedmask[i];
100
101    OPENSSL_free(dbmask);
102    return 1;
103
104 err:
105    OPENSSL_free(dbmask);
106    return 0;
107}
108
109int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
110                                 const unsigned char *from, int flen, int num,
111                                 const unsigned char *param, int plen)
112{
113    return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
114                                             param, plen, NULL, NULL);
115}
116
117int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
118                                      const unsigned char *from, int flen,
119                                      int num, const unsigned char *param,
120                                      int plen, const EVP_MD *md,
121                                      const EVP_MD *mgf1md)
122{
123    int i, dblen, mlen = -1, one_index = 0, msg_index;
124    unsigned int good, found_one_byte;
125    const unsigned char *maskedseed, *maskeddb;
126    /*
127     * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
128     * Y || maskedSeed || maskedDB
129     */
130    unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
131        phash[EVP_MAX_MD_SIZE];
132    int mdlen;
133
134    if (md == NULL)
135        md = EVP_sha1();
136    if (mgf1md == NULL)
137        mgf1md = md;
138
139    mdlen = EVP_MD_size(md);
140
141    if (tlen <= 0 || flen <= 0)
142        return -1;
143    /*
144     * |num| is the length of the modulus; |flen| is the length of the
145     * encoded message. Therefore, for any |from| that was obtained by
146     * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
147     * num < 2 * mdlen + 2 must hold for the modulus irrespective of
148     * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
149     * This does not leak any side-channel information.
150     */
151    if (num < flen || num < 2 * mdlen + 2)
152        goto decoding_err;
153
154    dblen = num - mdlen - 1;
155    db = OPENSSL_malloc(dblen);
156    em = OPENSSL_malloc(num);
157    if (db == NULL || em == NULL) {
158        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
159        goto cleanup;
160    }
161
162    /*
163     * Always do this zero-padding copy (even when num == flen) to avoid
164     * leaking that information. The copy still leaks some side-channel
165     * information, but it's impossible to have a fixed  memory access
166     * pattern since we can't read out of the bounds of |from|.
167     *
168     * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
169     */
170    memset(em, 0, num);
171    memcpy(em + num - flen, from, flen);
172
173    /*
174     * The first byte must be zero, however we must not leak if this is
175     * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
176     * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
177     */
178    good = constant_time_is_zero(em[0]);
179
180    maskedseed = em + 1;
181    maskeddb = em + 1 + mdlen;
182
183    if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
184        goto cleanup;
185    for (i = 0; i < mdlen; i++)
186        seed[i] ^= maskedseed[i];
187
188    if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
189        goto cleanup;
190    for (i = 0; i < dblen; i++)
191        db[i] ^= maskeddb[i];
192
193    if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
194        goto cleanup;
195
196    good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
197
198    found_one_byte = 0;
199    for (i = mdlen; i < dblen; i++) {
200        /*
201         * Padding consists of a number of 0-bytes, followed by a 1.
202         */
203        unsigned int equals1 = constant_time_eq(db[i], 1);
204        unsigned int equals0 = constant_time_is_zero(db[i]);
205        one_index = constant_time_select_int(~found_one_byte & equals1,
206                                             i, one_index);
207        found_one_byte |= equals1;
208        good &= (found_one_byte | equals0);
209    }
210
211    good &= found_one_byte;
212
213    /*
214     * At this point |good| is zero unless the plaintext was valid,
215     * so plaintext-awareness ensures timing side-channels are no longer a
216     * concern.
217     */
218    if (!good)
219        goto decoding_err;
220
221    msg_index = one_index + 1;
222    mlen = dblen - msg_index;
223
224    if (tlen < mlen) {
225        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
226        mlen = -1;
227    } else {
228        memcpy(to, db + msg_index, mlen);
229        goto cleanup;
230    }
231
232 decoding_err:
233    /*
234     * To avoid chosen ciphertext attacks, the error message should not
235     * reveal which kind of decoding error happened.
236     */
237    RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
238           RSA_R_OAEP_DECODING_ERROR);
239 cleanup:
240    if (db != NULL) {
241        OPENSSL_cleanse(db, dblen);
242        OPENSSL_free(db);
243    }
244    if (em != NULL) {
245        OPENSSL_cleanse(em, num);
246        OPENSSL_free(em);
247    }
248    return mlen;
249}
250
251int PKCS1_MGF1(unsigned char *mask, long len,
252               const unsigned char *seed, long seedlen, const EVP_MD *dgst)
253{
254    long i, outlen = 0;
255    unsigned char cnt[4];
256    EVP_MD_CTX c;
257    unsigned char md[EVP_MAX_MD_SIZE];
258    int mdlen;
259    int rv = -1;
260
261    EVP_MD_CTX_init(&c);
262    mdlen = EVP_MD_size(dgst);
263    if (mdlen < 0)
264        goto err;
265    for (i = 0; outlen < len; i++) {
266        cnt[0] = (unsigned char)((i >> 24) & 255);
267        cnt[1] = (unsigned char)((i >> 16) & 255);
268        cnt[2] = (unsigned char)((i >> 8)) & 255;
269        cnt[3] = (unsigned char)(i & 255);
270        if (!EVP_DigestInit_ex(&c, dgst, NULL)
271            || !EVP_DigestUpdate(&c, seed, seedlen)
272            || !EVP_DigestUpdate(&c, cnt, 4))
273            goto err;
274        if (outlen + mdlen <= len) {
275            if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
276                goto err;
277            outlen += mdlen;
278        } else {
279            if (!EVP_DigestFinal_ex(&c, md, NULL))
280                goto err;
281            memcpy(mask + outlen, md, len - outlen);
282            outlen = len;
283        }
284    }
285    rv = 0;
286 err:
287    EVP_MD_CTX_cleanup(&c);
288    return rv;
289}
290
291#endif
292