2 * Copyright 1999-2018 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the OpenSSL license (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
10 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
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.
23 #include "internal/constant_time_locl.h"
26 #include "internal/cryptlib.h"
27 #include <openssl/bn.h>
28 #include <openssl/evp.h>
29 #include <openssl/rand.h>
30 #include <openssl/sha.h>
33 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
34 const unsigned char *from, int flen,
35 const unsigned char *param, int plen)
37 return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
38 param, plen, NULL, NULL);
41 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
42 const unsigned char *from, int flen,
43 const unsigned char *param, int plen,
44 const EVP_MD *md, const EVP_MD *mgf1md)
47 int i, emlen = tlen - 1;
48 unsigned char *db, *seed;
49 unsigned char *dbmask = NULL;
50 unsigned char seedmask[EVP_MAX_MD_SIZE];
51 int mdlen, dbmask_len = 0;
58 mdlen = EVP_MD_size(md);
60 if (flen > emlen - 2 * mdlen - 1) {
61 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
62 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
66 if (emlen < 2 * mdlen + 1) {
67 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
68 RSA_R_KEY_SIZE_TOO_SMALL);
76 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
78 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
79 db[emlen - flen - mdlen - 1] = 0x01;
80 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
81 if (RAND_bytes(seed, mdlen) <= 0)
84 dbmask_len = emlen - mdlen;
85 dbmask = OPENSSL_malloc(dbmask_len);
87 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
91 if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
93 for (i = 0; i < dbmask_len; i++)
96 if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
98 for (i = 0; i < mdlen; i++)
99 seed[i] ^= seedmask[i];
103 OPENSSL_cleanse(seedmask, sizeof(seedmask));
104 OPENSSL_clear_free(dbmask, dbmask_len);
108 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
109 const unsigned char *from, int flen, int num,
110 const unsigned char *param, int plen)
112 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
113 param, plen, NULL, NULL);
116 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
117 const unsigned char *from, int flen,
118 int num, const unsigned char *param,
119 int plen, const EVP_MD *md,
120 const EVP_MD *mgf1md)
122 int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
123 unsigned int good, found_one_byte;
124 const unsigned char *maskedseed, *maskeddb;
126 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
127 * Y || maskedSeed || maskedDB
129 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
130 phash[EVP_MAX_MD_SIZE];
138 mdlen = EVP_MD_size(md);
140 if (tlen <= 0 || flen <= 0)
143 * |num| is the length of the modulus; |flen| is the length of the
144 * encoded message. Therefore, for any |from| that was obtained by
145 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
146 * num < 2 * mdlen + 2 must hold for the modulus irrespective of
147 * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
148 * This does not leak any side-channel information.
150 if (num < flen || num < 2 * mdlen + 2)
153 dblen = num - mdlen - 1;
154 db = OPENSSL_malloc(dblen);
156 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
161 em = OPENSSL_zalloc(num);
163 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
164 ERR_R_MALLOC_FAILURE);
169 * Caller is encouraged to pass zero-padded message created with
170 * BN_bn2binpad, but if it doesn't, we do this zero-padding copy
171 * to avoid leaking that information. The copy still leaks some
172 * side-channel information, but it's impossible to have a fixed
173 * memory access pattern since we can't read out of the bounds of
176 memcpy(em + num - flen, from, flen);
181 * The first byte must be zero, however we must not leak if this is
182 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
183 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
185 good = constant_time_is_zero(from[0]);
187 maskedseed = from + 1;
188 maskeddb = from + 1 + mdlen;
190 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
192 for (i = 0; i < mdlen; i++)
193 seed[i] ^= maskedseed[i];
195 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
197 for (i = 0; i < dblen; i++)
198 db[i] ^= maskeddb[i];
200 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
203 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
206 for (i = mdlen; i < dblen; i++) {
208 * Padding consists of a number of 0-bytes, followed by a 1.
210 unsigned int equals1 = constant_time_eq(db[i], 1);
211 unsigned int equals0 = constant_time_is_zero(db[i]);
212 one_index = constant_time_select_int(~found_one_byte & equals1,
214 found_one_byte |= equals1;
215 good &= (found_one_byte | equals0);
218 good &= found_one_byte;
221 * At this point |good| is zero unless the plaintext was valid,
222 * so plaintext-awareness ensures timing side-channels are no longer a
228 msg_index = one_index + 1;
229 mlen = dblen - msg_index;
232 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
235 memcpy(to, db + msg_index, mlen);
241 * To avoid chosen ciphertext attacks, the error message should not
242 * reveal which kind of decoding error happened.
244 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
245 RSA_R_OAEP_DECODING_ERROR);
247 OPENSSL_cleanse(seed, sizeof(seed));
248 OPENSSL_clear_free(db, dblen);
249 OPENSSL_clear_free(em, num);
253 int PKCS1_MGF1(unsigned char *mask, long len,
254 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
257 unsigned char cnt[4];
258 EVP_MD_CTX *c = EVP_MD_CTX_new();
259 unsigned char md[EVP_MAX_MD_SIZE];
265 mdlen = EVP_MD_size(dgst);
268 for (i = 0; outlen < len; i++) {
269 cnt[0] = (unsigned char)((i >> 24) & 255);
270 cnt[1] = (unsigned char)((i >> 16) & 255);
271 cnt[2] = (unsigned char)((i >> 8)) & 255;
272 cnt[3] = (unsigned char)(i & 255);
273 if (!EVP_DigestInit_ex(c, dgst, NULL)
274 || !EVP_DigestUpdate(c, seed, seedlen)
275 || !EVP_DigestUpdate(c, cnt, 4))
277 if (outlen + mdlen <= len) {
278 if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
282 if (!EVP_DigestFinal_ex(c, md, NULL))
284 memcpy(mask + outlen, md, len - outlen);
290 OPENSSL_cleanse(md, sizeof(md));