What best defines a digital signature?

A digital signature is best defined as a cryptographic value that validates a sender's identity and message integrity. This process involves using cryptographic algorithms to create a unique code that is attached to a digital message or document. This code verifies that the message was indeed sent by the claimed sender and that it has not been altered in transit. When a recipient receives a digitally signed message, they can use the sender's public key to confirm the signature, thereby ensuring both the authenticity of the sender and the integrity of the message content.

The other options do not accurately capture the essence of a digital signature. For instance, while data encryption may be involved in securing communications, it does not specifically validate the identity of the sender or guarantee message integrity. Email verification processes are typically simpler and don't involve the advanced cryptographic methods used by digital signatures. Lastly, while a coding system for managing online transactions may involve various security measures, it does not specifically define the purpose and functionality of a digital signature.