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 32static int MGF1(unsigned char *mask, long len, 33 const unsigned char *seed, long seedlen); 34 35int 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 EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL); 61 memset(db + SHA_DIGEST_LENGTH, 0, 62 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1); 63 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01; 64 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen); 65 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 66 return 0; 67#ifdef PKCS_TESTVECT 68 memcpy(seed, 69 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 70 20); 71#endif 72 73 dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH); 74 if (dbmask == NULL) 75 { 76 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 77 return 0; 78 } 79 80 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0) 81 return 0; 82 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 83 db[i] ^= dbmask[i]; 84 85 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0) 86 return 0; 87 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 88 seed[i] ^= seedmask[i]; 89 90 OPENSSL_free(dbmask); 91 return 1; 92 } 93 94int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 95 const unsigned char *from, int flen, int num, 96 const unsigned char *param, int plen) 97 { 98 int i, dblen, mlen = -1, one_index = 0, msg_index; 99 unsigned int good, found_one_byte; 100 const unsigned char *maskedseed, *maskeddb; 101 /* |em| is the encoded message, zero-padded to exactly |num| bytes: 102 * em = Y || maskedSeed || maskedDB */ 103 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 104 phash[EVP_MAX_MD_SIZE]; 105 106 if (tlen <= 0 || flen <= 0) 107 return -1; 108 109 /* 110 * |num| is the length of the modulus; |flen| is the length of the 111 * encoded message. Therefore, for any |from| that was obtained by 112 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 113 * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus 114 * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2. 115 * This does not leak any side-channel information. 116 */ 117 if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2) 118 goto decoding_err; 119 120 dblen = num - SHA_DIGEST_LENGTH - 1; 121 db = OPENSSL_malloc(dblen); 122 em = OPENSSL_malloc(num); 123 if (db == NULL || em == NULL) 124 { 125 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 126 goto cleanup; 127 } 128 129 /* 130 * Always do this zero-padding copy (even when num == flen) to avoid 131 * leaking that information. The copy still leaks some side-channel 132 * information, but it's impossible to have a fixed memory access 133 * pattern since we can't read out of the bounds of |from|. 134 * 135 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL. 136 */ 137 memset(em, 0, num); 138 memcpy(em + num - flen, from, flen); 139 140 /* 141 * The first byte must be zero, however we must not leak if this is 142 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 143 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 144 */ 145 good = constant_time_is_zero(em[0]); 146 147 maskedseed = em + 1; 148 maskeddb = em + 1 + SHA_DIGEST_LENGTH; 149 150 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 151 goto cleanup; 152 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 153 seed[i] ^= maskedseed[i]; 154 155 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 156 goto cleanup; 157 for (i = 0; i < dblen; i++) 158 db[i] ^= maskeddb[i]; 159 160 EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL); 161 162 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH)); 163 164 found_one_byte = 0; 165 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 166 { 167 /* Padding consists of a number of 0-bytes, followed by a 1. */ 168 unsigned int equals1 = constant_time_eq(db[i], 1); 169 unsigned int equals0 = constant_time_is_zero(db[i]); 170 one_index = constant_time_select_int(~found_one_byte & equals1, 171 i, one_index); 172 found_one_byte |= equals1; 173 good &= (found_one_byte | equals0); 174 } 175 176 good &= found_one_byte; 177 178 /* 179 * At this point |good| is zero unless the plaintext was valid, 180 * so plaintext-awareness ensures timing side-channels are no longer a 181 * concern. 182 */ 183 if (!good) 184 goto decoding_err; 185 186 msg_index = one_index + 1; 187 mlen = dblen - msg_index; 188 189 if (tlen < mlen) 190 { 191 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 192 mlen = -1; 193 } 194 else 195 { 196 memcpy(to, db + msg_index, mlen); 197 goto cleanup; 198 } 199 200decoding_err: 201 /* To avoid chosen ciphertext attacks, the error message should not reveal 202 * which kind of decoding error happened. */ 203 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 204cleanup: 205 if (db != NULL) OPENSSL_free(db); 206 if (em != NULL) OPENSSL_free(em); 207 return mlen; 208 } 209 210int PKCS1_MGF1(unsigned char *mask, long len, 211 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 212 { 213 long i, outlen = 0; 214 unsigned char cnt[4]; 215 EVP_MD_CTX c; 216 unsigned char md[EVP_MAX_MD_SIZE]; 217 int mdlen; 218 int rv = -1; 219 220 EVP_MD_CTX_init(&c); 221 mdlen = EVP_MD_size(dgst); 222 if (mdlen < 0) 223 goto err; 224 for (i = 0; outlen < len; i++) 225 { 226 cnt[0] = (unsigned char)((i >> 24) & 255); 227 cnt[1] = (unsigned char)((i >> 16) & 255); 228 cnt[2] = (unsigned char)((i >> 8)) & 255; 229 cnt[3] = (unsigned char)(i & 255); 230 if (!EVP_DigestInit_ex(&c,dgst, NULL) 231 || !EVP_DigestUpdate(&c, seed, seedlen) 232 || !EVP_DigestUpdate(&c, cnt, 4)) 233 goto err; 234 if (outlen + mdlen <= len) 235 { 236 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 237 goto err; 238 outlen += mdlen; 239 } 240 else 241 { 242 if (!EVP_DigestFinal_ex(&c, md, NULL)) 243 goto err; 244 memcpy(mask + outlen, md, len - outlen); 245 outlen = len; 246 } 247 } 248 rv = 0; 249 err: 250 EVP_MD_CTX_cleanup(&c); 251 return rv; 252 } 253 254static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 255 long seedlen) 256 { 257 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 258 } 259#endif 260