Protocol README

daemon/CovertProtocol.md

@@ -2,7 +2,7 @@
 The Covert Protocol is the protocol used to communicate over the covert channel. The communication over the covert channels aims mainly on file transfers.
 
 # Bidirectional Covert Protocol
-A bidirectional communication which uses commands to manage a file transfer.
+A bidirectional communication which uses segment numbers to prevent data loss.
 
 A packet is at least 2 bytes big. The first byte is the header followed by one or multiple data bytes.
 
@@ -17,58 +17,13 @@ A packet is at least 2 bytes big. The first byte is the header followed by one o
 A header contains a command and a segment number. Even if the `no operation` command is used the segment number must be counted.
 
 ```
-|           8 bit           |
-|           header          |
+|          8 bit          |
+|          header         |
 
-| 2 bit |  3 bit  |  3 bit  |
-|  seg  |    -    |   com   |
+| 2 bit |  5 bit  | 1 bit |
+|  seg  |    -    | reset |
 ```
 
-### Command
-Commands which indicate
-
-```
-0x0 no operation
-0x1 send file name size
-0x2 send file name
-0x3 send data size
-0x4 send data
-0x5 -
-0x6 cancel / reset
-0x7 error
-```
-
-The sending commands must be sent in the right order: lower number to higher number
-You can of course send a `no operation` or a `cancel / reset` command. If the order is not followed an `error` answer should be invoked.
-
-
-#### `0x0 no operation`
-No operation is the command which indicates to do nothing. It simply works as ACK to signal the packet was received.
-
-#### `0x1 send file name size`
-A file name size is a one byte number.
-```
-0 < file name size < 256
-```
-
-#### `0x2 send file name`
-A file name is a string which can be up to 255 bytes long.
-This command must be looped until the file name is fully transmitted!
-
-#### `0x3 send data size`
-A data size is a 4 byte unsigned int.
-This command must be looped until the data size is fully transmitted!
-
-#### `0x4 send data`
-Data are as much bytes as communicated in `send data size`.
-This command must be looped until the data is fully transmitted!
-
-#### `0x6 cancel / reset`
-This command resets the transmission. The following segment number is the segment number of the reset packet plus 1.
-
-#### `0x7 error`
-This command signals there was an error and the transmission is to be resetted. The following segment number is the segnemtn number of the error packet plus 1.
-
 
 ### Segment
 The segment number is a counter for the packets in the covert channels. The segment number is increased on the passive server side.
@@ -94,14 +49,16 @@ seg                   seg
   <-------------------- 5
 ```
 
+### Reset
+A reset will will be triggered by a set reset bit.
+Running file transfers will be canceled and the segment counter will be reset to its initial value.
 
+## Data
+The data will be transmitted over a sequential protocol. You could in fact use the data protocol and ditch the bidirectional protocol.
+There are several states of a transfer:
 
-It might happen that a server is not possible to answer or all the answers won't be transmitted. This case should be handled with the `cancel / reset` or `error` command upon reconnection. Maybe the session is recoverable without a reset.
-```
-A                       B
-seg                   seg
-=========================
-1 -------------------->
-1 -------------------->
-1 -------------------->
-```
+0. idle - does nothing
+1. file name size - sends size of file name as 1 byte unsigned int
+2. file name - sends file name chars and loops until the full file name is transmitted
+3. data size - sends 4 bytes of data size and loops until the full data size is transmitted
+4. data - sends n bytes of data and loops until the full file is transmitted