Coder Legion - Recent posts tagged using

How does SSH work and how can it be set up?

Wed, 29 Apr 2026 05:42:27 +0000

Hello, I'm Ganesh. I'm building git-lrc, an AI code reviewer that runs on every commit. It is free, unlimited, and source-available on Github. Star Us to help devs discover the project. Do give it a try and share your feedback for improving the product.

Secure Shell (SSH) is a cryptographic network protocol that allows you to operate network services securely over an unsecured network.

It is most commonly used for logging into a remote terminal and executing commands.

How SSH Works

SSH uses a client-server model and relies on a suite of encryption technologies to ensure that data remains confidential and untampered.

1. The Handshake

When we connect to a server, the two machines exchange supported encryption protocols and settle on a mutually compatible version.

They also establish a session key using a process like the Diffie-Hellman algorithm, which allows them to create a shared secret without actually sending the key across the network.

Here is the video explaining this process:
Link

2. Authentication

Once the encrypted channel is established, the server needs to verify who you are. This usually happens in one of two ways:

Password Authentication: You send your password through the encrypted tunnel.
Key-based Authentication: The most secure method, using a Public Key (stored on the server) and a Private Key (stored on your machine).

3. Encryption Layers

SSH utilizes three different types of encryption:

Symmetrical Encryption: Uses one key for both encryption and decryption of the entire session.
Asymmetrical Encryption: Uses a public/private key pair (used primarily during the handshake and for authentication).
Hashing: Uses algorithms (like HMAC) to ensure data integrity, proving that the packets haven't been altered during transit.

For let's setup simple RSA key pair for ubuntu server.

How to Setup SSH

Since we are using ubuntu server, we need to install the SSH server on the server.

Step 1: Install the SSH Server

Assuming you are in cloud console want to setup ssh on ubuntu.

On the server, run:

sudo apt update
sudo apt install openssh-server

To check if it’s running:

sudo systemctl status ssh

Step 2: Generate SSH Keys (Recommended)

On your local machine, generate a key pair. This is much safer than using a password.

ssh-keygen -m PEM -t rsa -b 4096 -f ~/.ssh/private_key

Press Enter to save it in the default location.

You can add a passphrase for extra security.

gk@jarvis:~$ ssh-keygen -m PEM -t rsa -b 4096 -f ~/.ssh/private_key
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/gk/.ssh/private_key
Your public key has been saved in /home/gk/.ssh/private_key.pub
The key fingerprint is:
SHA256:i3qqpQpyRkjDAdnbe++rN+ZCzak/4Ryzsn5vGJYEsVg gk@jarvis
The key's randomart image is:
+---[RSA 4096]----+
|o+    E.         |
|o o  o..         |
| + o. ..         |
|..o .   .        |
|. .  . +So       |
| .  . o.@.       |
|o o .o.*.B       |
|oo o .= % .      |
|..o.o++%=*.      |
+----[SHA256]-----+

In the above output, we have generated a private key and public key.

we can copy public key and save it in server

Step 3: Copy the Key to the Server

Copy public key from local machine.

cat ~/.ssh/private_key.pub

Once you are inside server either in temperary console or using password.

Change directory to .ssh

Add public key to authorized_keys file.

This way server will trust your public key and you can login without a password.

Step 4: Connect

Now you can log in without a password:

ssh username@remote_host_ip

Conclusion

We understood how ssh works and how to setup ssh on server.

I hope this article helps you to understand ssh and how to setup ssh on server.

Any feedback or contributors are welcome! It’s online, source-available, and ready for anyone to use.
⭐ Star it on GitHub: https://github.com/HexmosTech/git-lrc

How to Connect a DHT11 to a NodeMCU v2 board?

Tue, 14 Apr 2026 20:49:32 +0000

In this article, we will see how to work with DHT11 sensor with NodeMCU v2 using PlatformIO.

Hardware Check

We should always check datasheets before working with any hardware.

So, by checking the datasheet of DHT11 and NodeMCU v2, we can determine how connection should be done and how to create firmware for it.

You can check datasheets here:

Power Compatibility

As per the datasheet of DHT11, it can operate on a supply range of 3V to 5.5V DC.
Since the NodeMCU v2 runs on 3.3V.

You can power the sensor directly from the NodeMCU's 3V3 pin. This keeps your build simple and safe without needing extra voltage regulators.

Also they recommend to use a pull-up resistor of 4.7K to 10K between VDD and DATA pins.To make sure data is read properly.

Hardware Identification

Check which version of the DHT11 you have. This changes how many pins you’ll be dealing with.

Feature	Bare DHT11 Sensor	DHT11 Module
Appearance	Blue plastic square with 4 metal pins.	Sensor soldered onto a small PCB.
Pin Count	4 Pins.	3 Pins.
Resistor	Required. You must add your own 4.7K to 10K resistor.	Built-in. Usually pre-soldered on the board.

Step-by-Step Wiring Guide

For the 4-Pin Bare Sensor

If you are using the bare sensor, follow this pinout based on the official datasheet:

Pin 1 (VDD): Connect to the 3V3 pin on the NodeMCU.
Pin 2 (DATA): Connect to a digital pin like D1 or D2.
- Crucial Step: Place a 4.7K to 10K pull-up resistor between Pin 1 (VDD) and Pin 2 (DATA). This prevents the signal from "floating" and ensures stable data readings.
Pin 3 (NULL): Leave this disconnected. It serves no electrical purpose.
Pin 4 (GND): Connect to any GND pin on the NodeMCU.

For the 3-Pin Module

If you have the module, life is even easier. The board is usually labeled:

VCC (+): Connect to 3V3.
DATA (out): Connect to D1 or D2.
GND (-): Connect to GND.

Why the Pull-up Resistor Matters?

Without a pull-up resistor, the DATA line doesn't have a clear "High" or "Low" state when the sensor isn't talking, which leads to erratic readings or "Sensor not found" errors.

If you're using the bare sensor, don't skip the 4.7K to 10K resistor (though anything from 4.7K to 10K usually works in a pinch!).

Coding Your DHT11 with PlatformIO

Now that the hardware is ready.

Since we are using PlatformIO, we’ll need to configure our project environment and use the industry-standard Adafruit library.

1. Configure `platformio.ini`

First, we need to tell PlatformIO which board we are using and which library to download. Open your platformio.ini file and ensure it looks like this:

[env:nodemcuv2]
platform = espressif8266
board = nodemcuv2
framework = arduino
monitor_speed = 115200
lib_deps = 
    adafruit/DHT sensor library @ ^1.4.6
    adafruit/Adafruit Unified Sensor @ ^1.1.14

Note: The Adafruit Unified Sensor library is a hidden dependency that the DHT library needs to function correctly.

2. The Main Code (`src/main.cpp`)

In your project’s src folder, open main.cpp. We’ll use a modified version of your snippet specifically tuned for the DHT11.

#include <Arduino.h>
#include "DHT.h"

// Define the NodeMCU pin connected to the DHT11 data pin
// Using D2 (GPIO 4) as per our wiring guide
#define DHTPIN D2     

// Since we are using the DHT11, we specify it here
#define DHTTYPE DHT11   

// Initialize the DHT sensor
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  // Start serial communication at the speed defined in platformio.ini
  Serial.begin(115200);
  Serial.println(F("DHT11 Sensor Initializing..."));

  // Start the sensor
  dht.begin();
}

void loop() {
  // Wait 2 seconds between measurements. 
  // DHT11 is slower than modern sensors; don't rush it!
  delay(2000);

  // Reading temperature or humidity takes about 250 milliseconds!
  float h = dht.readHumidity();
  float t = dht.readTemperature(); // Celsius
  float f = dht.readTemperature(true); // Fahrenheit

  // Check if any reads failed
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Failed to read from DHT sensor! Check your wiring."));
    return;
  }

  // Compute heat index (how it actually feels)
  float hic = dht.computeHeatIndex(t, h, false);

  // Print results to the Serial Monitor
  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  |  Temp: "));
  Serial.print(t);
  Serial.print(F("°C  |  Heat Index: "));
  Serial.print(hic);
  Serial.println(F("°C"));
}

DHT11 Sensor Initializing...
Humidity: 45.00 %  |  Temp: 25.00°C  |  Heat Index: 25.00°C
Humidity: 46.00 %  |  Temp: 25.12°C  |  Heat Index: 25.12°C
Humidity: 45.00 %  |  Temp: 25.25°C  |  Heat Index: 25.25°C

Key Adjustments for the DHT11

DHTTYPE: Ensure this is set to DHT11. While the code for a DHT22 is almost identical, the timing and data conversion logic inside the library are different for these two models.
Sampling Rate: The DHT11 has a sampling rate of about 1Hz (one reading per second). Using a delay(2000) (2 seconds) is a "safe bet" to ensure you don't get stale data or errors.
Accuracy Note: Don't be surprised if the readings are slightly different from your home thermostat. The DHT11 is an entry-level sensor with an accuracy of ±2°C for temperature and ±5% for humidity.

Conclusion

We could able to connect DHT11 sensor with NodeMCU v2 using PlatformIO and read temperature and humidity values.

In next article we will learn different sensor.

Any feedback or contributors are welcome! It’s online, source-available, and ready for anyone to use.
⭐ Star it on GitHub: https://github.com/HexmosTech/git-lrc

Introduction to Go generics?

Mon, 30 Mar 2026 21:36:35 +0000

Hello, I'm Ganesh Kumar. I'm working on git-lrc: a Git hook for Checking AI generated code.AI agents write code fast. They also silently remove logic, change behavior, and introduce bugs -- without telling you. You often find out in production.git-lrc fixes this. It hooks into git commit and reviews every diff before it lands. 60-second setup. Completely free.

In my previous post, I explained how to work with an interface.

Now let's understand go generics.

Why is Go Generics needed?

Before I start explaining go generics, let me give an example of a simple code without using go generics.

Let's have a simple function for finding the index of the element.
We can see that both internal workings are the same, but the parameters and return variable types are different




package main

import "fmt"



func IndexInt (s []int,x int) int{

    for i, v := range s{
        if v == x{
            return i
 }

 } 
        return -1

}

func IndexString (s []string,x string) int{

    for i, v := range s{
        if v == x{
            return i
 }

 } 
        return -1

}


func main(){

    integer := []int{10,20,30,35,40,45}
    fmt.Println(IndexInt(integer, 35)) 

    strings := []string{"hello", "world"}
    fmt.Println(IndexString(strings, "example")) 
}

As we can see, both are working in the same way.
Output:

gk@jarvis:~/exp/code/rd/go-exmaple$ go run main.go 
3
-1

So, why can't we have a single function that does the same task with passing different types? This is how go generics play a major role in this.

What is Go Generics?

It is a feature that allows developers to write reusable, type-safe code that works with multiple types.

That means we can use Go generics to solve our problem.

In the example below, we will solve the above problem.

Using Go Generics

There are many constraints to using go generics.

For our case let's just use a comparable constraint.

let't create function Index with [T comparable] with using T as type.


package main

import "fmt"



func Index[T comparable] (s []T,x T) int{

    for i, v := range s{
        if v == x{
            return i
 }

 } 
        return -1

}


func main(){

    integer := []int{10,20,30,35,40,45}
    fmt.Println(Index(integer, 35)) 

    strings := []string{"hello", "world"}
    fmt.Println(Index(strings, "example")) 
}

As we expected, we got the same results with one function.

Output

gk@jarvis:~/exp/code/rd/go-exmaple$ go run main.go 
3
-1

Conclusion

Go Generics was introduced recently we might be using it in a few cases where it is necessary.

Check out: git-lrc
Any feedback or contributors are welcome! It’s online, open-source, and ready for anyone to use.
⭐ Star it on GitHub:

HexmosTech / git-lrc

Free, Unlimited AI Code Reviews That Run on Commit

git-lrc

Free, Unlimited AI Code Reviews That Run on Commit

AI agents write code fast. They also silently remove logic, change behavior, and introduce bugs -- without telling you. You often find out in production.

git-lrc fixes this. It hooks into git commit and reviews every diff before it lands. 60-second setup. Completely free.

See It In Action

See git-lrc catch serious security issues such as leaked credentials, expensive cloud operations, and sensitive material in log statements

git-lrc-intro-60s.mp4

Why

AI agents silently break things. Code removed. Logic changed. Edge cases gone. You won't notice until production.
Catch it before it ships. AI-powered inline comments show you exactly what changed and what looks wrong.
Build a habit, ship better code. Regular review → fewer bugs → more robust code → better results in your team.
Why git? Git is universal. Every editor, every IDE, every AI…

View on GitHub

Using the Internet Securely

Tue, 18 Mar 2025 21:50:36 +0000

The internet is a powerful tool, but it comes with risks. Securing your online presence is essential to protect your data, privacy, and communications. One of the most effective tools for encryption and authentication is GNU Privacy Guard (GnuPG), which implements the Pretty Good Privacy (PGP) - Wikipedia standard. This guide covers the basics of GPG/PGP keys and general security practices for safer internet usage.

Understanding GPG/PGP Keys

PGP and GPG use public-key cryptography to encrypt and sign data. Each user has a key pair:

Public Key: Shared with others to encrypt messages for you.
Private Key: Kept secret and used to decrypt messages and sign data.

By using GPG, you can send encrypted emails, verify software integrity, and authenticate communications.

Generating a GPG Key

To create a new GPG key:

Install GPG:
- Linux/macOS: Check installation with gpg --version. If not installed, install it using:
  - macOS: brew install gnupg
  - Linux (Debian-based): sudo apt install gnupg
- Windows: Use Gpg4win
Generate a key:
```
gpg --full-generate-key
```
Follow the prompts to select key type, size, and expiration.

Export your public key:

gpg --export --armor your@email.com > publickey.asc

Share the public key so others can encrypt messages for you. You can upload it to a keyserver like:
- keyserver.ubuntu.com
- keys.openpgp.org

Encrypting and Signing Messages

To encrypt a message:

echo "Confidential message" | gpg --encrypt --armor -r recipient@email.com

To sign a message:

echo "Important document" | gpg --clearsign

To verify a signed message:

gpg --verify message.asc

For more details, refer to the GPG Command Line Guide.

General Internet Security Practices

Use Strong, Unique Passwords

Avoid reusing passwords across different sites.
Use a password manager to store and generate strong passwords.
Recommended Password Manager: GNU Pass (A simple command-line password manager using GPG encryption).
Alternative: KeePassXC (A libre, cross-platform password manager).

Secure Your Email and Communications

Use end-to-end encrypted email services like ProtonMail.
Consider self-hosted email solutions for full privacy, such as SnappyMail (a lightweight, privacy-focused webmail client).
Prefer encrypted messaging apps like Element (Matrix-based).

Keep Software Updated

Regularly update your operating system, browser, and software.
Avoid using outdated plugins and extensions that may introduce vulnerabilities.
Enable automatic updates wherever possible.

Browse the Web Safely

Always use HTTPS.
Avoid clicking on suspicious links or downloading unknown attachments.
Use a privacy-focused browser like:
- LibreWolf (A hardened fork of Firefox with enhanced privacy settings).
- Tor Browser (For anonymous browsing via the Tor network).
- Firefox (Configure it for privacy).
Consider using a libre VPN like Mullvad or Riseup VPN to hide your IP address and encrypt traffic.

Verify Software Integrity

When downloading software, always check its authenticity by verifying its GPG signature:

gpg --verify software.sig software.tar.gz

Most open-source projects provide GPG signatures for their releases, which can be verified against their public keys. Check the project's official website for details.

For example, verifying a Arch Linux ISO download:

Download the public key:

gpg --recv-keys 3E80CA1A8B89F69CBA57D98A76A5EF9054449A5C

Verify the signature:

gpg --verify archlinux-2025.03.01-x86_64.iso.sig archlinux-2025.03.01-x86_64.iso

Conclusion

Online security is an ongoing effort. By using GPG for encryption and authentication, along with adopting strong security habits, you can significantly reduce your risk of data theft and surveillance. Stay informed, keep your software updated, and be cautious when sharing information online.

For further learning:

Coder Legion - Recent posts tagged using

How does SSH work and how can it be set up?

How SSH Works

1. The Handshake

2. Authentication

3. Encryption Layers

How to Setup SSH

Step 1: Install the SSH Server

Step 2: Generate SSH Keys (Recommended)

Step 3: Copy the Key to the Server

Step 4: Connect

Conclusion

How to Connect a DHT11 to a NodeMCU v2 board?

Hardware Check

Power Compatibility

Hardware Identification

Step-by-Step Wiring Guide

For the 4-Pin Bare Sensor

For the 3-Pin Module

Why the Pull-up Resistor Matters?

Coding Your DHT11 with PlatformIO

1. Configure platformio.ini

2. The Main Code (src/main.cpp)

Key Adjustments for the DHT11

Conclusion

Introduction to Go generics?

Why is Go Generics needed?

What is Go Generics?

Using Go Generics

Conclusion

HexmosTech / git-lrc

Free, Unlimited AI Code Reviews That Run on Commit

See It In Action

Why

Using the Internet Securely

Understanding GPG/PGP Keys

Generating a GPG Key

Encrypting and Signing Messages

General Internet Security Practices

Use Strong, Unique Passwords

Secure Your Email and Communications

Keep Software Updated

Browse the Web Safely

Verify Software Integrity

Conclusion

1. Configure `platformio.ini`

2. The Main Code (`src/main.cpp`)