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. */ 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 "constant_time_locl.h" 22 23 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 24 #include <stdio.h> 25 #include "cryptlib.h" 26 #include <openssl/bn.h> 27 #include <openssl/rsa.h> 28 #include <openssl/evp.h> 29 #include <openssl/rand.h> 30 #include <openssl/sha.h> 31 32 static int MGF1(unsigned char *mask, long len, 33 const unsigned char *seed, long seedlen); 34 35 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 36 const unsigned char *from, int flen, 37 const unsigned char *param, int plen) 38 { 39 int i, emlen = tlen - 1; 40 unsigned char *db, *seed; 41 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH]; 42 43 if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) 44 { 45 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 46 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 47 return 0; 48 } 49 50 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) 51 { 52 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL); 53 return 0; 54 } 55 56 to[0] = 0; 57 seed = to + 1; 58 db = to + SHA_DIGEST_LENGTH + 1; 59 60 if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL)) 61 return 0; 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, (unsigned int) flen); 66 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 67 return 0; 68 #ifdef PKCS_TESTVECT 69 memcpy(seed, 70 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 71 20); 72 #endif 73 74 dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH); 75 if (dbmask == NULL) 76 { 77 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 78 return 0; 79 } 80 81 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0) 82 return 0; 83 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 84 db[i] ^= dbmask[i]; 85 86 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0) 87 return 0; 88 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 89 seed[i] ^= seedmask[i]; 90 91 OPENSSL_free(dbmask); 92 return 1; 93 } 94 95 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 96 const unsigned char *from, int flen, int num, 97 const unsigned char *param, int plen) 98 { 99 int i, dblen, mlen = -1, one_index = 0, msg_index; 100 unsigned int good, found_one_byte; 101 const unsigned char *maskedseed, *maskeddb; 102 /* |em| is the encoded message, zero-padded to exactly |num| bytes: 103 * em = Y || maskedSeed || maskedDB */ 104 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 105 phash[EVP_MAX_MD_SIZE]; 106 107 if (tlen <= 0 || flen <= 0) 108 return -1; 109 110 /* 111 * |num| is the length of the modulus; |flen| is the length of the 112 * encoded message. Therefore, for any |from| that was obtained by 113 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 114 * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus 115 * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2. 116 * This does not leak any side-channel information. 117 */ 118 if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2) 119 goto decoding_err; 120 121 dblen = num - SHA_DIGEST_LENGTH - 1; 122 db = OPENSSL_malloc(dblen); 123 em = OPENSSL_malloc(num); 124 if (db == NULL || em == NULL) 125 { 126 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 127 goto cleanup; 128 } 129 130 /* 131 * Always do this zero-padding copy (even when num == flen) to avoid 132 * leaking that information. The copy still leaks some side-channel 133 * information, but it's impossible to have a fixed memory access 134 * pattern since we can't read out of the bounds of |from|. 135 * 136 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL. 137 */ 138 memset(em, 0, num); 139 memcpy(em + num - flen, from, flen); 140 141 /* 142 * The first byte must be zero, however we must not leak if this is 143 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 144 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 145 */ 146 good = constant_time_is_zero(em[0]); 147 148 maskedseed = em + 1; 149 maskeddb = em + 1 + SHA_DIGEST_LENGTH; 150 151 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 152 goto cleanup; 153 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 154 seed[i] ^= maskedseed[i]; 155 156 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 157 goto cleanup; 158 for (i = 0; i < dblen; i++) 159 db[i] ^= maskeddb[i]; 160 161 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) 162 goto cleanup; 163 164 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH)); 165 166 found_one_byte = 0; 167 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 168 { 169 /* Padding consists of a number of 0-bytes, followed by a 1. */ 170 unsigned int equals1 = constant_time_eq(db[i], 1); 171 unsigned int equals0 = constant_time_is_zero(db[i]); 172 one_index = constant_time_select_int(~found_one_byte & equals1, 173 i, one_index); 174 found_one_byte |= equals1; 175 good &= (found_one_byte | equals0); 176 } 177 178 good &= found_one_byte; 179 180 /* 181 * At this point |good| is zero unless the plaintext was valid, 182 * so plaintext-awareness ensures timing side-channels are no longer a 183 * concern. 184 */ 185 if (!good) 186 goto decoding_err; 187 188 msg_index = one_index + 1; 189 mlen = dblen - msg_index; 190 191 if (tlen < mlen) 192 { 193 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 194 mlen = -1; 195 } 196 else 197 { 198 memcpy(to, db + msg_index, mlen); 199 goto cleanup; 200 } 201 202 decoding_err: 203 /* To avoid chosen ciphertext attacks, the error message should not reveal 204 * which kind of decoding error happened. */ 205 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 206 cleanup: 207 if (db != NULL) OPENSSL_free(db); 208 if (em != NULL) OPENSSL_free(em); 209 return mlen; 210 } 211 212 int PKCS1_MGF1(unsigned char *mask, long len, 213 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 214 { 215 long i, outlen = 0; 216 unsigned char cnt[4]; 217 EVP_MD_CTX c; 218 unsigned char md[EVP_MAX_MD_SIZE]; 219 int mdlen; 220 int rv = -1; 221 222 EVP_MD_CTX_init(&c); 223 mdlen = EVP_MD_size(dgst); 224 if (mdlen < 0) 225 goto err; 226 for (i = 0; outlen < len; i++) 227 { 228 cnt[0] = (unsigned char)((i >> 24) & 255); 229 cnt[1] = (unsigned char)((i >> 16) & 255); 230 cnt[2] = (unsigned char)((i >> 8)) & 255; 231 cnt[3] = (unsigned char)(i & 255); 232 if (!EVP_DigestInit_ex(&c,dgst, NULL) 233 || !EVP_DigestUpdate(&c, seed, seedlen) 234 || !EVP_DigestUpdate(&c, cnt, 4)) 235 goto err; 236 if (outlen + mdlen <= len) 237 { 238 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 239 goto err; 240 outlen += mdlen; 241 } 242 else 243 { 244 if (!EVP_DigestFinal_ex(&c, md, NULL)) 245 goto err; 246 memcpy(mask + outlen, md, len - outlen); 247 outlen = len; 248 } 249 } 250 rv = 0; 251 err: 252 EVP_MD_CTX_cleanup(&c); 253 return rv; 254 } 255 256 static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 257 long seedlen) 258 { 259 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 260 } 261 #endif 262
