2 * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
3 * WITHOUT WARRANTY OF ANY KIND, either express or implied.
6 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
9 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
10 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
11 * proof for the original OAEP scheme, which EME-OAEP is based on. A new
12 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
13 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
14 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
15 * for the underlying permutation: "partial-one-wayness" instead of
16 * one-wayness. For the RSA function, this is an equivalent notion.
19 #include "internal/constant_time_locl.h"
22 #include "internal/cryptlib.h"
23 #include <openssl/bn.h>
24 #include <openssl/rsa.h>
25 #include <openssl/evp.h>
26 #include <openssl/rand.h>
27 #include <openssl/sha.h>
29 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
30 const unsigned char *from, int flen,
31 const unsigned char *param, int plen)
33 return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
34 param, plen, NULL, NULL);
37 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
38 const unsigned char *from, int flen,
39 const unsigned char *param, int plen,
40 const EVP_MD *md, const EVP_MD *mgf1md)
42 int i, emlen = tlen - 1;
43 unsigned char *db, *seed;
44 unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
52 mdlen = EVP_MD_size(md);
54 if (flen > emlen - 2 * mdlen - 1) {
55 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
56 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
60 if (emlen < 2 * mdlen + 1) {
61 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
62 RSA_R_KEY_SIZE_TOO_SMALL);
70 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
72 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
73 db[emlen - flen - mdlen - 1] = 0x01;
74 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
75 if (RAND_bytes(seed, mdlen) <= 0)
79 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
83 dbmask = OPENSSL_malloc(emlen - mdlen);
85 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
89 if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
91 for (i = 0; i < emlen - mdlen; i++)
94 if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
96 for (i = 0; i < mdlen; i++)
97 seed[i] ^= seedmask[i];
103 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
104 const unsigned char *from, int flen, int num,
105 const unsigned char *param, int plen)
107 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
108 param, plen, NULL, NULL);
111 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
112 const unsigned char *from, int flen,
113 int num, const unsigned char *param,
114 int plen, const EVP_MD *md,
115 const EVP_MD *mgf1md)
117 int i, dblen, mlen = -1, one_index = 0, msg_index;
118 unsigned int good, found_one_byte;
119 const unsigned char *maskedseed, *maskeddb;
121 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
122 * Y || maskedSeed || maskedDB
124 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
125 phash[EVP_MAX_MD_SIZE];
133 mdlen = EVP_MD_size(md);
135 if (tlen <= 0 || flen <= 0)
138 * |num| is the length of the modulus; |flen| is the length of the
139 * encoded message. Therefore, for any |from| that was obtained by
140 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
141 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
142 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
143 * This does not leak any side-channel information.
145 if (num < flen || num < 2 * mdlen + 2)
148 dblen = num - mdlen - 1;
149 db = OPENSSL_malloc(dblen);
150 em = OPENSSL_malloc(num);
151 if (db == NULL || em == NULL) {
152 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
157 * Always do this zero-padding copy (even when num == flen) to avoid
158 * leaking that information. The copy still leaks some side-channel
159 * information, but it's impossible to have a fixed memory access
160 * pattern since we can't read out of the bounds of |from|.
162 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
165 memcpy(em + num - flen, from, flen);
168 * The first byte must be zero, however we must not leak if this is
169 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
170 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
172 good = constant_time_is_zero(em[0]);
175 maskeddb = em + 1 + mdlen;
177 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
179 for (i = 0; i < mdlen; i++)
180 seed[i] ^= maskedseed[i];
182 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
184 for (i = 0; i < dblen; i++)
185 db[i] ^= maskeddb[i];
187 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
190 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
193 for (i = mdlen; i < dblen; i++) {
195 * Padding consists of a number of 0-bytes, followed by a 1.
197 unsigned int equals1 = constant_time_eq(db[i], 1);
198 unsigned int equals0 = constant_time_is_zero(db[i]);
199 one_index = constant_time_select_int(~found_one_byte & equals1,
201 found_one_byte |= equals1;
202 good &= (found_one_byte | equals0);
205 good &= found_one_byte;
208 * At this point |good| is zero unless the plaintext was valid,
209 * so plaintext-awareness ensures timing side-channels are no longer a
215 msg_index = one_index + 1;
216 mlen = dblen - msg_index;
219 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
222 memcpy(to, db + msg_index, mlen);
228 * To avoid chosen ciphertext attacks, the error message should not
229 * reveal which kind of decoding error happened.
231 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
232 RSA_R_OAEP_DECODING_ERROR);
239 int PKCS1_MGF1(unsigned char *mask, long len,
240 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
243 unsigned char cnt[4];
244 EVP_MD_CTX *c = EVP_MD_CTX_new();
245 unsigned char md[EVP_MAX_MD_SIZE];
251 mdlen = 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);