Hash Chain: understand each SHA-256 pass

Applying SHA-256 three times does not automatically create a stronger security property. For a tamper-evident sequence, define each link as a domain label, sequence number, canonical record and previous digest, then preserve a trusted initial anchor. Verification must check order and every intermediate link. If an attacker can replace both records and digests, use a keyed MAC or digital signature. Passwords require a salted password-hashing function; repeated fast hashes remain unsuitable regardless of iteration count.