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 "constant_time_locl.h"
22 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
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>
31 int MGF1(unsigned char *mask, long len,
32 const unsigned char *seed, long seedlen);
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 int i, emlen = tlen - 1;
39 unsigned char *db, *seed;
40 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
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);
48 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) {
49 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
55 db = to + SHA_DIGEST_LENGTH + 1;
57 EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL);
58 memset(db + SHA_DIGEST_LENGTH, 0,
59 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
60 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
61 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int)flen);
62 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
66 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
70 dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
72 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
76 MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH);
77 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
80 MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH);
81 for (i = 0; i < SHA_DIGEST_LENGTH; i++)
82 seed[i] ^= seedmask[i];
88 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
89 const unsigned char *from, int flen, int num,
90 const unsigned char *param, int plen)
92 int i, dblen, mlen = -1, one_index = 0, msg_index;
93 unsigned int good, found_one_byte;
94 const unsigned char *maskedseed, *maskeddb;
96 * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
97 * Y || maskedSeed || maskedDB
99 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
100 phash[EVP_MAX_MD_SIZE];
102 if (tlen <= 0 || flen <= 0)
106 * |num| is the length of the modulus; |flen| is the length of the
107 * encoded message. Therefore, for any |from| that was obtained by
108 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
109 * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus
110 * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2.
111 * This does not leak any side-channel information.
113 if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2)
116 dblen = num - SHA_DIGEST_LENGTH - 1;
117 db = OPENSSL_malloc(dblen);
118 em = OPENSSL_malloc(num);
119 if (db == NULL || em == NULL) {
120 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
125 * Always do this zero-padding copy (even when num == flen) to avoid
126 * leaking that information. The copy still leaks some side-channel
127 * information, but it's impossible to have a fixed memory access
128 * pattern since we can't read out of the bounds of |from|.
130 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
133 memcpy(em + num - flen, from, flen);
136 * The first byte must be zero, however we must not leak if this is
137 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
138 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
140 good = constant_time_is_zero(em[0]);
143 maskeddb = em + 1 + SHA_DIGEST_LENGTH;
145 MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen);
146 for (i = 0; i < SHA_DIGEST_LENGTH; i++)
147 seed[i] ^= maskedseed[i];
149 MGF1(db, dblen, seed, SHA_DIGEST_LENGTH);
150 for (i = 0; i < dblen; i++)
151 db[i] ^= maskeddb[i];
153 EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL);
156 constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH));
159 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) {
161 * Padding consists of a number of 0-bytes, followed by a 1.
163 unsigned int equals1 = constant_time_eq(db[i], 1);
164 unsigned int equals0 = constant_time_is_zero(db[i]);
165 one_index = constant_time_select_int(~found_one_byte & equals1,
167 found_one_byte |= equals1;
168 good &= (found_one_byte | equals0);
171 good &= found_one_byte;
174 * At this point |good| is zero unless the plaintext was valid,
175 * so plaintext-awareness ensures timing side-channels are no longer a
181 msg_index = one_index + 1;
182 mlen = dblen - msg_index;
185 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
188 memcpy(to, db + msg_index, mlen);
194 * To avoid chosen ciphertext attacks, the error message should not
195 * reveal which kind of decoding error happened.
197 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
206 int PKCS1_MGF1(unsigned char *mask, long len,
207 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
210 unsigned char cnt[4];
212 unsigned char md[EVP_MAX_MD_SIZE];
216 mdlen = M_EVP_MD_size(dgst);
217 for (i = 0; outlen < len; i++) {
218 cnt[0] = (unsigned char)((i >> 24) & 255);
219 cnt[1] = (unsigned char)((i >> 16) & 255);
220 cnt[2] = (unsigned char)((i >> 8)) & 255;
221 cnt[3] = (unsigned char)(i & 255);
222 EVP_DigestInit_ex(&c, dgst, NULL);
223 EVP_DigestUpdate(&c, seed, seedlen);
224 EVP_DigestUpdate(&c, cnt, 4);
225 if (outlen + mdlen <= len) {
226 EVP_DigestFinal_ex(&c, mask + outlen, NULL);
229 EVP_DigestFinal_ex(&c, md, NULL);
230 memcpy(mask + outlen, md, len - outlen);
234 EVP_MD_CTX_cleanup(&c);
238 int MGF1(unsigned char *mask, long len, const unsigned char *seed,
241 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());