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 22 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 23 #include <stdio.h> 24 #include "cryptlib.h" 25 #include <openssl/bn.h> 26 #include <openssl/rsa.h> 27 #include <openssl/evp.h> 28 #include <openssl/rand.h> 29 #include <openssl/sha.h> 30 31 static int MGF1(unsigned char *mask, long len, 32 const unsigned char *seed, long seedlen); 33 34 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 35 const unsigned char *from, int flen, 36 const unsigned char *param, int plen) 37 { 38 int i, emlen = tlen - 1; 39 unsigned char *db, *seed; 40 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH]; 41 42 if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) 43 { 44 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 45 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 46 return 0; 47 } 48 49 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) 50 { 51 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL); 52 return 0; 53 } 54 55 to[0] = 0; 56 seed = to + 1; 57 db = to + SHA_DIGEST_LENGTH + 1; 58 59 EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL); 60 memset(db + SHA_DIGEST_LENGTH, 0, 61 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1); 62 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01; 63 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen); 64 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 65 return 0; 66 #ifdef PKCS_TESTVECT 67 memcpy(seed, 68 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 69 20); 70 #endif 71 72 dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH); 73 if (dbmask == NULL) 74 { 75 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 76 return 0; 77 } 78 79 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0) 80 return 0; 81 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 82 db[i] ^= dbmask[i]; 83 84 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0) 85 return 0; 86 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 87 seed[i] ^= seedmask[i]; 88 89 OPENSSL_free(dbmask); 90 return 1; 91 } 92 93 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 94 const unsigned char *from, int flen, int num, 95 const unsigned char *param, int plen) 96 { 97 int i, dblen, mlen = -1; 98 const unsigned char *maskeddb; 99 int lzero; 100 unsigned char *db = NULL, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 101 unsigned char *padded_from; 102 int bad = 0; 103 104 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 105 /* 'num' is the length of the modulus, i.e. does not depend on the 106 * particular ciphertext. */ 107 goto decoding_err; 108 109 lzero = num - flen; 110 if (lzero < 0) 111 { 112 /* signalling this error immediately after detection might allow 113 * for side-channel attacks (e.g. timing if 'plen' is huge 114 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA Optimal 115 * Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001), 116 * so we use a 'bad' flag */ 117 bad = 1; 118 lzero = 0; 119 flen = num; /* don't overflow the memcpy to padded_from */ 120 } 121 122 dblen = num - SHA_DIGEST_LENGTH; 123 db = OPENSSL_malloc(dblen + num); 124 if (db == NULL) 125 { 126 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 127 return -1; 128 } 129 130 /* Always do this zero-padding copy (even when lzero == 0) 131 * to avoid leaking timing info about the value of lzero. */ 132 padded_from = db + dblen; 133 memset(padded_from, 0, lzero); 134 memcpy(padded_from + lzero, from, flen); 135 136 maskeddb = padded_from + SHA_DIGEST_LENGTH; 137 138 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 139 return -1; 140 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 141 seed[i] ^= padded_from[i]; 142 143 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 144 return -1; 145 for (i = 0; i < dblen; i++) 146 db[i] ^= maskeddb[i]; 147 148 EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL); 149 150 if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 151 goto decoding_err; 152 else 153 { 154 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 155 if (db[i] != 0x00) 156 break; 157 if (i == dblen || db[i] != 0x01) 158 goto decoding_err; 159 else 160 { 161 /* everything looks OK */ 162 163 mlen = dblen - ++i; 164 if (tlen < mlen) 165 { 166 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 167 mlen = -1; 168 } 169 else 170 memcpy(to, db + i, mlen); 171 } 172 } 173 OPENSSL_free(db); 174 return mlen; 175 176 decoding_err: 177 /* to avoid chosen ciphertext attacks, the error message should not reveal 178 * which kind of decoding error happened */ 179 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 180 if (db != NULL) OPENSSL_free(db); 181 return -1; 182 } 183 184 int PKCS1_MGF1(unsigned char *mask, long len, 185 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 186 { 187 long i, outlen = 0; 188 unsigned char cnt[4]; 189 EVP_MD_CTX c; 190 unsigned char md[EVP_MAX_MD_SIZE]; 191 int mdlen; 192 193 EVP_MD_CTX_init(&c); 194 mdlen = EVP_MD_size(dgst); 195 if (mdlen < 0) 196 return -1; 197 for (i = 0; outlen < len; i++) 198 { 199 cnt[0] = (unsigned char)((i >> 24) & 255); 200 cnt[1] = (unsigned char)((i >> 16) & 255); 201 cnt[2] = (unsigned char)((i >> 8)) & 255; 202 cnt[3] = (unsigned char)(i & 255); 203 EVP_DigestInit_ex(&c,dgst, NULL); 204 EVP_DigestUpdate(&c, seed, seedlen); 205 EVP_DigestUpdate(&c, cnt, 4); 206 if (outlen + mdlen <= len) 207 { 208 EVP_DigestFinal_ex(&c, mask + outlen, NULL); 209 outlen += mdlen; 210 } 211 else 212 { 213 EVP_DigestFinal_ex(&c, md, NULL); 214 memcpy(mask + outlen, md, len - outlen); 215 outlen = len; 216 } 217 } 218 EVP_MD_CTX_cleanup(&c); 219 return 0; 220 } 221 222 static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 223 long seedlen) 224 { 225 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 226 } 227 #endif 228
