Felix Rusu from lowpowerlab.com has created an amazing library for the Arduino/ATMega platform to use cheap RFM69 wireless modules for wireless transmissions between nodes. For a list of all the features, see his readme: https://github.com/LowPowerLab/RFM69. His Moteino platform and library are perfect for roll-your-own home automation systems, which is just what I am doing!
However, in my mind the library was lacking one critical piece – being able to prevent wireless replay attacks. Using Felix’s library, RFM69 transmissions can be encrypted in hardware, but the receiving node had no way of verifying that the incoming transmission was from a legitimate node and should be processed. If an attacker captured a sensitive packet as it flew through the air, such as one to open your garage door, they could replay it at a time of their choosing and trick your home automation system into opening the door.
TomWS on the lowpowerlab forum and I did some brain storming and he proposed modifications to the base RFM69 library to virtualize some functions, allowing them to be overloaded to create ‘extensions’. Using his modification, I wrote a transmission session key extension.
More after the break…
Continue reading Session Key support for Arduino with RFM69 wireless module
There are numerous python libraries out there for the 16 port MCP23017 GPIO expander chip that works with the Raspberry Pi, so why yet another one? None of the ones I could find actually implement interrupts via the chip Polling is not ideal for my home monitoring setup. I was already monitoring via interrupts and the onboard GPIO pins using the awesome RPIO module and wanted to continue using interrupts with the expansion chip. So I built my own module, leveraging Adafruit’s I2C library for the nitty gritty backend interface.
- Simple digital input and output via all pins
- Input interrupts
- Interrupt port mirroring is configurable – either INTA and INTB can trigger independently for their respective GPIO port banks, or both INTA and INTB can trigger at the same time regardless of what GPIO pin causes the interrupt
- Configurable interrupt polarity – INT could pull the pin high or push it low
- Each GPIO pin can be configured for interrupts independently to either compare against the previous value or against a default pin value
- A utility method cleanupInterrupts that can be called periodically to clear the interrupt if it somehow gets stuck on
You can find the library on my BitBucket.
Stick around after the break for a breakdown of how to use it.
Continue reading MCP23017 GPIO Expander python 3 Library – With Interrupts!