Cihat Altuntaş caltuntas

OpenSSL Cheat Sheet 🔐

Install

Install the OpenSSL on Debian based systems

sudo apt-get install openssl

Configure systemd-resolved to use a specific DNS nameserver for a given domain

Use case

Given

I use a VPN to connect to my work network
I'm on a Linux computer that uses systemd-resolved
I have a work domain called example.com
example.com is hosted by both public and private DNS nameservers

Comparison of syntax extensions in Markdown flavors

I created a crude comparison of the syntax of the various common Markdown extensions to have a better view on what are the most common extensions and what is the most widely accepted syntax for them. The list of Markdown flavors that I looked at was based on the list found on CommonMark's GitHub Wiki.

Flavor	Superscript	Subscript	Deletion* Strikethrough	Insertion*	Highlight*	Footnote	Task list	Table	Abbr	Deflist	Smart typo	TOC	Math	Math Block	Mermaid
GFM

Help my SSH keys are unavailable after restart

I'm still not sure what but on both my systems my keys just don't get loaded back into the ssh-agent on restarts and new login sessions. I got annoyed enough at it that I jumped through the hoops of putting ssh-add into a script and writting a property list file to load as a launchagent to fix it.

Add SSH Keys

If you haven't done so already you can use the well written gub hub instructions for generating ssh keys. Once you get them generated you'll add them with ssh-add -K <sshkey> where sshkey is the file path/name. Keys are stored by default in your ~/.ssh folder

Update

Note that you may need to use ssh-add --apple-use-keychain in Big Sur onward instead of ssh-add -K. I discovered the issue in Montery after skipping Big Sur.

Manual reloading SSH keys

The manual method (assuming your keys were stored into the Mac OS Keychain) is to open up Terminal

Reversing Raw Binary Firmware Files in Ghidra

This brief tutorial will show you how to go about analyzing a raw binary firmware image in Ghidra.

Prep work in Binwalk

I was recently interested in reversing some older Cisco IOS images. Those images come in the form of a single binary blob, without any sort of ELF, Mach-o, or PE header to describe the binary.

While I am using Cisco IOS Images in this example, the same process should apply to other Raw Binary Firmware Images.

How to use PlantUML with Markdown

PlantUML is a really awesome way to create diagrams by writing code instead of drawing and dragging visual elements. Markdown is a really nice documentation tool.

Here's how I combine the two, to create docs with embedded diagrams.

Step 0: Setup

Get the command-line PlantUML from the download page or your relevant package manager.

This will guide you through setting up a replica set in a docker environment using.

Docker Compose
MongoDB Replica Sets
Mongoose
Mongoose Transactions

Thanks to https://gist.github.com/asoorm for helping with their docker-compose file!

Using SSH to set up a VPN

https://wiki.archlinux.org/index.php/VPN_over_SSH

If you're a roaming user or you're trying to link a satellite office to the main network, SSH can handle the job. Other solutions exist, and SSH isn't perfect, but this is probably the simplest trick out there.

OpenSSH since version 4.3 has the ability to set up TUN/TAP tunnels. I'm sure most of you have set up port-forwarding via SSH, but this is a little

vimgrep

Vimcasts on vimgrep
Uses native vim regexes (which are slightly different from the regexes used by grep, ack, ag, etc) so the patterns are the same as with vim's within-file search patterns.

You can do a normal within-file search first, then re-use the same pattern to

	# Save as ~/.mailcap. Then use run-mailcap to:
	#
	# - open files by `run-mailcap --action=view <file>`, or
	# - view them in the terminal by `run-mailcap --action=cat <file>`.
	#
	# Useful
	#
	# - in mutt by `set mailcap_file $HOME/.mailcap`
	# - in Vim by adding to your vimrc
	#