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 31int 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 dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH); 56 if (dbmask == NULL) 57 { 58 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 59 return 0; 60 } 61 62 to[0] = 0; 63 seed = to + 1; 64 db = to + SHA_DIGEST_LENGTH + 1; 65 66 EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL); 67 memset(db + SHA_DIGEST_LENGTH, 0, 68 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1); 69 db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01; 70 memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen); 71 if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 72 return 0; 73#ifdef PKCS_TESTVECT 74 memcpy(seed, 75 "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 76 20); 77#endif 78 79 MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH); 80 for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 81 db[i] ^= dbmask[i]; 82 83 MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH); 84 for (i = 0; i < SHA_DIGEST_LENGTH; i++) 85 seed[i] ^= seedmask[i]; 86 87 OPENSSL_free(dbmask); 88 return 1; 89 } 90 91int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 92 const unsigned char *from, int flen, int num, 93 const unsigned char *param, int plen) 94 { 95 int i, dblen, mlen = -1; 96 const unsigned char *maskeddb; 97 int lzero; 98 unsigned char *db = NULL, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; 99 int bad = 0; 100 101 if (--num < 2 * SHA_DIGEST_LENGTH + 1) 102 /* 'num' is the length of the modulus, i.e. does not depend on the 103 * particular ciphertext. */ 104 goto decoding_err; 105 106 lzero = num - flen; 107 if (lzero < 0) 108 { 109 /* lzero == -1 */ 110 111 /* signalling this error immediately after detection might allow 112 * for side-channel attacks (e.g. timing if 'plen' is huge 113 * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA Optimal 114 * Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001), 115 * so we use a 'bad' flag */ 116 bad = 1; 117 lzero = 0; 118 } 119 maskeddb = from - lzero + SHA_DIGEST_LENGTH; 120 121 dblen = num - SHA_DIGEST_LENGTH; 122 db = OPENSSL_malloc(dblen); 123 if (db == NULL) 124 { 125 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 126 return -1; 127 } 128 129 MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen); 130 for (i = lzero; i < SHA_DIGEST_LENGTH; i++) 131 seed[i] ^= from[i - lzero]; 132 133 MGF1(db, dblen, seed, SHA_DIGEST_LENGTH); 134 for (i = 0; i < dblen; i++) 135 db[i] ^= maskeddb[i]; 136 137 EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL); 138 139 if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) 140 goto decoding_err; 141 else 142 { 143 for (i = SHA_DIGEST_LENGTH; i < dblen; i++) 144 if (db[i] != 0x00) 145 break; 146 if (db[i] != 0x01 || i++ >= dblen) 147 goto decoding_err; 148 else 149 { 150 /* everything looks OK */ 151 152 mlen = dblen - i; 153 if (tlen < mlen) 154 { 155 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 156 mlen = -1; 157 } 158 else 159 memcpy(to, db + i, mlen); 160 } 161 } 162 OPENSSL_free(db); 163 return mlen; 164 165decoding_err: 166 /* to avoid chosen ciphertext attacks, the error message should not reveal 167 * which kind of decoding error happened */ 168 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 169 if (db != NULL) OPENSSL_free(db); 170 return -1; 171 } 172 173int MGF1(unsigned char *mask, long len, 174 const unsigned char *seed, long seedlen) 175 { 176 long i, outlen = 0; 177 unsigned char cnt[4]; 178 EVP_MD_CTX c; 179 unsigned char md[SHA_DIGEST_LENGTH]; 180 181 EVP_MD_CTX_init(&c); 182 for (i = 0; outlen < len; i++) 183 { 184 cnt[0] = (unsigned char)((i >> 24) & 255); 185 cnt[1] = (unsigned char)((i >> 16) & 255); 186 cnt[2] = (unsigned char)((i >> 8)) & 255; 187 cnt[3] = (unsigned char)(i & 255); 188 EVP_DigestInit_ex(&c,EVP_sha1(), NULL); 189 EVP_DigestUpdate(&c, seed, seedlen); 190 EVP_DigestUpdate(&c, cnt, 4); 191 if (outlen + SHA_DIGEST_LENGTH <= len) 192 { 193 EVP_DigestFinal_ex(&c, mask + outlen, NULL); 194 outlen += SHA_DIGEST_LENGTH; 195 } 196 else 197 { 198 EVP_DigestFinal_ex(&c, md, NULL); 199 memcpy(mask + outlen, md, len - outlen); 200 outlen = len; 201 } 202 } 203 EVP_MD_CTX_cleanup(&c); 204 return 0; 205 } 206#endif 207