lib/libcrypto/rsa/rsa_oaep.c

   1 /* $OpenBSD: rsa_oaep.c,v 1.26 2017/01/29 17:49:23 beck 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                 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                 RSAerror(ERR_R_MALLOC_FAILURE);
 128                 return -1;
 129         }
 130
 131         /*
 132          * Always do this zero-padding copy (even when lzero == 0)
 133          * to avoid leaking timing info about the value of lzero.
 134          */
 135         padded_from = db + dblen;
 136         memset(padded_from, 0, lzero);
 137         memcpy(padded_from + lzero, from, flen);
 138
 139         maskeddb = padded_from + SHA_DIGEST_LENGTH;
 140
 141         if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
 142                 return -1;
 143         for (i = 0; i < SHA_DIGEST_LENGTH; i++)
 144                 seed[i] ^= padded_from[i];
 145
 146         if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
 147                 return -1;
 148         for (i = 0; i < dblen; i++)
 149                 db[i] ^= maskeddb[i];
 150
 151         if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
 152                 return -1;
 153
 154         if (timingsafe_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
 155                 goto decoding_err;
 156         else {
 157                 for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
 158                         if (db[i] != 0x00)
 159                                 break;
 160                 if (i == dblen || db[i] != 0x01)
 161                         goto decoding_err;
 162                 else {
 163                         /* everything looks OK */
 164
 165                         mlen = dblen - ++i;
 166                         if (tlen < mlen) {
 167                                 RSAerror(RSA_R_DATA_TOO_LARGE);
 168                                 mlen = -1;
 169                         } else
 170                                 memcpy(to, db + i, mlen);
 171                 }
 172         }
 173         free(db);
 174         return mlen;
 175
 176 decoding_err:
 177         /*
 178          * To avoid chosen ciphertext attacks, the error message should not
 179          * reveal which kind of decoding error happened
 180          */
 181         RSAerror(RSA_R_OAEP_DECODING_ERROR);
 182         free(db);
 183         return -1;
 184 }
 185
 186 int
 187 PKCS1_MGF1(unsigned char *mask, long len, const unsigned char *seed,
 188     long seedlen, const EVP_MD *dgst)
 189 {
 190         long i, outlen = 0;
 191         unsigned char cnt[4];
 192         EVP_MD_CTX c;
 193         unsigned char md[EVP_MAX_MD_SIZE];
 194         int mdlen;
 195         int rv = -1;
 196
 197         EVP_MD_CTX_init(&c);
 198         mdlen = EVP_MD_size(dgst);
 199         if (mdlen < 0)
 200                 goto err;
 201         for (i = 0; outlen < len; i++) {
 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                         if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
 212                                 goto err;
 213                         outlen += mdlen;
 214                 } else {
 215                         if (!EVP_DigestFinal_ex(&c, md, NULL))
 216                                 goto err;
 217                         memcpy(mask + outlen, md, len - outlen);
 218                         outlen = len;
 219                 }
 220         }
 221         rv = 0;
 222 err:
 223         EVP_MD_CTX_cleanup(&c);
 224         return rv;
 225 }
 226
 227 static int
 228 MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen)
 229 {
 230         return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
 231 }
 232 #endif