code: function(key, seqNum, record) {
    /* MAC is computed like so:
    HMAC_hash(
      key, seqNum +
        TLSCompressed.type +
        TLSCompressed.version +
        TLSCompressed.length +
        TLSCompressed.fragment)
    */
    var hmac = forge.hmac.create();
    hmac.start('SHA1', key);
    var b = forge.util.createBuffer();
    b.putInt32(seqNum[0]);
    b.putInt32(seqNum[1]);
    b.putByte(record.type);
    b.putByte(record.version.major);
    b.putByte(record.version.minor);
    b.putInt16(record.length);
    b.putBytes(record.fragment.bytes());
    hmac.update(b.getBytes());
    return hmac.digest().getBytes();
  }
docs: Gets a MAC for a record using the SHA-1 hash algorithm.
  
  @param key the mac key.
  @param state the sequence number (array of two 32-bit integers).
  @param record the record.
  
  @return the sha-1 hash (20 bytes) for the given record.