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A digital signature is a cryptographic method to verify a digital document's authenticity, integrity, and the sender's non-repudiation using public key cryptography. It involves creating a unique "fingerprint" (hash) of the document, which the sender encrypts with their private key; this encrypted fingerprint, the signature, is attached to the document and can be decrypted by the recipient using the sender's public key to confirm the document hasn't been altered and was indeed sent by the claimed sender.

How It Works

Hashing: The sender's software creates a unique cryptographic hash (a fixed-size digital "fingerprint") of the document's content.

Encryption: The sender encrypts this hash using their private key. This encrypted hash is the digital signature.

Attachment: The digital signature is then appended to the original document.

Verification: The receiver's software decrypts the digital signature using the sender's public key to retrieve the original hash. The software then creates a new hash from the received document. Finally, it compares the two hashes; if they match, the document is confirmed to be authentic (from the sender) and untampered with (integrity).