Secure IOT (Arduino Server)
---------------------------

There are many ways to secure and authenticate a networking communication, but not all solutions will run on a microcontroller, where processing power and memory is a scarce resource.

How does it work?
~~~~~~~~~~~~~~~~~

+Server -> the iot device that will receive the command+

+Client -> the command sender+


. The Client connects to the Server.

. [ Optional: The Client sends a predefined ammount of data for the Server to wake up. (Some libraries need the client to send first data, else they will not recognize that a connection was just made.) ]

. The Server sends a challenge to be solved.

. The Client send the solved challenge with the command.

. The Server extracts the command from the response/solution, executes it [Optional: sends back the response ].

. [ Optional: The Client extracs the execution response from the Server response. ]



Implementation
~~~~~~~~~~~~~~

Server + Client Requirements
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

- set the same initial data length (0-n)
- set the same hashing function
- set the same symmetric password

Data
^^^^

. [ Optional: Client Sends: 1-n bytes (wake up packet) ]

. Server: Sends Challenge (1-n bytes)

. Client: Sends solved challenge ( Len(hash) bytes)

. [ Optional: Server: Sends Response ( Len(hash) bytes) ]


Methodology
^^^^^^^^^^^

. [ Optional: The Client after connection, sends a predefined number of bytes. ]

. The Server generates and sends a random number (bigger -> more secure) for each connection.
. The Client calculates and sends the HMAC of (random server data + command) using the shared secret password

. The Server tries to find what possible command could the Client have sent 
(calculates HMAC of random server data + possible command, using the shared secret password and compares them)
and then calls the corresponding function. [ Optional: The response of that function is then calculated 
(HMAC of random server data + response, using the shared secret password) and sent to the Client. ]

. [ Optional: The Client tries to find what possible response command could the Server have sent
(calculates HMAC of random server data + response command, using the shared secret password) ]



Considerations
~~~~~~~~~~~~~~

Pros
^^^^

- Minimalistyc nor verbose
- minimal memory usage*
- minimal cpu usage*
- fast**
- authentication
- confidentiality
- replay protection

*with the use of appropriate hashing functions

**when a limited ammount of commands is used

Cons
^^^^

- uses symetric cryptography
- is not designed to send multiple bytes (1 byte commands recommended)
- requires a random seed

Proof of Concept
~~~~~~~~~~~~~~~~

Tested and fully working demo is attached!

This demo was implemented on a pc (Node.JS Client) and an arduino pro mini with an ethernet shield (Server).