Notes on Dhiru's Notebook

Debugging gaming pads on Linux

Mon, 29 Sep 2025 00:00:00 +0000

While running https://github.com/fhoedemakers/pico-infonesPlus, I found that my SNES gaming pad was not fully supported.

Specifically, the UP/DOWN and LEFT/RIGHT keys were not working.

Let's debug this a bit:

Plug in the gaming pad on a Linux box and run the following command (hidraw5 will need to be changed as needed):

$ lsusb
...
Bus 001 Device 063: ID 0810:e501 Personal Communication Systems, Inc. SNES Gamepad

$ sudo hexdump -C /dev/hidraw5
...
00004a50 01 80 80 7f 7f 0f 00 00 01 80 80 7f 00 0f 00 00 |................|
00004a60 01 80 80 7f 00 0f 00 00 01 80 80 7f 00 0f 00 00 |................|
*
00004a80 01 80 80 7f 7f 0f 00 00 01 80 80 7f 7f 0f 00 00 |................|

This is what I see when pressing the UP key.

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}"