Question

A "Digital Signature" provides which of the following security services?

• A. Confidentiality and Privacy
• B. Authentication and Non-repudiation
• C. Availability and Auditing
• D. Encryption and Compression

Hint:

Digital Signatures = A.I.N. (Authentication, Integrity, Non-repudiation). They do NOT provide confidentiality unless combined with standard encryption.

Answer 1

The Correct Option is B

Concept:
A digital signature is a mathematical technique used to validate the authenticity and integrity of a digital document, message, or software. It is the digital equivalent of a handwritten signature or a stamped seal, but it is much more secure.

Step 1: The Triple Pillars of Digital Signatures.
A digital signature provides three core security services:
• Authentication: It confirms that the message was indeed created by the person who claims to have sent it.
• Integrity: It ensures that the message has not been altered in transit (even a 1-bit change would cause the signature verification to fail).
• Non-repudiation: The sender cannot later deny having sent the message, because only they possess the private key used to create that specific signature.

Step 2: The absence of Confidentiality.
It is a common misconception that digital signatures provide confidentiality (privacy). By itself, a digital signature does not hide the content of the message; it only proves who sent it and that it wasn't changed. To achieve confidentiality, the message must be encrypted separately.

Step 3: Mechanism.
The sender creates a hash (digest) of the message and encrypts that hash with their Private Key. The recipient decrypts the hash using the sender's Public Key and compares it to a locally calculated hash. If they match, the identity and integrity are proven.