_ Git - BoarSSL/blob - SSLTLS/RecordDecryptCCM.cs

   1 /*
   2  * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 using System;
  26 using System.Text;
  27
  28 using Crypto;
  29
  30 namespace SSLTLS {
  31
  32 internal class RecordDecryptCCM : RecordDecrypt {
  33
  34         IBlockCipher bc;
  35         byte[] iv;
  36         ulong seq;
  37         byte[] tmp, tag, ctr, cbcmac;
  38         bool ccm8;
  39
  40         internal RecordDecryptCCM(IBlockCipher bc, byte[] iv, bool ccm8)
  41         {
  42                 this.bc = bc;
  43                 this.iv = new byte[12];
  44                 Array.Copy(iv, 0, this.iv, 0, 4);
  45                 seq = 0;
  46                 tag = new byte[16];
  47                 tmp = new byte[32];
  48                 ctr = new byte[16];
  49                 cbcmac = new byte[16];
  50                 this.ccm8 = ccm8;
  51         }
  52
  53         internal override bool CheckLength(int len)
  54         {
  55                 int tagLen = ccm8 ? 8 : 16;
  56                 return len >= (8 + tagLen) && len <= (16384 + 8 + tagLen);
  57         }
  58
  59         internal override bool Decrypt(int recordType, int version,
  60                 byte[] data, ref int off, ref int len)
  61         {
  62                 Array.Copy(data, off, iv, 4, 8);
  63                 off += 8;
  64                 len -= ccm8 ? 16 : 24;
  65
  66                 /*
  67                  * Assemble block B0 and AAD.
  68                  */
  69                 tmp[0] = (byte)(0x40 | ((ccm8 ? 6 : 14) << 2) | 2);
  70                 Array.Copy(iv, 0, tmp, 1, 12);
  71                 tmp[13] = 0;
  72                 IO.Enc16be(len, tmp, 14);
  73
  74                 tmp[16] = 0;
  75                 tmp[17] = 13;
  76                 IO.Enc64be(seq, tmp, 18);
  77                 IO.WriteHeader(recordType, version, len, tmp, 26);
  78                 tmp[31] = 0;
  79                 seq ++;
  80
  81                 for (int i = 0; i < cbcmac.Length; i ++) {
  82                         cbcmac[i] = 0;
  83                 }
  84                 bc.CBCMac(cbcmac, tmp, 0, 32);
  85
  86                 /*
  87                  * Make initial counter value, and compute tag mask.
  88                  * Since the counter least significant byte has value 0,
  89                  * getting it to the next value is simple and requires
  90                  * no carry propagation.
  91                  */
  92                 ctr[0] = 2;
  93                 Array.Copy(iv, 0, ctr, 1, 12);
  94                 for (int i = 13; i < 16; i ++) {
  95                         ctr[i] = 0;
  96                 }
  97                 Array.Copy(ctr, 0, tag, 0, 16);
  98                 bc.BlockEncrypt(tag);
  99                 ctr[15] = 1;
 100
 101                 /*
 102                  * Perform CTR decryption, and compute CBC-MAC. Since
 103                  * CBC-MAC requires full blocks, we have to do the
 104                  * processing of the last partial block in a temporary
 105                  * buffer. The CBC-MAC is computed on the plaintext,
 106                  * padded with zeros in the last block.
 107                  */
 108                 int len1 = len & ~15;
 109                 int len2 = len - len1;
 110                 bc.CTRCBCRun(ctr, cbcmac, true, data, off, len1);
 111                 if (len2 > 0) {
 112                         bc.BlockEncrypt(ctr);
 113                         for (int i = 0; i < len2; i ++) {
 114                                 data[off + len1 + i] ^= ctr[i];
 115                         }
 116                         Array.Copy(data, off + len1, tmp, 0, len2);
 117                         for (int i = len2; i < 16; i ++) {
 118                                 tmp[i] = 0;
 119                         }
 120                         bc.CBCMac(cbcmac, tmp, 0, 16);
 121                 }
 122
 123                 /*
 124                  * Check that the record MAC matches the expected value
 125                  * (taking into account the tag mask).
 126                  */
 127                 int z = 0;
 128                 for (int i = 0; i < (ccm8 ? 8 : 16); i ++) {
 129                         z |= cbcmac[i] ^ tag[i] ^ data[off + len + i];
 130                 }
 131                 return z == 0;
 132         }
 133 }
 134
 135 }