What is a digital signature?

A digital signature is fundamentally a cryptographic mechanism that ensures the authenticity and integrity of a message or transaction. It utilizes public-key cryptography to create a unique signature for each document or message, which can be verified by anyone with access to the signer's public key. This process guarantees that the sender cannot deny having sent the message (non-repudiation) and that the message has not been altered in transit.

The significance of a digital signature lies in its ability to provide trust in digital communications and transactions. For instance, in blockchain technology, digital signatures are crucial for verifying transactions, ensuring that only authorized parties can initiate them and that the data has not been tampered with. By employing this mechanism, digital signatures facilitate secure and reliable interactions in various applications, including smart contracts and financial transactions.

The other options do not accurately describe what a digital signature is, thereby reinforcing that the correct choice involves the validation of authenticity and integrity through cryptographic means.