Unblocking The Main Thread Solving ANRs and Frozen Frames
1024-bit Encrypted Cloud-Based Garage Door Control
1. 1024-bit Encrypted, Cloud-Based
Garage
Daniel Ng 2012
@embeddedmelb
*Desired Encryption level proportional to paranoia
**Cloud-base-edness optional extra
2. What?
• Open your garage door from your phone
• Over Wi-Fi
• Secure-enough
• Could be over the Internet if you really want
3. Why?
• Garage only had 1 working remote control
• Original replacement cost $200+
• Dodgy after-market replacements
• Phone == Universal Controller
• Just for fun, curiosity, learning.
4. The Gear
• Original push-button
local wired controller
• Any phone with an SSH
Client
• Dreamplug (overkill)
• mbed (also overkill)
• Simple transistor switch
circuit
5. Dreamplug
• Fanless Plug Computer
• <5W consumption
• Built-in Wi-Fi Access
Point
• Runs Linux
• Many other bells &
whistles
6. Phone
• Phone connects to Dreamplug’s built-in Wi-Fi
Access Point
• Phone logs in to Dreamplug with specific
username eg. ‘g’
• Use any phone with a SSH Client
• Eg. ‘ConnectBot’ on an Android Phone
• Optional:
– ConnectBot also has Public-Key Encryption feature
• Convenience of not having to type a password
7. Hacking The Dreamplug
• Hack /etc/passwd for user ‘g’:
g:x:1000:1000:g,,,:/home/g:/sbin/garage
• Create /sbin/garage:
#!/bin/sh
echo "ggg"
echo '1' > /dev/ttyACM0
• Optional:
– Create (eg. 1024-bit) public-key pair for
convenience of not having to type password:
ssh-keygen
8. mbed
• 32-bit ARM Core
• USB
• Lots of GPIOs
• Many other bells &
whistles
10. Now What?
• GPIO pin on mbed goes high for 1 sec.
• We want this to cause the button on the old
controller to be pressed
– ie. close the circuit across the button terminals
• How?
11. Transistor
Circuit
• Transistor acts as a
simple switch
12. Transistors Simplified
• Current entering the Base flows
when the mbed’s GPIO goes HIGH
• The Collector is wired to one of the
button terminals
• The Emitter is wired to the other
button terminal
• Current entering the Base causes
current to flow between the
Collector and Emitter ie. closing the
circuit between the button terminals
13. Summary
• Phone connects to Dreamplug’s Wi-Fi Access
Point
• Phone logs in
• Dreamplug executes hacked login script which
sends a ‘1’ to the USB port
• mbed sees the ‘1’ and turns on the transistor
switch
• Transistor switch ‘presses’ the garage door
button
