Why Passwords Need Hashing

NEVER store passwords in plain text. When the database leaks (and it will), every account is compromised AND the same password is likely used elsewhere.

Solution: store HASHES of passwords. To verify: hash the input; compare to stored.

Naive: SHA-256(password). PROBLEM: too fast.

Modern GPUs compute BILLIONS of SHA-256 hashes per second. With a leaked database, an attacker tries every common password, dictionary, and rainbow tables. Most users' weak passwords crack in seconds.

Fix: use a SLOW hash. We DELIBERATELY waste CPU/memory so each guess costs more.

Targets:

• A login should take ~250ms (acceptable UX)
• An attacker brute-forcing 1B passwords takes ~1B * 250ms = 8 years (vs minutes with SHA)

The slow hash function families: bcrypt, scrypt, argon2.