Javascript firma: Digital Signatures

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Jake Colins

Imagine you’re sending a secret message. You want to make sure it wasn’t changed by anyone on the way. How do you do that on the web? That’s where digital signatures come in! And guess what? You can do it using simple JavaScript.

TL;DR (Too long, didn’t read)

Digital signatures are like wax seals on digital messages. They prove a message came from the sender and hasn’t been changed. In JavaScript, you can use libraries like Web Crypto API to create and verify these signatures. It’s a handy way to build trust into your apps!

What is a Digital Signature?

A digital signature is like a handwritten signature—but for digital files and messages. It helps prove two things:

  • Authenticity – You know who sent it.
  • Integrity – You know it wasn’t changed.

Let’s say Alice sends a signed message to Bob. Bob can check the signature and be sure it really came from Alice. And that no hacker edited the message. Pretty cool, right?

How Does It Work?

Digital signatures use some fancy math involving public-key cryptography. But don’t worry, we’ll keep it light!

  1. Alice has two keys: a private key and a public key.
  2. She writes a message and signs it using her private key.
  3. She sends the message and her signature to Bob.
  4. Bob verifies the signature using Alice’s public key.

If everything checks out, Bob knows the message is real and untouched.

Can JavaScript Do This?

Yes! The modern web gives us a tool called the Web Crypto API. This is a set of methods built into the browser for things like encryption, hashing, and signing.

It’s all done without needing any extra libraries or plugins. Just pure, browser-powered JavaScript.

Your First Digital Signature in JavaScript

Let’s walk through a simple example. Don’t worry, we’ll go step-by-step.

1. Generate a key pair

We need a public-private key pair for signing and verifying.


const keyPair = await window.crypto.subtle.generateKey(
  {
    name: "RSASSA-PKCS1-v1_5",
    modulusLength: 2048,
    publicExponent: new Uint8Array([1, 0, 1]),
    hash: "SHA-256"
  },
  true,
  ["sign", "verify"]
);

This gives us two keys we can use. One for signing, and one for verifying.

2. Sign a message

We’ll create a simple message and sign it.


const message = new TextEncoder().encode("Hello, world! I am Alice.");
const signature = await window.crypto.subtle.sign(
  "RSASSA-PKCS1-v1_5",
  keyPair.privateKey,
  message
);

Now we have a signed message. That’s like a secret stamp!

3. Verify the message

Now let’s verify it using the public key.


const isValid = await window.crypto.subtle.verify(
  "RSASSA-PKCS1-v1_5",
  keyPair.publicKey,
  signature,
  message
);

console.log(isValid);  // true if the signature is legit

If isValid is true, you know the message and signature match.

Why is This Useful?

You can use digital signatures in many cool ways:

  • Secure messages between people
  • Stop hackers from faking users
  • Make sure files weren’t modified
  • Prove ownership in content (like NFTs)

They’re like crystal-clear evidence on the web.

Common Terms You’ll Hear

Let’s break down some common words so you feel like a pro.

  • Signing – Creating a signature with a private key.
  • Verification – Checking a signature with a public key.
  • Hash – A summary of data, like a fingerprint.
  • Public-key cryptography – Math that uses key pairs.

Is It Safe?

If done right, yes! These digital signatures are based on strong encryption. Most are powered by algorithms like RSA and ECDSA. They’ve been tested for years.

Just make sure to store your private key safely and never share it!

Some JavaScript Libraries That Can Help

While Web Crypto API is great, some developers prefer libraries. You might try:

  • node-forge – A toolkit with crypto functions.
  • jsrsasign – Made for handling keys and signatures.
  • tweetnacl – A minimal, secure crypto library.

These can help if you’re working in Node.js or want more features.

Things to Watch Out For

Okay, a little word of caution!

  • Don’t generate weak keys.
  • Don’t share your private key. Ever.
  • Use HTTPS to prevent man-in-the-middle attacks.
  • Store your public keys safely too—if they’re changed, verification fails.

Use best practices and your digital signature system will stay rock solid.

Imagine This in Real Life!

Let’s say you’re building a safe chat app. Each user signs every message. The messages fly across the web. On the other end, the app verifies each message before it shows it.

If someone tries to send a fake message as another user, it will fail. That’s digital signatures for the win!

Or: you’re sending a contract. You digitally sign it with your private key. The receiver checks it using your public key and knows it’s really you. No faking allowed!

Final Thoughts

JavaScript makes it easy to use digital signatures with just a few lines of code. No magic—just modern browser tools and smart crypto math.

By learning this, you’re adding an important tool to your developer toolbox. Whether you’re building an app, a website, or a full platform—you can make it more trustworthy with signatures.

So go ahead—add digital wax seals to your code! 🕵️‍♂️⚙️