PWR switch post

content/rambles/pwr-switch.md

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+---
+title: "PWR Switch"
+date: "2022-10-14T10:50:56+02:00"
+author: "$HUMANOID"
+tags: ["linux", "ssh", "iot"]
+description: "Hacked together IOT setup with some semblance of security"
+---
+
+# Introduction
+
+As we all know, the "S" in IOT stands for security.
+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*.
+These things barely get any patches at all.
+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.").
+
+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.
+I personally have a lamp that I frequently forget to turn off when leaving my room.
+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).
+
+# Setup
+
+Setting it up was relatively easy.
+
+First I connected my lamp to a European extension cord socket to a random power cable I still had laying around.
+Then I hooked that up to my PWR-switch and plugged my lamp into that contraption.
+
+From there I got little bag of jumper wires from my local electronics store and hooked up the PWR-switch to my Raspberry Pi.
+I hooked up the PWR-switch's positive to `GPIO 15` and it's ground to the preceding `ground` pin.
+[Here's](https://pinout.xyz) a reference page.
+
+_Note_, `GPIO 15` is in reference to pin number 10 and the preceding ground pin is pin number 6.
+
+From there I looked up how to send power to `GPIO 15` in order to have it switch to on.
+The first step to this end is to initialise the pin.
+This can be done with:
+```sh
+echo 15 > /sys/class/gpio/export
+echo out > /sys/class/gpio/gpio15/direction
+```
+Then, sending power to it can be done using something like...
+```sh
+echo 1 > /sys/class/gpio/gpio15/value
+```
+...and the opposite can be done using:
+```sh
+echo 0 > /sys/class/gpio/gpio15/value
+```
+
+Deinitialising the pin can be done with:
+```sh
+echo 15 > /sys/class/gpio/unexport
+```
+To make this all a little easier I have written a wrapper in POSIX Shell:
+{{< start-details summary="Click to see script" >}}
+```sh
+#!/bin/sh
+
+INIT_PIN(){
+	# the PWR-SWITCH is connected to GPIO 15 and the preceding ground pin
+	# reference page https://pinout.xyz/pinout/
+	[ -d /sys/class/gpio/gpio15 ] && echo "Pin already initialised" && exit 0
+	echo 15 > /sys/class/gpio/export
+	echo out > /sys/class/gpio/gpio15/direction
+}
+
+DEINIT_PIN(){
+	[ -d /sys/class/gpio/gpio15 ] || echo "Pin not initialised" && exit 0
+	echo 15 > /sys/class/gpio/unexport
+}
+
+PIN_STATUS(){
+	if [ -d /sys/class/gpio/gpio15 ] ; then
+		echo "pin status: Pin initialised"
+	else
+		echo "pin status: Pin not initialised"
+	fi
+}
+
+SWITCH_ON(){
+	# initialise pin before doing anything
+	[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
+	echo 1 > /sys/class/gpio/gpio15/value
+}
+
+SWITCH_OFF(){
+	# initialise pin before doing anything
+	[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
+	echo 0 > /sys/class/gpio/gpio15/value
+}
+
+TOGGLE_SWITCH(){
+	# initialise pin before doing anything
+	[ -d /sys/class/gpio/gpio15 ] || INIT_PIN
+	case $(cat /sys/class/gpio/gpio15/value) in
+		1) SWITCH_OFF;;
+		0) SWITCH_ON;;
+	esac
+}
+
+USAGE(){
+	cat >&2 <<EOF
+Usage: pwr-switch <on|off|init|deinit>
+	on: send on signal
+	off: send off signal
+	init: initialise pin
+	deinit: deinitialise pin
+	status: show pin initialisation state
+	toggle: toggle on/off signal
+EOF
+}
+
+case $1 in
+	on) SWITCH_ON;;
+	off) SWITCH_OFF;;
+	init) INIT_PIN;;
+	deinit) DEINIT_PIN;;
+	status) PIN_STATUS;;
+	toggle) TOGGLE_SWITCH;;
+	*) USAGE;;
+esac
+```
+{{< end-details >}}
+
+You could probably also do this in Python, but my knowledge of Python is nearly none.
+
+# Remote interaction
+
+You can probably make a guess as to how I set up the automation and interaction from other devices.
+That's right, I used an SSH forced command:
+```
+no-pty,command="/usr/local/sbin/pwr-switch toggle" ssh-ed25519 <contents of <lamp-key>.pub>
+```
+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.
+(Or at least in the case of my setup.)
+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.
+All a device with the `<lamp-key>` can do, is toggle the state of `GPIO 15`.
+
+You could contrivedly call this SIOT...
+
+Since Android 12, there is the "Device controls" tile in the swipe-down-from-the-top-of-the-screen-menu.
+Termux can interact with the API that this system provides and allows you to add buttons corresponding to Termux' shortcuts.
+These shortcuts are executables found in `~/.shortcuts` within the Termux environment.
+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.

themes/vugo

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