1 /* $OpenBSD: rsa_oaep.c,v 1.21 2014/07/10 13:58:23 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 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 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, const unsigned char *seed, 33 long seedlen); 34 35 int 36 RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 37 const unsigned char *from, int flen, 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 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 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 51 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 if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL)) 60 return 0; 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, flen); 65 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 66 return 0; 67 68 dbmask = malloc(emlen - SHA_DIGEST_LENGTH); 69 if (dbmask == NULL) { 70 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 71 return 0; 72 } 73 74 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, 75 SHA_DIGEST_LENGTH) < 0) 76 return 0; 77 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 78 db[i] ^= dbmask[i]; 79 80 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, 81 emlen - SHA_DIGEST_LENGTH) < 0) 82 return 0; 83 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 84 seed[i] ^= seedmask[i]; 85 86 free(dbmask); 87 return 1; 88 } 89 90 int 91 RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 92 const unsigned char *from, int flen, int num, const unsigned char *param, 93 int plen) 94 { 95 int i, dblen, mlen = -1; 96 const unsigned char *maskeddb; 97 int lzero; 98 unsigned char *db = NULL; 99 unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 100 unsigned char *padded_from; 101 int bad = 0; 102 103 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 104 /* 105 * 'num' is the length of the modulus, i.e. does not depend 106 * on the particular ciphertext. 107 */ 108 goto decoding_err; 109 110 lzero = num - flen; 111 if (lzero < 0) { 112 /* 113 * signalling this error immediately after detection might allow 114 * for side-channel attacks (e.g. timing if 'plen' is huge 115 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA 116 * Optimal Asymmetric Encryption Padding (OAEP) [...]", 117 * CRYPTO 2001), so we use a 'bad' flag 118 */ 119 bad = 1; 120 lzero = 0; 121 flen = num; /* don't overflow the memcpy to padded_from */ 122 } 123 124 dblen = num - SHA_DIGEST_LENGTH; 125 db = malloc(dblen + num); 126 if (db == NULL) { 127 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, 128 ERR_R_MALLOC_FAILURE); 129 return -1; 130 } 131 132 /* 133 * Always do this zero-padding copy (even when lzero == 0) 134 * to avoid leaking timing info about the value of lzero. 135 */ 136 padded_from = db + dblen; 137 memset(padded_from, 0, lzero); 138 memcpy(padded_from + lzero, from, flen); 139 140 maskeddb = padded_from + SHA_DIGEST_LENGTH; 141 142 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 143 return -1; 144 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 145 seed[i] ^= padded_from[i]; 146 147 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 148 return -1; 149 for (i = 0; i < dblen; i++) 150 db[i] ^= maskeddb[i]; 151 152 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) 153 return -1; 154 155 if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 156 goto decoding_err; 157 else { 158 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 159 if (db[i] != 0x00) 160 break; 161 if (i == dblen || db[i] != 0x01) 162 goto decoding_err; 163 else { 164 /* everything looks OK */ 165 166 mlen = dblen - ++i; 167 if (tlen < mlen) { 168 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, 169 RSA_R_DATA_TOO_LARGE); 170 mlen = -1; 171 } else 172 memcpy(to, db + i, mlen); 173 } 174 } 175 free(db); 176 return mlen; 177 178 decoding_err: 179 /* 180 * To avoid chosen ciphertext attacks, the error message should not 181 * reveal which kind of decoding error happened 182 */ 183 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 184 free(db); 185 return -1; 186 } 187 188 int 189 PKCS1_MGF1(unsigned char *mask, long len, const unsigned char *seed, 190 long seedlen, const EVP_MD *dgst) 191 { 192 long i, outlen = 0; 193 unsigned char cnt[4]; 194 EVP_MD_CTX c; 195 unsigned char md[EVP_MAX_MD_SIZE]; 196 int mdlen; 197 int rv = -1; 198 199 EVP_MD_CTX_init(&c); 200 mdlen = EVP_MD_size(dgst); 201 if (mdlen < 0) 202 goto err; 203 for (i = 0; outlen < len; i++) { 204 cnt[0] = (unsigned char)((i >> 24) & 255); 205 cnt[1] = (unsigned char)((i >> 16) & 255); 206 cnt[2] = (unsigned char)((i >> 8)) & 255; 207 cnt[3] = (unsigned char)(i & 255); 208 if (!EVP_DigestInit_ex(&c, dgst, NULL) || 209 !EVP_DigestUpdate(&c, seed, seedlen) || 210 !EVP_DigestUpdate(&c, cnt, 4)) 211 goto err; 212 if (outlen + mdlen <= len) { 213 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 214 goto err; 215 outlen += mdlen; 216 } else { 217 if (!EVP_DigestFinal_ex(&c, md, NULL)) 218 goto err; 219 memcpy(mask + outlen, md, len - outlen); 220 outlen = len; 221 } 222 } 223 rv = 0; 224 err: 225 EVP_MD_CTX_cleanup(&c); 226 return rv; 227 } 228 229 static int 230 MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen) 231 { 232 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 233 } 234 #endif 235