1 /* crypto/rsa/rsa_oaep.c */
3 * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
4 * WITHOUT WARRANTY OF ANY KIND, either express or implied.
7 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
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.
20 #include "internal/constant_time_locl.h"
24 #include <openssl/bn.h>
25 #include <openssl/rsa.h>
26 #include <openssl/evp.h>
27 #include <openssl/rand.h>
28 #include <openssl/sha.h>
30 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
31 const unsigned char *from, int flen,
32 const unsigned char *param, int plen)
34 return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
35 param, plen, NULL, NULL);
38 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
39 const unsigned char *from, int flen,
40 const unsigned char *param, int plen,
41 const EVP_MD *md, const EVP_MD *mgf1md)
43 int i, emlen = tlen - 1;
44 unsigned char *db, *seed;
45 unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
53 mdlen = EVP_MD_size(md);
55 if (flen > emlen - 2 * mdlen - 1) {
56 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
57 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
61 if (emlen < 2 * mdlen + 1) {
62 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
63 RSA_R_KEY_SIZE_TOO_SMALL);
71 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
73 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
74 db[emlen - flen - mdlen - 1] = 0x01;
75 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
76 if (RAND_bytes(seed, mdlen) <= 0)
80 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
84 dbmask = OPENSSL_malloc(emlen - mdlen);
86 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
90 if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
92 for (i = 0; i < emlen - mdlen; i++)
95 if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
97 for (i = 0; i < mdlen; i++)
98 seed[i] ^= seedmask[i];
100 OPENSSL_free(dbmask);
104 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
105 const unsigned char *from, int flen, int num,
106 const unsigned char *param, int plen)
108 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
109 param, plen, NULL, NULL);
112 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
113 const unsigned char *from, int flen,
114 int num, const unsigned char *param,
115 int plen, const EVP_MD *md,
116 const EVP_MD *mgf1md)
118 int i, dblen, mlen = -1, one_index = 0, msg_index;
119 unsigned int good, found_one_byte;
120 const unsigned char *maskedseed, *maskeddb;
122 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
123 * Y || maskedSeed || maskedDB
125 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
126 phash[EVP_MAX_MD_SIZE];
134 mdlen = EVP_MD_size(md);
136 if (tlen <= 0 || flen <= 0)
139 * |num| is the length of the modulus; |flen| is the length of the
140 * encoded message. Therefore, for any |from| that was obtained by
141 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
142 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
143 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
144 * This does not leak any side-channel information.
146 if (num < flen || num < 2 * mdlen + 2)
149 dblen = num - mdlen - 1;
150 db = OPENSSL_malloc(dblen);
151 em = OPENSSL_malloc(num);
152 if (db == NULL || em == NULL) {
153 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
158 * Always do this zero-padding copy (even when num == flen) to avoid
159 * leaking that information. The copy still leaks some side-channel
160 * information, but it's impossible to have a fixed memory access
161 * pattern since we can't read out of the bounds of |from|.
163 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
166 memcpy(em + num - flen, from, flen);
169 * The first byte must be zero, however we must not leak if this is
170 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
171 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
173 good = constant_time_is_zero(em[0]);
176 maskeddb = em + 1 + mdlen;
178 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
180 for (i = 0; i < mdlen; i++)
181 seed[i] ^= maskedseed[i];
183 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
185 for (i = 0; i < dblen; i++)
186 db[i] ^= maskeddb[i];
188 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
191 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
194 for (i = mdlen; i < dblen; i++) {
196 * Padding consists of a number of 0-bytes, followed by a 1.
198 unsigned int equals1 = constant_time_eq(db[i], 1);
199 unsigned int equals0 = constant_time_is_zero(db[i]);
200 one_index = constant_time_select_int(~found_one_byte & equals1,
202 found_one_byte |= equals1;
203 good &= (found_one_byte | equals0);
206 good &= found_one_byte;
209 * At this point |good| is zero unless the plaintext was valid,
210 * so plaintext-awareness ensures timing side-channels are no longer a
216 msg_index = one_index + 1;
217 mlen = dblen - msg_index;
220 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
223 memcpy(to, db + msg_index, mlen);
229 * To avoid chosen ciphertext attacks, the error message should not
230 * reveal which kind of decoding error happened.
232 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
233 RSA_R_OAEP_DECODING_ERROR);
240 int PKCS1_MGF1(unsigned char *mask, long len,
241 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
244 unsigned char cnt[4];
246 unsigned char md[EVP_MAX_MD_SIZE];
251 mdlen = M_EVP_MD_size(dgst);
254 for (i = 0; outlen < len; i++) {
255 cnt[0] = (unsigned char)((i >> 24) & 255);
256 cnt[1] = (unsigned char)((i >> 16) & 255);
257 cnt[2] = (unsigned char)((i >> 8)) & 255;
258 cnt[3] = (unsigned char)(i & 255);
259 if (!EVP_DigestInit_ex(&c, dgst, NULL)
260 || !EVP_DigestUpdate(&c, seed, seedlen)
261 || !EVP_DigestUpdate(&c, cnt, 4))
263 if (outlen + mdlen <= len) {
264 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
268 if (!EVP_DigestFinal_ex(&c, md, NULL))
270 memcpy(mask + outlen, md, len - outlen);
276 EVP_MD_CTX_cleanup(&c);