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 31static int MGF1(unsigned char *mask, long len, 32 const unsigned char *seed, long seedlen); 33 34int 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 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, (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; 99 const unsigned char *maskeddb; 100 int lzero; 101 unsigned char *db = NULL, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 102 unsigned char *padded_from; 103 int bad = 0; 104 105 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 106 /* 'num' is the length of the modulus, i.e. does not depend on the 107 * particular ciphertext. */ 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 Optimal 116 * Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001), 117 * so we use a 'bad' flag */ 118 bad = 1; 119 lzero = 0; 120 flen = num; /* don't overflow the memcpy to padded_from */ 121 } 122 123 dblen = num - SHA_DIGEST_LENGTH; 124 db = OPENSSL_malloc(dblen + num); 125 if (db == NULL) 126 { 127 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 128 return -1; 129 } 130 131 /* Always do this zero-padding copy (even when lzero == 0) 132 * to avoid leaking timing info about the value of lzero. */ 133 padded_from = db + dblen; 134 memset(padded_from, 0, lzero); 135 memcpy(padded_from + lzero, from, flen); 136 137 maskeddb = padded_from + SHA_DIGEST_LENGTH; 138 139 if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) 140 return -1; 141 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 142 seed[i] ^= padded_from[i]; 143 144 if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) 145 return -1; 146 for (i = 0; i < dblen; i++) 147 db[i] ^= maskeddb[i]; 148 149 if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) 150 return -1; 151 152 if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 153 goto decoding_err; 154 else 155 { 156 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 157 if (db[i] != 0x00) 158 break; 159 if (i == dblen || db[i] != 0x01) 160 goto decoding_err; 161 else 162 { 163 /* everything looks OK */ 164 165 mlen = dblen - ++i; 166 if (tlen < mlen) 167 { 168 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 169 mlen = -1; 170 } 171 else 172 memcpy(to, db + i, mlen); 173 } 174 } 175 OPENSSL_free(db); 176 return mlen; 177 178decoding_err: 179 /* to avoid chosen ciphertext attacks, the error message should not reveal 180 * which kind of decoding error happened */ 181 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 182 if (db != NULL) OPENSSL_free(db); 183 return -1; 184 } 185 186int PKCS1_MGF1(unsigned char *mask, long len, 187 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 188 { 189 long i, outlen = 0; 190 unsigned char cnt[4]; 191 EVP_MD_CTX c; 192 unsigned char md[EVP_MAX_MD_SIZE]; 193 int mdlen; 194 int rv = -1; 195 196 EVP_MD_CTX_init(&c); 197 mdlen = EVP_MD_size(dgst); 198 if (mdlen < 0) 199 goto err; 200 for (i = 0; outlen < len; i++) 201 { 202 cnt[0] = (unsigned char)((i >> 24) & 255); 203 cnt[1] = (unsigned char)((i >> 16) & 255); 204 cnt[2] = (unsigned char)((i >> 8)) & 255; 205 cnt[3] = (unsigned char)(i & 255); 206 if (!EVP_DigestInit_ex(&c,dgst, NULL) 207 || !EVP_DigestUpdate(&c, seed, seedlen) 208 || !EVP_DigestUpdate(&c, cnt, 4)) 209 goto err; 210 if (outlen + mdlen <= len) 211 { 212 if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 213 goto err; 214 outlen += mdlen; 215 } 216 else 217 { 218 if (!EVP_DigestFinal_ex(&c, md, NULL)) 219 goto err; 220 memcpy(mask + outlen, md, len - outlen); 221 outlen = len; 222 } 223 } 224 rv = 0; 225 err: 226 EVP_MD_CTX_cleanup(&c); 227 return rv; 228 } 229 230static int MGF1(unsigned char *mask, long len, const unsigned char *seed, 231 long seedlen) 232 { 233 return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 234 } 235#endif 236