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I bricked my Christmas lights

whizzy.org

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Re: I bricked my Christmas lights

#11

Post by willcooke »

MarkusWandel wrote: post #8

Power supply failure? The WS281x things can go really bright, and, in bulk, suck an awful lot of current. A 12V, 3A power supply on a strip of 100 is just about enough to drive them all to full bright white, and dazzlingly bright it is. So I'd look for a blown fuse. The fact that the firmware only drives them to 31 out of a possible maximum brightness of 255 offers a clue.

Good idea! I’ll get the multimeter out.

Re: I bricked my Christmas lights

#14

Post by [deleted] »

EvanAnderson wrote: post #7
Someone wrote: post #4

FTA: > When we try and decrypt the on and off packets we get: > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > Success! This is a lot more sensible. A fixed header, by…

That "54 55 52 4E" jumped right out to my eye as the uppercase alphabet. Knowing that numbers start at 0x30, uppercase letters start at 0x41, and lowercase letters start at 0x61 makes alphanumeric patterns in hex dumps easy to spot. That knowledge is good for short strings, but the canonical hexdump format is a the best way to look at packet and memory dumps.

[deleted]

Re: I bricked my Christmas lights

#16

Post by ww520 »

Someone wrote: post #4

FTA: > When we try and decrypt the on and off packets we get: > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 01 00 00 00 00 00 00 00 00 00 00 > 05 54 55 52 4E 00 00 00 00 00 00 00 00 00 00 00 > Success! This is a lot more sensible. A fixed header, by…

That's a great catch. 0x54 55 52 4E indeed are T U R N.

Re: I bricked my Christmas lights

#19

Post by steviej »

syntaxing wrote: post #17

Beginners question, is there a reason we can’t reverse engineer something similar for lights made by Govee? Is it because it’s WiFi and harder to MITM?

I have a couple of Govee light bulbs in my garage I control with an M5StickC using BLE: https://github.com/stevenjohnstone/reversing-tools/blob/main... . Looking at the decompiled Govee android app, there are many products with similar control over BLE in addition to wifi.

Re: I bricked my Christmas lights

#20

Post by gsharma »

syntaxing wrote: post #17

Beginners question, is there a reason we can’t reverse engineer something similar for lights made by Govee? Is it because it’s WiFi and harder to MITM?

The Govee strips I have do support Bluetooth connectivity. In fact, that’s how they are setup initially.

Your comment prompted me to search for “Govee LAN” and found HomeAssistant LAN integration. Time to dig deeper!

https://www.reddit.com/r/homeassistant/s/bppM4AR3uA

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