Which statement about digital signatures is true?

• A. A digital signature cannot be moved from one signed document to another because it is the hash of the original document encrypted with the private key.
• B. A digital signature provides confidentiality.
• C. A digital signature is created by symmetric key encryption.
• D. A digital signature is interchangeable among documents.

Answer: (A)

Digital signatures bind the signer to the exact content of a document. They are created by hashing the document and encrypting that hash with the signer's private key. Verification uses the corresponding public key to decrypt the signature and compare it to a fresh hash of the received document. Because the signature depends on the document’s specific content, it won’t validate for a different document—the hash would be different and the verification would fail. This is why a digital signature cannot be moved from one signed document to another. Also, remember that digital signatures do not provide confidentiality—they assure authenticity and integrity (and non-repudiation) using asymmetric cryptography, not symmetric, and the signature is inherently tied to the particular document content, even if the same private key is used for multiple signatures.