A web application requires users to register before they can use its services. Users must choose a unique username and a password that contains a minimum of eight characters. Which method MUST be used

Encryption is reversible, meaning if the master or per-user key is compromised, all passwords are immediately exposed in plaintext, which does not provide adequate protection for stored credentials.

A fast hash function (such as MD5 or SHA-256) with a salt prevents rainbow table attacks but remains highly vulnerable to offline brute-force attacks because an attacker can compute billions of hashes per second with commodity hardware.

A hash function with a cost factor (such as bcrypt, scrypt, or Argon2) is specifically designed to be computationally slow and memory-intensive, making offline brute-force attacks extremely expensive even with modern hardware. The cost factor can be increased over time as hardware improves, maintaining resistance to attacks. The per-user random salt ensures that identical passwords produce different hashes, preventing rainbow table and batch-cracking attacks.

Encryption with a random master key is reversible and stores a single key that, if compromised, exposes all passwords simultaneously, providing no meaningful resistance to offline attacks once the key is obtained.