1 /* $OpenBSD: rsa_oaep.c,v 1.29 2018/08/19 20:17:20 tb Exp $ */
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.
25 #include <openssl/opensslconf.h>
27 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
29 #include <openssl/bn.h>
30 #include <openssl/err.h>
31 #include <openssl/evp.h>
32 #include <openssl/rsa.h>
33 #include <openssl/sha.h>
35 static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
39 RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
40 const unsigned char *from, int flen, const unsigned char *param, int plen)
42 int i, emlen = tlen - 1;
43 unsigned char *db, *seed;
44 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
46 if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) {
47 RSAerror(RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
51 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) {
52 RSAerror(RSA_R_KEY_SIZE_TOO_SMALL);
58 db = to + SHA_DIGEST_LENGTH + 1;
60 if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
62 memset(db + SHA_DIGEST_LENGTH, 0,
63 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
64 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
65 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, flen);
66 arc4random_buf(seed, SHA_DIGEST_LENGTH);
68 dbmask = malloc(emlen - SHA_DIGEST_LENGTH);
70 RSAerror(ERR_R_MALLOC_FAILURE);
74 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed,
75 SHA_DIGEST_LENGTH) < 0) {
79 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
82 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db,
83 emlen - SHA_DIGEST_LENGTH) < 0) {
87 for (i = 0; i < SHA_DIGEST_LENGTH; i++)
88 seed[i] ^= seedmask[i];
95 RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
96 const unsigned char *from, int flen, int num, const unsigned char *param,
99 int i, dblen, mlen = -1;
100 const unsigned char *maskeddb;
102 unsigned char *db = NULL;
103 unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
104 unsigned char *padded_from;
107 if (--num < 2 * SHA_DIGEST_LENGTH + 1)
109 * 'num' is the length of the modulus, i.e. does not depend
110 * on the particular ciphertext.
117 * signalling this error immediately after detection might allow
118 * for side-channel attacks (e.g. timing if 'plen' is huge
119 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA
120 * Optimal Asymmetric Encryption Padding (OAEP) [...]",
121 * CRYPTO 2001), so we use a 'bad' flag
125 flen = num; /* don't overflow the memcpy to padded_from */
128 dblen = num - SHA_DIGEST_LENGTH;
129 if ((db = malloc(dblen + num)) == NULL) {
130 RSAerror(ERR_R_MALLOC_FAILURE);
135 * Always do this zero-padding copy (even when lzero == 0)
136 * to avoid leaking timing info about the value of lzero.
138 padded_from = db + dblen;
139 memset(padded_from, 0, lzero);
140 memcpy(padded_from + lzero, from, flen);
142 maskeddb = padded_from + SHA_DIGEST_LENGTH;
144 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
146 for (i = 0; i < SHA_DIGEST_LENGTH; i++)
147 seed[i] ^= padded_from[i];
149 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
151 for (i = 0; i < dblen; i++)
152 db[i] ^= maskeddb[i];
154 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
157 if (timingsafe_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
160 for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
163 if (i == dblen || db[i] != 0x01)
166 /* everything looks OK */
170 RSAerror(RSA_R_DATA_TOO_LARGE);
173 memcpy(to, db + i, mlen);
181 * To avoid chosen ciphertext attacks, the error message should not
182 * reveal which kind of decoding error happened
184 RSAerror(RSA_R_OAEP_DECODING_ERROR);
191 PKCS1_MGF1(unsigned char *mask, long len, const unsigned char *seed,
192 long seedlen, const EVP_MD *dgst)
195 unsigned char cnt[4];
197 unsigned char md[EVP_MAX_MD_SIZE];
202 mdlen = EVP_MD_size(dgst);
205 for (i = 0; outlen < len; i++) {
206 cnt[0] = (unsigned char)((i >> 24) & 255);
207 cnt[1] = (unsigned char)((i >> 16) & 255);
208 cnt[2] = (unsigned char)((i >> 8)) & 255;
209 cnt[3] = (unsigned char)(i & 255);
210 if (!EVP_DigestInit_ex(&c, dgst, NULL) ||
211 !EVP_DigestUpdate(&c, seed, seedlen) ||
212 !EVP_DigestUpdate(&c, cnt, 4))
214 if (outlen + mdlen <= len) {
215 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
219 if (!EVP_DigestFinal_ex(&c, md, NULL))
221 memcpy(mask + outlen, md, len - outlen);
227 EVP_MD_CTX_cleanup(&c);
232 MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen)
234 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());