Digital Signatures

A digital signature is a cryptographic mechanism that provides authentication, integrity, and non-repudiation for digital documents, messages, and transactions. It is the digital equivalent of a handwritten signature — but far more secure and verifiable.

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What Digital Signatures Provide

Property	Description
Authentication	Confirms the identity of the signer
Integrity	Proves the message has not been altered since signing
Non-repudiation	The signer cannot deny having signed the document

Note: Digital signatures do not provide confidentiality — the message itself is not encrypted. Use encryption separately if confidentiality is required.

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How Digital Signatures Work

Signing Process

1. Hash the message:       digest = SHA-256(message)
2. Sign the hash:          signature = Encrypt(digest, signer's PRIVATE key)
3. Send:                   message + signature + signer's certificate

Verification Process

1. Hash the received message:   digest₁ = SHA-256(received message)
2. Decrypt the signature:       digest₂ = Decrypt(signature, signer's PUBLIC key)
3. Compare:                     if digest₁ == digest₂ → signature is VALID
                                if digest₁ != digest₂ → signature is INVALID