rsa_oaep.c revision 296341 
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
31static int MGF1(unsigned char *mask, long len,
32                const unsigned char *seed, long seedlen);
33
34int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
35                               const unsigned char *from, int flen,
36                               const unsigned char *param, int plen)
37{
38    int i, emlen = tlen - 1;
39    unsigned char *db, *seed;
40    unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
41
42    if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) {
43        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
44               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
45        return 0;
46    }
47
48    if (emlen < 2 * SHA_DIGEST_LENGTH + 1) {
49        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
50        return 0;
51    }
52
53    to[0] = 0;
54    seed = to + 1;
55    db = to + SHA_DIGEST_LENGTH + 1;
56
57    if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
58        return 0;
59    memset(db + SHA_DIGEST_LENGTH, 0,
60           emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
61    db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
62    memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int)flen);
63    if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
64        return 0;
65# ifdef PKCS_TESTVECT
66    memcpy(seed,
67           "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
68           20);
69# endif
70
71    dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
72    if (dbmask == NULL) {
73        RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
74        return 0;
75    }
76
77    if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0)
78        return 0;
79    for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
80        db[i] ^= dbmask[i];
81
82    if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0)
83        return 0;
84    for (i = 0; i < SHA_DIGEST_LENGTH; i++)
85        seed[i] ^= seedmask[i];
86
87    OPENSSL_free(dbmask);
88    return 1;
89}
90
91int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
92                                 const unsigned char *from, int flen, int num,
93                                 const unsigned char *param, int plen)
94{
95    int i, dblen, mlen = -1, one_index = 0, msg_index;
96    unsigned int good, found_one_byte;
97    const unsigned char *maskedseed, *maskeddb;
98    /*
99     * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
100     * Y || maskedSeed || maskedDB
101     */
102    unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
103        phash[EVP_MAX_MD_SIZE];
104
105    if (tlen <= 0 || flen <= 0)
106        return -1;
107
108    /*
109     * |num| is the length of the modulus; |flen| is the length of the
110     * encoded message. Therefore, for any |from| that was obtained by
111     * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
112     * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus
113     * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2.
114     * This does not leak any side-channel information.
115     */
116    if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2)
117        goto decoding_err;
118
119    dblen = num - SHA_DIGEST_LENGTH - 1;
120    db = OPENSSL_malloc(dblen);
121    em = OPENSSL_malloc(num);
122    if (db == NULL || em == NULL) {
123        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
124        goto cleanup;
125    }
126
127    /*
128     * Always do this zero-padding copy (even when num == flen) to avoid
129     * leaking that information. The copy still leaks some side-channel
130     * information, but it's impossible to have a fixed  memory access
131     * pattern since we can't read out of the bounds of |from|.
132     *
133     * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
134     */
135    memset(em, 0, num);
136    memcpy(em + num - flen, from, flen);
137
138    /*
139     * The first byte must be zero, however we must not leak if this is
140     * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
141     * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
142     */
143    good = constant_time_is_zero(em[0]);
144
145    maskedseed = em + 1;
146    maskeddb = em + 1 + SHA_DIGEST_LENGTH;
147
148    if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
149        goto cleanup;
150    for (i = 0; i < SHA_DIGEST_LENGTH; i++)
151        seed[i] ^= maskedseed[i];
152
153    if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
154        goto cleanup;
155    for (i = 0; i < dblen; i++)
156        db[i] ^= maskeddb[i];
157
158    if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
159        goto cleanup;
160
161    good &=
162        constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH));
163
164    found_one_byte = 0;
165    for (i = SHA_DIGEST_LENGTH; i < dblen; i++) {
166        /*
167         * Padding consists of a number of 0-bytes, followed by a 1.
168         */
169        unsigned int equals1 = constant_time_eq(db[i], 1);
170        unsigned int equals0 = constant_time_is_zero(db[i]);
171        one_index = constant_time_select_int(~found_one_byte & equals1,
172                                             i, one_index);
173        found_one_byte |= equals1;
174        good &= (found_one_byte | equals0);
175    }
176
177    good &= found_one_byte;
178
179    /*
180     * At this point |good| is zero unless the plaintext was valid,
181     * so plaintext-awareness ensures timing side-channels are no longer a
182     * concern.
183     */
184    if (!good)
185        goto decoding_err;
186
187    msg_index = one_index + 1;
188    mlen = dblen - msg_index;
189
190    if (tlen < mlen) {
191        RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
192        mlen = -1;
193    } else {
194        memcpy(to, db + msg_index, mlen);
195        goto cleanup;
196    }
197
198 decoding_err:
199    /*
200     * To avoid chosen ciphertext attacks, the error message should not
201     * reveal which kind of decoding error happened.
202     */
203    RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
204 cleanup:
205    if (db != NULL)
206        OPENSSL_free(db);
207    if (em != NULL)
208        OPENSSL_free(em);
209    return mlen;
210}
211
212int PKCS1_MGF1(unsigned char *mask, long len,
213               const unsigned char *seed, long seedlen, const EVP_MD *dgst)
214{
215    long i, outlen = 0;
216    unsigned char cnt[4];
217    EVP_MD_CTX c;
218    unsigned char md[EVP_MAX_MD_SIZE];
219    int mdlen;
220    int rv = -1;
221
222    EVP_MD_CTX_init(&c);
223    mdlen = EVP_MD_size(dgst);
224    if (mdlen < 0)
225        goto err;
226    for (i = 0; outlen < len; i++) {
227        cnt[0] = (unsigned char)((i >> 24) & 255);
228        cnt[1] = (unsigned char)((i >> 16) & 255);
229        cnt[2] = (unsigned char)((i >> 8)) & 255;
230        cnt[3] = (unsigned char)(i & 255);
231        if (!EVP_DigestInit_ex(&c, dgst, NULL)
232            || !EVP_DigestUpdate(&c, seed, seedlen)
233            || !EVP_DigestUpdate(&c, cnt, 4))
234            goto err;
235        if (outlen + mdlen <= len) {
236            if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
237                goto err;
238            outlen += mdlen;
239        } else {
240            if (!EVP_DigestFinal_ex(&c, md, NULL))
241                goto err;
242            memcpy(mask + outlen, md, len - outlen);
243            outlen = len;
244        }
245    }
246    rv = 0;
247 err:
248    EVP_MD_CTX_cleanup(&c);
249    return rv;
250}
251
252static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
253                long seedlen)
254{
255    return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
256}
257#endif
258