1 /* crypto/rsa/rsa_oaep.c */
2 /* Written by Ulf Moeller. This software is distributed on an "AS IS"
3 basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. */
5 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
7 /* See Victor Shoup, "OAEP reconsidered," Nov. 2000,
8 * <URL: http://www.shoup.net/papers/oaep.ps.Z>
9 * for problems with the security proof for the
10 * original OAEP scheme, which EME-OAEP is based on.
12 * A new proof can be found in E. Fujisaki, T. Okamoto,
13 * D. Pointcheval, J. Stern, "RSA-OEAP is Still Alive!",
14 * Dec. 2000, <URL: http://eprint.iacr.org/2000/061/>.
15 * The new proof has stronger requirements for the
16 * underlying permutation: "partial-one-wayness" instead
17 * of one-wayness. For the RSA function, this is
18 * an equivalent notion.
23 #include "constant_time_locl.h"
25 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
28 #include <openssl/bn.h>
29 #include <openssl/rsa.h>
30 #include <openssl/evp.h>
31 #include <openssl/rand.h>
32 #include <openssl/sha.h>
34 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
35 const unsigned char *from, int flen,
36 const unsigned char *param, int plen)
38 return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
39 param, plen, NULL, NULL);
42 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
43 const unsigned char *from, int flen,
44 const unsigned char *param, int plen,
45 const EVP_MD *md, const EVP_MD *mgf1md)
47 int i, emlen = tlen - 1;
48 unsigned char *db, *seed;
49 unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
57 mdlen = EVP_MD_size(md);
59 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)
68 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, RSA_R_KEY_SIZE_TOO_SMALL);
76 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
79 emlen - flen - 2 * mdlen - 1);
80 db[emlen - flen - mdlen - 1] = 0x01;
81 memcpy(db + emlen - flen - mdlen, from, (unsigned int) flen);
82 if (RAND_bytes(seed, mdlen) <= 0)
86 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
90 dbmask = OPENSSL_malloc(emlen - mdlen);
93 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
97 if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
99 for (i = 0; i < emlen - mdlen; i++)
102 if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
104 for (i = 0; i < mdlen; i++)
105 seed[i] ^= seedmask[i];
107 OPENSSL_free(dbmask);
111 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
112 const unsigned char *from, int flen, int num,
113 const unsigned char *param, int plen)
115 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from , flen, num,
120 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
121 const unsigned char *from, int flen, int num,
122 const unsigned char *param, int plen,
123 const EVP_MD *md, const EVP_MD *mgf1md)
125 int i, dblen, mlen = -1, one_index = 0, msg_index;
126 unsigned int good, found_one_byte;
127 const unsigned char *maskedseed, *maskeddb;
128 /* |em| is the encoded message, zero-padded to exactly |num| bytes:
129 * em = Y || maskedSeed || maskedDB */
130 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
131 phash[EVP_MAX_MD_SIZE];
139 mdlen = EVP_MD_size(md);
141 if (tlen <= 0 || flen <= 0)
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.
151 if (num < flen || num < 2 * mdlen + 2)
154 dblen = num - mdlen - 1;
155 db = OPENSSL_malloc(dblen);
156 em = OPENSSL_malloc(num);
157 if (db == NULL || em == NULL)
159 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
164 * Always do this zero-padding copy (even when num == flen) to avoid
165 * leaking that information. The copy still leaks some side-channel
166 * information, but it's impossible to have a fixed memory access
167 * pattern since we can't read out of the bounds of |from|.
169 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
172 memcpy(em + num - flen, from, flen);
175 * The first byte must be zero, however we must not leak if this is
176 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
177 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
179 good = constant_time_is_zero(em[0]);
182 maskeddb = em + 1 + mdlen;
184 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
186 for (i = 0; i < mdlen; i++)
187 seed[i] ^= maskedseed[i];
189 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
191 for (i = 0; i < dblen; i++)
192 db[i] ^= maskeddb[i];
194 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
197 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
200 for (i = mdlen; i < dblen; i++)
202 /* Padding consists of a number of 0-bytes, followed by a 1. */
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,
207 found_one_byte |= equals1;
208 good &= (found_one_byte | equals0);
211 good &= found_one_byte;
214 * At this point |good| is zero unless the plaintext was valid,
215 * so plaintext-awareness ensures timing side-channels are no longer a
221 msg_index = one_index + 1;
222 mlen = dblen - msg_index;
226 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
231 memcpy(to, db + msg_index, mlen);
236 /* To avoid chosen ciphertext attacks, the error message should not reveal
237 * which kind of decoding error happened. */
238 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_OAEP_DECODING_ERROR);
240 if (db != NULL) OPENSSL_free(db);
241 if (em != NULL) OPENSSL_free(em);
245 int PKCS1_MGF1(unsigned char *mask, long len,
246 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
249 unsigned char cnt[4];
251 unsigned char md[EVP_MAX_MD_SIZE];
256 mdlen = M_EVP_MD_size(dgst);
259 for (i = 0; outlen < len; i++)
261 cnt[0] = (unsigned char)((i >> 24) & 255);
262 cnt[1] = (unsigned char)((i >> 16) & 255);
263 cnt[2] = (unsigned char)((i >> 8)) & 255;
264 cnt[3] = (unsigned char)(i & 255);
265 if (!EVP_DigestInit_ex(&c,dgst, NULL)
266 || !EVP_DigestUpdate(&c, seed, seedlen)
267 || !EVP_DigestUpdate(&c, cnt, 4))
269 if (outlen + mdlen <= len)
271 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
277 if (!EVP_DigestFinal_ex(&c, md, NULL))
279 memcpy(mask + outlen, md, len - outlen);
285 EVP_MD_CTX_cleanup(&c);