A digital signature is a cryptographic technique used to verify the authenticity, integrity, and origin of digital data—like documents, emails, or software.

🔐 What Is a Digital Signature?

A digital signature is like a virtual fingerprint:

• It confirms that the data was created by a known sender (authenticity).
• It ensures the data hasn’t been altered in transit (integrity).
• It prevents the sender from denying they sent it (non-repudiation).

🧪 How It Works

Here’s a simplified breakdown of the process:

1. Hashing the Data

   • A hash function converts the original message into a fixed-length string (digest).
   • This digest is unique—any change in the message alters the hash.

2. Signing the Hash

   • The sender encrypts the hash using their private key.
   • This encrypted hash becomes the digital signature.

3. Sending the Message

   • The original message and the digital signature are sent together.

4. Verifying the Signature

   • The receiver decrypts the signature using the sender’s public key.
   • They hash the received message and compare it to the decrypted hash.
   • If they match, the message is verified.

🛡️ Key Benefits

🧰 Real-World Uses

• Secure email communication
• Software distribution
• Online banking
• Electronic document signing (e.g., contracts, PDFs)

🏛️ Certificate Authorities (CA)

Digital signatures rely on certificates issued by trusted entities called Certificate Authorities. These certificates link a public key to a verified identity—like a driver’s license for the digital world.