PWR switch post
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content/rambles/pwr-switch.md
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content/rambles/pwr-switch.md
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---
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title: "PWR Switch"
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date: "2022-10-14T10:50:56+02:00"
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author: "$HUMANOID"
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tags: ["linux", "ssh", "iot"]
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description: "Hacked together IOT setup with some semblance of security"
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---
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# Introduction
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As we all know, the "S" in IOT stands for security.
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We've all seen countless stories of people's networks getting hijacked due to some 3 year old vulnerability in the software stack of their *insert smart device here*.
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These things barely get any patches at all.
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On top of that, the most they do is spy on you and send [your footage to the police without asking for your consent](https://edition.cnn.com/2022/07/14/tech/amazon-ring-police-footage/index.html "Load without JS to make the page behave.").
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Still, on the other hand, it can be really convenient to be able to control some of the electronics in your home without having to walk towards them.
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I personally have a lamp that I frequently forget to turn off when leaving my room.
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The solution was an [Olimex PWR-switch](https://www.olimex.com/Products/Duino/Shields/PWR-SWITCH/) in combination with a Raspberry Pi 4 that I have running 24/7 regardless (mostly to watch YouTube videos and listen to music over my speaker set; I might write a post about this beautifully hacky contraption at some point in the future).
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# Setup
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Setting it up was relatively easy.
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First I connected my lamp to a European extension cord socket to a random power cable I still had laying around.
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Then I hooked that up to my PWR-switch and plugged my lamp into that contraption.
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From there I got little bag of jumper wires from my local electronics store and hooked up the PWR-switch to my Raspberry Pi.
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I hooked up the PWR-switch's positive to `GPIO 15` and it's ground to the preceding `ground` pin.
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[Here's](https://pinout.xyz) a reference page.
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_Note_, `GPIO 15` is in reference to pin number 10 and the preceding ground pin is pin number 6.
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From there I looked up how to send power to `GPIO 15` in order to have it switch to on.
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The first step to this end is to initialise the pin.
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This can be done with:
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```sh
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echo 15 > /sys/class/gpio/export
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echo out > /sys/class/gpio/gpio15/direction
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```
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Then, sending power to it can be done using something like...
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```sh
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echo 1 > /sys/class/gpio/gpio15/value
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```
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...and the opposite can be done using:
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```sh
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echo 0 > /sys/class/gpio/gpio15/value
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```
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Deinitialising the pin can be done with:
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```sh
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echo 15 > /sys/class/gpio/unexport
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```
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To make this all a little easier I have written a wrapper in POSIX Shell:
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{{< start-details summary="Click to see script" >}}
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```sh
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#!/bin/sh
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INIT_PIN(){
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# the PWR-SWITCH is connected to GPIO 15 and the preceding ground pin
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# reference page https://pinout.xyz/pinout/
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[ -d /sys/class/gpio/gpio15 ] && echo "Pin already initialised" && exit 0
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echo 15 > /sys/class/gpio/export
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echo out > /sys/class/gpio/gpio15/direction
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}
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DEINIT_PIN(){
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[ -d /sys/class/gpio/gpio15 ] || echo "Pin not initialised" && exit 0
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echo 15 > /sys/class/gpio/unexport
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}
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PIN_STATUS(){
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if [ -d /sys/class/gpio/gpio15 ] ; then
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echo "pin status: Pin initialised"
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else
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echo "pin status: Pin not initialised"
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fi
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}
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SWITCH_ON(){
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# initialise pin before doing anything
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[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
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echo 1 > /sys/class/gpio/gpio15/value
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}
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SWITCH_OFF(){
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# initialise pin before doing anything
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[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
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echo 0 > /sys/class/gpio/gpio15/value
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}
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TOGGLE_SWITCH(){
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# initialise pin before doing anything
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[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
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case $(cat /sys/class/gpio/gpio15/value) in
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1) SWITCH_OFF;;
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0) SWITCH_ON;;
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esac
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}
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USAGE(){
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cat >&2 <<EOF
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Usage: pwr-switch <on|off|init|deinit>
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on: send on signal
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off: send off signal
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init: initialise pin
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deinit: deinitialise pin
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status: show pin initialisation state
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toggle: toggle on/off signal
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EOF
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}
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case $1 in
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on) SWITCH_ON;;
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off) SWITCH_OFF;;
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init) INIT_PIN;;
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deinit) DEINIT_PIN;;
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status) PIN_STATUS;;
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toggle) TOGGLE_SWITCH;;
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*) USAGE;;
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esac
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```
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{{< end-details >}}
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You could probably also do this in Python, but my knowledge of Python is nearly none.
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# Remote interaction
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You can probably make a guess as to how I set up the automation and interaction from other devices.
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That's right, I used an SSH forced command:
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```
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no-pty,command="/usr/local/sbin/pwr-switch toggle" ssh-ed25519 <contents of <lamp-key>.pub>
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```
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The unique thing here being that it needs to be executed as the root user in order to mess with the state of the pins.
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(Or at least in the case of my setup.)
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So having it be a forced command is a security benefit here as it prevents whatever device you're using to toggle your lamp from having to log in as the root user.
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All a device with the `<lamp-key>` can do, is toggle the state of `GPIO 15`.
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You could contrivedly call this SIOT...
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Since Android 12, there is the "Device controls" tile in the swipe-down-from-the-top-of-the-screen-menu.
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Termux can interact with the API that this system provides and allows you to add buttons corresponding to Termux' shortcuts.
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These shortcuts are executables found in `~/.shortcuts` within the Termux environment.
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Here I've created a little script that logs into my Raspberry Pi using the `<lamp-key>`, allowing me to toggle my lamp at the tap of a button as long as I'm on my home network.
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Subproject commit 830a4225322572492deef242a15f945b3f02d4e6
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Subproject commit 8122d5eb1ae06319cfc007454cd1ad46658aef1c
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