Digital Signature

A digital signature is a cryptographic technique that ensures:

• Authenticity – verifies the sender’s identity
• Integrity – confirms that the message has not been altered
• Non-repudiation – the sender cannot deny sending the message

It is the digital equivalent of a handwritten signature or stamped seal, but much more secure and verifiable through public-key cryptography.

How Digital Signatures Work

Based on Asymmetric (Public Key) Cryptography

Each user has:

• A private key (kept secret)
• A public key (shared with everyone)

Signing Process

1. Sender creates a message.
2. Computes the hash of the message.
3. Encrypts the hash using their private key → digital signature
4. Sends the message + signature to the receiver.

Verification Process:

1. Receiver receives the message and digital signature.
2. Computes the hash of the message.
3. Decrypts the signature using sender’s public key.
4. If the two hashes match → message is authentic and unchanged.

Uses of Digital Signature

Feature	Benefit
Message Integrity	Detects tampering
Authentication	Confirms sender identity
Non-repudiation	Prevents sender from denying the message
Trust Establishment	Enables secure communication

Workflow of Digital Signature

+-----------+             +-------------------+             +-------------+
|   Client  | -- Sign --> |   Send Message    | --> Verify →|   Server    |
+-----------+             +-------------------+             +-------------+
     |                             |                                |
     |-- Private Key --(hash & sign)--->              -- Public Key -->
     |                             |                                |
Message + Signature       →        API Gateway        →     Validated