What is the significance of the hash in digital signatures?

• A. It encrypts the document for confidentiality.
• B. It ensures that the document content has not been altered.
• C. It verifies the sender's identity.
• D. It provides non-repudiation of the signature.

Answer: (B)

In digital signatures, the hash is used to ensure integrity by converting the document into a fixed-size digest that is signed with the signer’s private key. The signer creates a hash of the message and then signs that hash. When verifying, the recipient decrypts the signature with the signer’s public key to recover the hash and independently hashes the received document. If both hashes match, it shows the content hasn’t been altered since it was signed. This is why the hash’s significance is about maintaining integrity and detecting any modification.

Confidentiality isn’t provided by the hash or the signature process itself, so encrypting the document for confidentiality isn’t the role of the hash. Verifying the sender’s identity and non-repudiation are achieved through the use of the signer’s private/public key pair and the signature as a whole, not by the hash alone.