🧐 What is a Digital Signature?

A digital signature is a cryptographic technique that ensures the authenticity, integrity, and non-repudiation of digital messages or documents.

When you digitally sign a document, you are providing a unique fingerprint that proves:
✔ The message is from you (Authentication).
✔ The message was not altered in transit (Integrity).
✔ The sender cannot deny signing it (Non-Repudiation).

🔑 How Do Digital Signatures Work?

A digital signature is created using asymmetric encryption (Public Key Cryptography). It involves:
1️⃣ Hashing the message (to create a unique fingerprint).
2️⃣ Encrypting the hash with the sender’s private key.
3️⃣ Sending the message & signature to the receiver.
4️⃣ Verifying the signature using the sender’s public key.

sequenceDiagram
    participant Sender as 🟢 Sender
    participant Receiver as 🔵 Receiver

    Sender ->> Sender: Hash the Message 🔢
    Sender ->> Sender: Encrypt Hash with Private Key 🔑
    Sender -->> Receiver: Send Message + Digital Signature 📜

    Receiver ->> Receiver: Decrypt Signature with Public Key 🔓
    Receiver ->> Receiver: Hash the Received Message 🔢
    Receiver -->> Receiver: Compare Hashes ✅

    Note right of Receiver: If hashes match, the message is authentic! 🔏

📌 Step-by-Step Breakdown of Digital Signature Process

1️⃣ Message Hashing:

• The sender applies a hashing algorithm (e.g., SHA-256) to the original message.

• This creates a fixed-length unique hash (fingerprint).

2️⃣ Signing the Hash:

• The sender encrypts the hash using their private key.

• This encrypted hash becomes the digital signature.

3️⃣ Message Transmission:

• The original message + digital signature are sent to the receiver.

4️⃣ Signature Verification:

• The receiver decrypts the signature using the sender’s public key.

• The receiver hashes the received message using the same algorithm.

• If the hashes match, the message is authentic and unchanged!

🔍 Why Use Digital Signatures?

✅ Prevents Tampering – Ensures the message wasn’t altered.
✅ Proves Authenticity – Verifies the sender’s identity.
✅ Ensures Non-Repudiation – The sender cannot deny sending the message.

🔹 Digital Signatures vs Electronic Signatures

📌 Digital Signatures are cryptographically secured, whereas Electronic Signatures are often just images of handwritten signatures.

🌍 Where Are Digital Signatures Used?

📌 Software Distribution – Ensures apps & updates come from a trusted source.
📌 Secure Email (PGP, S/MIME) – Verifies sender authenticity.
📌 Blockchain & Cryptocurrency – Used for secure transactions.
📌 Legal Documents (e.g., DocuSign) – Provides legal validity.

🛠️ How to Create a Digital Signature in Node.js?

Want to see a digital signature in action? Here’s an example using RSA encryption in Node.js with the built-in crypto

const crypto = require('crypto');

// Generate RSA Key Pair
const { publicKey, privateKey } = crypto.generateKeyPairSync('rsa', {
  modulusLength: 2048,
});

// Original Message
const message = "Secure Message";

// Create Digital Signature
const sign = crypto.createSign('SHA256');
sign.update(message);
sign.end();
const signature = sign.sign(privateKey, 'hex');

console.log("Signature:", signature);

// Verify the Signature
const verify = crypto.createVerify('SHA256');
verify.update(message);
verify.end();

const isValid = verify.verify(publicKey, signature, 'hex');
console.log(isValid ? "✅ Signature is valid!" : "❌ Signature is invalid!");

This Node.js script:
✅ Generates RSA key pairs
✅ Creates a digital signature for a message
✅ Verifies the signature using the public key

🚀 Final Thoughts

Digital Signatures are essential for security, providing:

• Authenticity – Verifies the sender.

• Integrity – Ensures data wasn’t altered.

• Non-Repudiation – The sender cannot deny signing.

Would you like a tutorial on how to implement digital signatures in AWS KMS or OpenSSL? Let’s discuss in the comments! 👇

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About Me 👨‍💻

I'm Faiz A. Farooqui. Software Engineer from Bengaluru, India.
Find out more about me @ faizahmed.in