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

   1 /*
   2  * Copyright (c) 2017 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 RecordDecryptGCM : RecordDecrypt {
  33
  34         IBlockCipher bc;
  35         byte[] iv;
  36         byte[] h;
  37         ulong seq;
  38         byte[] tmp, tag;
  39
  40         internal RecordDecryptGCM(IBlockCipher bc, byte[] iv)
  41         {
  42                 this.bc = bc;
  43                 this.iv = new byte[12];
  44                 Array.Copy(iv, 0, this.iv, 0, 4);
  45                 h = new byte[16];
  46                 bc.BlockEncrypt(h);
  47                 seq = 0;
  48                 tag = new byte[16];
  49                 tmp = new byte[29];
  50         }
  51
  52         internal override bool CheckLength(int len)
  53         {
  54                 return len >= 24 && len <= (16384 + 24);
  55         }
  56
  57         internal override bool Decrypt(int recordType, int version,
  58                 byte[] data, ref int off, ref int len)
  59         {
  60                 off += 8;
  61                 len -= 24;
  62                 IO.Enc64be(seq, tmp, 0);
  63                 IO.WriteHeader(recordType, version, len, tmp, 8);
  64                 IO.Enc64be(13 << 3, tmp, 13);
  65                 IO.Enc64be((ulong)len << 3, tmp, 21);
  66                 for (int i = 0; i < 16; i ++) {
  67                         tag[i] = 0;
  68                 }
  69                 GHASH.Run(tag, h, tmp, 0, 13);
  70                 GHASH.Run(tag, h, data, off, len);
  71                 GHASH.Run(tag, h, tmp, 13, 16);
  72                 seq ++;
  73
  74                 Array.Copy(data, off - 8, iv, 4, 8);
  75                 bc.CTRRun(iv, 2, data, off, len);
  76                 bc.CTRRun(iv, 1, data, off + len, 16);
  77
  78                 int z = 0;
  79                 for (int i = 0; i < 16; i ++) {
  80                         z |= tag[i] ^ data[off + len + i];
  81                 }
  82                 return z == 0;
  83         }
  84 }
  85
  86 }