Hashing, Digital Signatures, Blockchain & Certificates

What is the primary purpose of a cryptographic hash function, and what are its key properties?

To convert data of any size into a unique, fixed-size string (digest) to ensure data integrity. Key properties include being one-way (irreversible) and collision-resistant (two different inputs cannot produce the same hash).

What is the security difference between an HMAC and a standard hash?

An HMAC (Hash-based Message Authentication Code) combines a cryptographic hash function with a secret shared key, providing both data integrity and authentication (verifying the sender's identity).

What two security properties does a Digital Signature provide that a simple hash does not?

• Authentication: Proves the exact identity of the sender.

• Non-repudiation: Ensures the sender cannot deny having sent the message (because it was encrypted with their unique private key).

What is the primary security benefit of Blockchain / Distributed Ledger Technology (DLT)?

• Immutability and decentralization. Because every block contains a cryptographic hash of the previous block across multiple nodes, past transactions cannot be altered without breaking the entire chain.

What is a Smart Contract in a blockchain environment?

Self-executing code stored on a blockchain that automatically triggers and enforces contract terms the moment predefined conditions are met, eliminating the need for a trusted intermediary.

What is the purpose of a Certificate Signing Request (CSR)?

A file sent by an applicant to a Certificate Authority (CA) containing their public key and domain details to request a digital certificate. (Note: The local private key never leaves the server and is never in the CSR).

What does the Subject Alternative Name (SAN) extension do in a digital certificate?

It allows a single digital certificate to secure multiple completely different domain names, subdomains, or IP addresses on a server.

Why would a web browser throw an "Untrusted Connection" error when visiting a secure site, even if a valid end-entity certificate is installed?

Because the server is missing the intermediate and root CA certificate chain bundle, breaking the cryptographic path of trust back to a trusted root authority.