rsa_oaep.c revision 279265
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 32int 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 MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH); 81 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 82 db[i] ^= dbmask[i]; 83 84 MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH); 85 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 86 seed[i] ^= seedmask[i]; 87 88 OPENSSL_free(dbmask); 89 return 1; 90 } 91 92int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 93 const unsigned char *from, int flen, int num, 94 const unsigned char *param, int plen) 95 { 96 int i, dblen, mlen = -1, one_index = 0, msg_index; 97 unsigned int good, found_one_byte; 98 const unsigned char *maskedseed, *maskeddb; 99 /* |em| is the encoded message, zero-padded to exactly |num| bytes: 100 * em = Y || maskedSeed || maskedDB */ 101 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 102 phash[EVP_MAX_MD_SIZE]; 103 104 if (tlen <= 0 || flen <= 0) 105 return -1; 106 107 /* 108 * |num| is the length of the modulus; |flen| is the length of the 109 * encoded message. Therefore, for any |from| that was obtained by 110 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 111 * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus 112 * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2. 113 * This does not leak any side-channel information. 114 */ 115 if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2) 116 goto decoding_err; 117 118 dblen = num - SHA_DIGEST_LENGTH - 1; 119 db = OPENSSL_malloc(dblen); 120 em = OPENSSL_malloc(num); 121 if (db == NULL || em == NULL) 122 { 123 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 124 goto cleanup; 125 } 126 127 /* 128 * Always do this zero-padding copy (even when num == flen) to avoid 129 * leaking that information. The copy still leaks some side-channel 130 * information, but it's impossible to have a fixed memory access 131 * pattern since we can't read out of the bounds of |from|. 132 * 133 * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL. 134 */ 135 memset(em, 0, num); 136 memcpy(em + num - flen, from, flen); 137 138 /* 139 * The first byte must be zero, however we must not leak if this is 140 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 141 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 142 */ 143 good = constant_time_is_zero(em[0]); 144 145 maskedseed = em + 1; 146 maskeddb = em + 1 + SHA_DIGEST_LENGTH; 147 148 MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen); 149 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 150 seed[i] ^= maskedseed[i]; 151 152 MGF1(db, dblen, seed, SHA_DIGEST_LENGTH); 153 for (i = 0; i < dblen; i++) 154 db[i] ^= maskeddb[i]; 155 156 EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL); 157 158 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH)); 159 160 found_one_byte = 0; 161 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 162 { 163 /* Padding consists of a number of 0-bytes, followed by a 1. */ 164 unsigned int equals1 = constant_time_eq(db[i], 1); 165 unsigned int equals0 = constant_time_is_zero(db[i]); 166 one_index = constant_time_select_int(~found_one_byte & equals1, 167 i, one_index); 168 found_one_byte |= equals1; 169 good &= (found_one_byte | equals0); 170 } 171 172 good &= found_one_byte; 173 174 /* 175 * At this point |good| is zero unless the plaintext was valid, 176 * so plaintext-awareness ensures timing side-channels are no longer a 177 * concern. 178 */ 179 if (!good) 180 goto decoding_err; 181 182 msg_index = one_index + 1; 183 mlen = dblen - msg_index; 184 185 if (tlen < mlen) 186 { 187 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 188 mlen = -1; 189 } 190 else 191 { 192 memcpy(to, db + msg_index, mlen); 193 goto cleanup; 194 } 195 196decoding_err: 197 /* To avoid chosen ciphertext attacks, the error message should not reveal 198 * which kind of decoding error happened. */ 199 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 200cleanup: 201 if (db != NULL) OPENSSL_free(db); 202 if (em != NULL) OPENSSL_free(em); 203 return mlen; 204 } 205 206int PKCS1_MGF1(unsigned char *mask, long len, 207 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 208 { 209 long i, outlen = 0; 210 unsigned char cnt[4]; 211 EVP_MD_CTX c; 212 unsigned char md[EVP_MAX_MD_SIZE]; 213 int mdlen; 214 215 EVP_MD_CTX_init(&c); 216 mdlen = M_EVP_MD_size(dgst); 217 for (i = 0; outlen < len; i++) 218 { 219 cnt[0] = (unsigned char)((i >> 24) & 255); 220 cnt[1] = (unsigned char)((i >> 16) & 255); 221 cnt[2] = (unsigned char)((i >> 8)) & 255; 222 cnt[3] = (unsigned char)(i & 255); 223 EVP_DigestInit_ex(&c,dgst, NULL); 224 EVP_DigestUpdate(&c, seed, seedlen); 225 EVP_DigestUpdate(&c, cnt, 4); 226 if (outlen + mdlen <= len) 227 { 228 EVP_DigestFinal_ex(&c, mask + outlen, NULL); 229 outlen += mdlen; 230 } 231 else 232 { 233 EVP_DigestFinal_ex(&c, md, NULL); 234 memcpy(mask + outlen, md, len - outlen); 235 outlen = len; 236 } 237 } 238 EVP_MD_CTX_cleanup(&c); 239 return 0; 240 } 241 242int MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen) 243 { 244 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 245 } 246#endif 247