_ Git - BoarSSL/blob - SSLTLS/RecordEncryptCCM.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 RecordEncryptCCM : RecordEncrypt {
  33
  34         IBlockCipher bc;
  35         byte[] iv;
  36         ulong seq;
  37         byte[] tmp, tag, ctr, cbcmac;
  38         bool ccm8;
  39
  40         internal RecordEncryptCCM(IBlockCipher bc, byte[] iv, bool ccm8)
  41         {
  42                 this.bc = bc;
  43                 this.iv = new byte[4];
  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 void GetMaxPlaintext(ref int start, ref int end)
  54         {
  55                 /*
  56                  * We need room at the start for the record header (5 bytes)
  57                  * and the explicit nonce (8 bytes). We need room at the end
  58                  * for the MAC (16 bytes).
  59                  */
  60                 start += 13;
  61                 end -= ccm8 ? 8 : 16;
  62                 int len = Math.Min(end - start, 16384);
  63                 end = start + len;
  64         }
  65
  66         internal override void Encrypt(int recordType, int version,
  67                 byte[] data, ref int off, ref int len)
  68         {
  69                 /*
  70                  * CBC-MAC starts with block B0, that encodes the
  71                  * nonce, tag length, and data length.
  72                  * It is then followed by the AAD:
  73                  *  - AAD header (length, over 2 bytes in our case)
  74                  *  - TLS sequence number (8 bytes)
  75                  *  - plain record header
  76                  */
  77                 tmp[0] = (byte)(0x40 | ((ccm8 ? 6 : 14) << 2) | 2);
  78                 Array.Copy(iv, 0, tmp, 1, 4);
  79                 IO.Enc64be(seq, tmp, 5);
  80                 tmp[13] = 0;
  81                 IO.Enc16be(len, tmp, 14);
  82
  83                 tmp[16] = 0;
  84                 tmp[17] = 13;
  85                 IO.Enc64be(seq, tmp, 18);
  86                 IO.WriteHeader(recordType, version, len, tmp, 26);
  87                 tmp[31] = 0;
  88
  89                 for (int i = 0; i < cbcmac.Length; i ++) {
  90                         cbcmac[i] = 0;
  91                 }
  92                 bc.CBCMac(cbcmac, tmp, 0, 32);
  93
  94                 /*
  95                  * Make initial counter value, and compute tag mask.
  96                  * Since the counter least significant byte has value 0,
  97                  * getting it to the next value is simple and requires
  98                  * no carry propagation.
  99                  */
 100                 ctr[0] = 2;
 101                 Array.Copy(tmp, 1, ctr, 1, 12);
 102                 for (int i = 13; i < 16; i ++) {
 103                         ctr[i] = 0;
 104                 }
 105                 Array.Copy(ctr, 0, tag, 0, 16);
 106                 bc.BlockEncrypt(tag);
 107                 ctr[15] = 1;
 108
 109                 /*
 110                  * Perform CTR encryption and CBC-MAC. CCM is defined
 111                  * to use CBC-MAC on the plaintext, not the ciphertext,
 112                  * thus we need to set the 'encrypt' flag to false.
 113                  *
 114                  * When the last block is partial, then we must pad
 115                  * the plaintext with zeros, and compute the CBC-MAC
 116                  * on that plaintext.
 117                  */
 118                 int len1 = len & ~15;
 119                 int len2 = len - len1;
 120                 bc.CTRCBCRun(ctr, cbcmac, false, data, off, len1);
 121                 if (len2 > 0) {
 122                         Array.Copy(data, off + len1, tmp, 0, len2);
 123                         for (int i = len2; i < 16; i ++) {
 124                                 tmp[i] = 0;
 125                         }
 126                         bc.CBCMac(cbcmac, tmp, 0, 16);
 127                         bc.BlockEncrypt(ctr);
 128                         for (int i = 0; i < len2; i ++) {
 129                                 data[off + len1 + i] ^= ctr[i];
 130                         }
 131                 }
 132
 133                 /*
 134                  * XOR the CBC-MAC output with the tag mask.
 135                  */
 136                 for (int i = 0; i < (ccm8 ? 8 : 16); i ++) {
 137                         data[off + len + i] = (byte)(tag[i] ^ cbcmac[i]);
 138                 }
 139
 140                 /*
 141                  * Encode the header, and adjust offset / length.
 142                  */
 143                 off -= 13;
 144                 len += ccm8 ? 16 : 24;
 145                 IO.WriteHeader(recordType, version, len, data, off);
 146                 IO.Enc64be(seq, data, off + 5);
 147                 len += 5;
 148
 149                 seq ++;
 150         }
 151 }
 152
 153 }