Commands

A command is an instruction from mobile to the dongle, sent in an encrypted packet. This document outlines commands supported by ClickStick platform.

Command structure

Field	Size	Description
Command ID	1 byte	Command identifier
Params	0 – MAX_PARAM_SIZE bytes	Command-specific parameters

• Maximum size of a command structure (MAX_COMMAND_SIZE) is 226 bytes, due to BLE stack constraints. MAX_PARAM_SIZE is thus 225.
• Unrecognized command IDs are discarded without processing.

Supported commands

START_SESSION

Completes session initialization by providing mobile's public ECDH key to the dongle.

• Command ID: 0x00
• Parameters:
  • mobilePublicKey: 32 bytes
• Effect: the dongle computes the sessionKey, resets SEQ counter and switches to IDLE mode. This command is accepted only in INIT_SESSION state and ignored otherwise.

Warning: Basically plaintext

Given that START_SESSION command is part of the session initiation workflow, the peers do not have the sessionKey yet and/or have mismatched seq counters. Therefore, the encrypted packet with this command is encrypted using seq = 0 and all-zero encryption key.

CANCEL

Interrupts command processing and returns the dongle to IDLE state.

• Command ID: 0x01
• Parameters: none
• Effect: the dongle stops processing the current command, clears the command queue, and returns to the IDLE state as soon as possible. This command is ignored in INIT_SESSION state.

PAUSE

Pauses command processing for the given duration

• Command ID: 0x02
• Parameters:
  • Delay: UInt16 (in milliseconds)
  • Dummy: 0 to MAX_PARAM_SIZE - 2 bytes, optional dummy payload for traffic activity obfuscation
• Effect: sets BUSY status and delays processing queued commands for the given duration. The delay can be interrupted by the CANCEL command. This command is ignored in INIT_SESSION state.

TYPE

Emulates pressing and releasing specific keys with a fixed delay

• Command ID: 0x10
• Parameters:
  • Scancodes: 1 to MAX_PARAM_SIZE bytes
• Effect: for each scancode, the dongle produces three actions: a "key press" HID frame, a "key release" frame, and a fixed delay defined by dongle's rate limit (see SR-RateLimit)