protocol.txt

Protocol description

Generics : 

-encryption used is XXTEA
-CRC types used :
-- Server side (Java):
// calculate checksum 4b
    static long crc4(byte[] array)
    {
        long res = 0;
        for (int i = 0; i < array.length; i++)
        {
            int c = array[i] & 0xFF;
            res = (res << 1) ^ c;
            res = res & 0xFFFFFFFFL;
        }
        return res;
    }

    // calculate checksum 1b
    static byte crc(byte[] array)
    {
        long res = 0;
        for (int i = 0; i < array.length; i++)
        {
            int c = array[i] & 0xFF;
            res = (res << 1) ^ c;
            res = res & 0xFFFFFFFFL;
        }
        return (byte) (res & 0xFF);
    } 
-- Web site (JS) :
function i4things_crc4(c) {
    var crc = 0;
    for (var i = 0; i < c.length; i++) {
        var b = c[i] & 0xFF;
        crc = (crc << 1) ^ b;
        crc = crc & 0xFFFFFFFF;
    };
    return crc;
}

function i4things_crc(c) {
    var crc = 8606;
    for (var i = 0; i < c.length; i++) {
        var b = c[i] & 0xFF;
        crc = (crc << 1) ^ b;
        crc = crc & 0xFFFFFFFF;
    };
    return crc & 0xFF;
}

-- Node side (C)
uint8_t crc(uint8_t buf_[],
                uint16_t end_index_,
                uint16_t start_index)
    {
      uint32_t res = 8606;  // add magic
      for (uint16_t i = start_index; i < end_index_; i++)
      {
        uint8_t c = buf_[i];
        res = (res << 1) ^ c;
        res = res & 0xFFFFFFFF;
      }
      return (uint8_t)(res & 0xFF);
    }

node -> gateway -> server

-encrypt payload with node/user private key ( known only to the owner of the node )
-generate (CRC) and sequence
-add target(gateway id/if public/open then the id is 10) and origin (node id)
-send to gateway
-when gateway receive it  
-add packet size
-add operation id - (1 byte)
-add seq and magic ( 2 bytes) to the message
-add rssi ( 2 bytes) to the message
-add gateway ID ( uint32 )
!WARNING open gateways have even id - ( id % 2 == 0 ) 
-generate CRC (4 bytes)
-encrypt CRC  + message -  with gateway key ( for open/public key is public )
-add to message
-sent to server and send ack to device
-when message arrives to the server
-split gateway id and payload
-search for gateway ID - if not found discard
-decrypt with gateway key 
-split CRC and payload 
-generate CRC on payload and compare with CRC from decrypted - if not match discard
-if gateway id is odd (id % 2 == 1) check if node_id/device_id owned by the same account as the gateway if not discard the message
-if node id do not exists discard message 
-store in in-memory database

server -> client app/html

-client generate request string from:
-8 bytes long int UTC time challenge
-generate and add 4 bytes CRC in front
-encrypt binary with node network key
-add node id in 64bit number in bytes format ( 8 bytes )
-total - 20 bytes - covert to HEX - 40 bytes
-add to REST request

-server find the node id in database if not exist discard request
-decrypt with node network key
-generate CRC and compare with in the message if not the same discard
-collect all data for the day ( or history)
-encrypt every line of data ( triangulated coordinates, rssi, payload) with node network key
-send to client
-client decrypt with node network key
-decrypt internal payload with private key 

app/html-> server -> node 

-client generate request string from:
-8 bytes long int UTC time challenge
-generate and add 4 bytes CRC in front
-encrypt binary with node network key
-add node id in 64bit number in bytes format ( 8 bytes )
-generate 1 byte crc add at front of data and encrypt data with node private key ( known only to the owner of the node )
-add to REST request
-server search for node id - if not found discard
-server decrypt with node network key and generate and check CRC if not match discard
-finds the gateway from which the last message has been received with max rssi
-prepare ( in full gateway to node format - CRC-SEQ-SRC-DEST-DATA - with 0 for seq and crc) if connection to gateway is active and still not reached the limits pet minute then data is sent else stores the payload to the list of messages for this gateway
-stores a link to the payload in a delayQ - with purpose to clear all messages older then 30min
-on the response part on the heartbeat tick ( heartbeats from gateways need to start sending every 1 minute) max 60 messages are collected and no more then 1KB
-when gateway receive the messages for dispatch it schedules them for sending - with hi-priority ACK and low priority notifications, and cycle over notifications until ack is received for every notification or next heartbeat time is due , when heartbeat is received the buffer is overwritten - all non send messages discarded
-when the node receive the message - sends ack back to gateway
-crc is checked and message is decrypted with private key and the CRC