1 /* $OpenBSD: rsa_oaep.c,v 1.23 2014/07/11 08:44:49 jsing 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. */ 4 5 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ 6 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. 11 * 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. 19 */ 20 21 #include <stdio.h> 22 #include <string.h> 23 24 #include <openssl/opensslconf.h> 25 26 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 27 28 #include <openssl/bn.h> 29 #include <openssl/err.h> 30 #include <openssl/evp.h> 31 #include <openssl/rand.h> 32 #include <openssl/rsa.h> 33 #include <openssl/sha.h> 34 35 static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 36 long seedlen); 37 38 int 39 RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 40 const unsigned char *from, int flen, const unsigned char *param, int plen) 41 { 42 int i, emlen = tlen - 1; 43 unsigned char *db, *seed; 44 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH]; 45 46 if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) { 47 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 48 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 49 return 0; 50 } 51 52 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) { 53 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 54 RSA_R_KEY_SIZE_TOO_SMALL); 55 return 0; 56 } 57 58 to[0] = 0; 59 seed = to + 1; 60 db = to + SHA_DIGEST_LENGTH + 1; 61 62 if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL)) 63 return 0; 64 memset(db + SHA_DIGEST_LENGTH, 0, 65 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1); 66 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01; 67 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, flen); 68 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 69 return 0; 70 71 dbmask = malloc(emlen - SHA_DIGEST_LENGTH); 72 if (dbmask == NULL) { 73 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 74 return 0; 75 } 76 77 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, 78 SHA_DIGEST_LENGTH) < 0) 79 return 0; 80 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 81 db[i] ^= dbmask[i]; 82 83 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, 84 emlen - SHA_DIGEST_LENGTH) < 0) 85 return 0; 86 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 87 seed[i] ^= seedmask[i]; 88 89 free(dbmask); 90 return 1; 91 } 92 93 int 94 RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 95 const unsigned char *from, int flen, int num, const unsigned char *param, 96 int plen) 97 { 98 int i, dblen, mlen = -1; 99 const unsigned char *maskeddb; 100 int lzero; 101 unsigned char *db = NULL; 102 unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 103 unsigned char *padded_from; 104 int bad = 0; 105 106 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 107 /* 108 * 'num' is the length of the modulus, i.e. does not depend 109 * on the particular ciphertext. 110 */ 111 goto decoding_err; 112 113 lzero = num - flen; 114 if (lzero < 0) { 115 /* 116 * signalling this error immediately after detection might allow 117 * for side-channel attacks (e.g. timing if 'plen' is huge 118 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA 119 * Optimal Asymmetric Encryption Padding (OAEP) [...]", 120 * CRYPTO 2001), so we use a 'bad' flag 121 */ 122 bad = 1; 123 lzero = 0; 124 flen = num; /* don't overflow the memcpy to padded_from */ 125 } 126 127 dblen = num - SHA_DIGEST_LENGTH; 128 db = malloc(dblen + num); 129 if (db == NULL) { 130 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, 131 ERR_R_MALLOC_FAILURE); 132 return -1; 133 } 134 135 /* 136 * Always do this zero-padding copy (even when lzero == 0) 137 * to avoid leaking timing info about the value of lzero. 138 */ 139 padded_from = db + dblen; 140 memset(padded_from, 0, lzero); 141 memcpy(padded_from + lzero, from, flen); 142 143 maskeddb = padded_from + SHA_DIGEST_LENGTH; 144 145 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 146 return -1; 147 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 148 seed[i] ^= padded_from[i]; 149 150 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 151 return -1; 152 for (i = 0; i < dblen; i++) 153 db[i] ^= maskeddb[i]; 154 155 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) 156 return -1; 157 158 if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 159 goto decoding_err; 160 else { 161 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 162 if (db[i] != 0x00) 163 break; 164 if (i == dblen || db[i] != 0x01) 165 goto decoding_err; 166 else { 167 /* everything looks OK */ 168 169 mlen = dblen - ++i; 170 if (tlen < mlen) { 171 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, 172 RSA_R_DATA_TOO_LARGE); 173 mlen = -1; 174 } else 175 memcpy(to, db + i, mlen); 176 } 177 } 178 free(db); 179 return mlen; 180 181 decoding_err: 182 /* 183 * To avoid chosen ciphertext attacks, the error message should not 184 * reveal which kind of decoding error happened 185 */ 186 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 187 free(db); 188 return -1; 189 } 190 191 int 192 PKCS1_MGF1(unsigned char *mask, long len, const unsigned char *seed, 193 long seedlen, const EVP_MD *dgst) 194 { 195 long i, outlen = 0; 196 unsigned char cnt[4]; 197 EVP_MD_CTX c; 198 unsigned char md[EVP_MAX_MD_SIZE]; 199 int mdlen; 200 int rv = -1; 201 202 EVP_MD_CTX_init(&c); 203 mdlen = EVP_MD_size(dgst); 204 if (mdlen < 0) 205 goto err; 206 for (i = 0; outlen < len; i++) { 207 cnt[0] = (unsigned char)((i >> 24) & 255); 208 cnt[1] = (unsigned char)((i >> 16) & 255); 209 cnt[2] = (unsigned char)((i >> 8)) & 255; 210 cnt[3] = (unsigned char)(i & 255); 211 if (!EVP_DigestInit_ex(&c, dgst, NULL) || 212 !EVP_DigestUpdate(&c, seed, seedlen) || 213 !EVP_DigestUpdate(&c, cnt, 4)) 214 goto err; 215 if (outlen + mdlen <= len) { 216 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 217 goto err; 218 outlen += mdlen; 219 } else { 220 if (!EVP_DigestFinal_ex(&c, md, NULL)) 221 goto err; 222 memcpy(mask + outlen, md, len - outlen); 223 outlen = len; 224 } 225 } 226 rv = 0; 227 err: 228 EVP_MD_CTX_cleanup(&c); 229 return rv; 230 } 231 232 static int 233 MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen) 234 { 235 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 236 } 237 #endif 238