Security on Dhiru's Notebook

Supporting HOPERF CMT2300A on Linux

Tue, 23 Dec 2025 00:00:00 +0000

What This Article Covers

This article presents a practical journey to add Linux support for the HOPERF CMT2300A Sub-GHz RF transceiver - starting from extracting register configuration tables out of vendor firmware, to building and testing a Linux driver on real hardware.

You'll learn:

How TP-Link's driver situation motivated this effort
How firmware was extracted and analyzed
How to build and load the custom driver on Raspberry Pi
How to verify real on-air packet RX

This is aimed at embedded Linux developers, reverse engineers, and RF hackers. It is not a beginner Linux kernel tutorial nor a full CMT2300A datasheet walkthrough - focus is on practical bring-up and reproducibility.

Debugging / reversing Firebase gRPC traffic with mitmproxy

Wed, 16 Apr 2025 00:00:00 +0000

Recently, I was stuck in figuring out how the Firebase gRPC calls worked and how I could generate, modify, and replay them. Trapping and modifying the existing gRPC traffic was not working too well. Finally, I took a step back and spent some time on learning how to build and debug simple Firebase applications. This approach helped me tremendously and I was able to make further progress with my original task in almost no time.

Easily verifying certificate chains

Mon, 14 Apr 2025 00:00:00 +0000

Here is a quick script to verify that the certificate chain is valid and will work.

% cat verify-cert-key.sh
#!/usr/bin/env bash

certFile="${1}"
keyFile="${2}"
caFile="${3}"
certPubKey="$(openssl x509 -noout -pubkey -in "${certFile}")"
keyPubKey="$(openssl pkey -pubout -in "${keyFile}")"

if [[ "${certPubKey}" == "${keyPubKey}" ]]
then
 echo "PASS: key and cert match"
else
 echo "FAIL: key and cert DO NOT match"
fi

openssl verify -CAfile "${3}" "${1}"

Easy Taint Tracking - Finding Heartbleed in 2024

Fri, 01 Nov 2024 00:00:00 +0000

Aim

Finding 'Heartbleed' class of bugs with taint analysis.

Background reading: https://heartbleed.com/

Motivation

While Coverity is now able to detect this bug, we wanted to evaluate the state of open-source security tooling in 2024.

Have we been able to reduce the cost of finding such bugs after all these years?

The Idea

Can we find an execution path from the tainted data in the n2s function to sensitive functions?

Since n2s typically operates on network received bytes, it can serve as a taint source.