1 /* $OpenBSD: rsa_oaep.c,v 1.29 2018/08/19 20:17:20 tb 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 <stdlib.h> 23 #include <string.h> 24 25 #include <openssl/opensslconf.h> 26 27 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 28 29 #include <openssl/bn.h> 30 #include <openssl/err.h> 31 #include <openssl/evp.h> 32 #include <openssl/rsa.h> 33 #include <openssl/sha.h> 34 35 static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 36 long seedlen); 37 38 int 39 RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 40 const unsigned char *from, int flen, const unsigned char *param, int plen) 41 { 42 int i, emlen = tlen - 1; 43 unsigned char *db, *seed; 44 unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH]; 45 46 if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) { 47 RSAerror(RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 48 return 0; 49 } 50 51 if (emlen < 2 * SHA_DIGEST_LENGTH + 1) { 52 RSAerror(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, flen); 66 arc4random_buf(seed, SHA_DIGEST_LENGTH); 67 68 dbmask = malloc(emlen - SHA_DIGEST_LENGTH); 69 if (dbmask == NULL) { 70 RSAerror(ERR_R_MALLOC_FAILURE); 71 return 0; 72 } 73 74 if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, 75 SHA_DIGEST_LENGTH) < 0) { 76 free(dbmask); 77 return 0; 78 } 79 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 80 db[i] ^= dbmask[i]; 81 82 if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, 83 emlen - SHA_DIGEST_LENGTH) < 0) { 84 free(dbmask); 85 return 0; 86 } 87 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 88 seed[i] ^= seedmask[i]; 89 90 free(dbmask); 91 return 1; 92 } 93 94 int 95 RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 96 const unsigned char *from, int flen, int num, const unsigned char *param, 97 int plen) 98 { 99 int i, dblen, mlen = -1; 100 const unsigned char *maskeddb; 101 int lzero; 102 unsigned char *db = NULL; 103 unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 104 unsigned char *padded_from; 105 int bad = 0; 106 107 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 108 /* 109 * 'num' is the length of the modulus, i.e. does not depend 110 * on the particular ciphertext. 111 */ 112 goto decoding_err; 113 114 lzero = num - flen; 115 if (lzero < 0) { 116 /* 117 * signalling this error immediately after detection might allow 118 * for side-channel attacks (e.g. timing if 'plen' is huge 119 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA 120 * Optimal Asymmetric Encryption Padding (OAEP) [...]", 121 * CRYPTO 2001), so we use a 'bad' flag 122 */ 123 bad = 1; 124 lzero = 0; 125 flen = num; /* don't overflow the memcpy to padded_from */ 126 } 127 128 dblen = num - SHA_DIGEST_LENGTH; 129 if ((db = malloc(dblen + num)) == NULL) { 130 RSAerror(ERR_R_MALLOC_FAILURE); 131 return -1; 132 } 133 134 /* 135 * Always do this zero-padding copy (even when lzero == 0) 136 * to avoid leaking timing info about the value of lzero. 137 */ 138 padded_from = db + dblen; 139 memset(padded_from, 0, lzero); 140 memcpy(padded_from + lzero, from, flen); 141 142 maskeddb = padded_from + SHA_DIGEST_LENGTH; 143 144 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 145 goto err; 146 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 147 seed[i] ^= padded_from[i]; 148 149 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 150 goto err; 151 for (i = 0; i < dblen; i++) 152 db[i] ^= maskeddb[i]; 153 154 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) 155 goto err; 156 157 if (timingsafe_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 158 goto decoding_err; 159 else { 160 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 161 if (db[i] != 0x00) 162 break; 163 if (i == dblen || db[i] != 0x01) 164 goto decoding_err; 165 else { 166 /* everything looks OK */ 167 168 mlen = dblen - ++i; 169 if (tlen < mlen) { 170 RSAerror(RSA_R_DATA_TOO_LARGE); 171 mlen = -1; 172 } else 173 memcpy(to, db + i, mlen); 174 } 175 } 176 free(db); 177 return mlen; 178 179 decoding_err: 180 /* 181 * To avoid chosen ciphertext attacks, the error message should not 182 * reveal which kind of decoding error happened 183 */ 184 RSAerror(RSA_R_OAEP_DECODING_ERROR); 185 err: 186 free(db); 187 return -1; 188 } 189 190 int 191 PKCS1_MGF1(unsigned char *mask, long len, const unsigned char *seed, 192 long seedlen, const EVP_MD *dgst) 193 { 194 long i, outlen = 0; 195 unsigned char cnt[4]; 196 EVP_MD_CTX c; 197 unsigned char md[EVP_MAX_MD_SIZE]; 198 int mdlen; 199 int rv = -1; 200 201 EVP_MD_CTX_init(&c); 202 mdlen = EVP_MD_size(dgst); 203 if (mdlen < 0) 204 goto err; 205 for (i = 0; outlen < len; i++) { 206 cnt[0] = (unsigned char)((i >> 24) & 255); 207 cnt[1] = (unsigned char)((i >> 16) & 255); 208 cnt[2] = (unsigned char)((i >> 8)) & 255; 209 cnt[3] = (unsigned char)(i & 255); 210 if (!EVP_DigestInit_ex(&c, dgst, NULL) || 211 !EVP_DigestUpdate(&c, seed, seedlen) || 212 !EVP_DigestUpdate(&c, cnt, 4)) 213 goto err; 214 if (outlen + mdlen <= len) { 215 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 216 goto err; 217 outlen += mdlen; 218 } else { 219 if (!EVP_DigestFinal_ex(&c, md, NULL)) 220 goto err; 221 memcpy(mask + outlen, md, len - outlen); 222 outlen = len; 223 } 224 } 225 rv = 0; 226 err: 227 EVP_MD_CTX_cleanup(&c); 228 return rv; 229 } 230 231 static int 232 MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen) 233 { 234 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 235 } 236 #endif 237