Salts

A salt is a random value mixed into the hash:

hashed = hash(salt || password)

Why? Without salt:

• Two users with the same password have the same hash.
• Attackers can precompute hashes of common passwords (rainbow tables).
• One leak compromises every "password123" account immediately.

With salt:

• Each user's hash is different even for the same password.
• Attackers must brute-force EACH ACCOUNT individually — 100M users = 100M separate attacks.

Salt requirements:

• Random (use CSPRNG, not Math.random)
• Unique per password (NOT a global salt)
• Stored alongside the hash (not secret — just unique)
• At least 16 bytes

Storage format (typical):

$2b$12$abc...salt22chars$hashOfPassword31chars
 |   |  |---salt---||---hash---|
 alg cost

bcrypt encodes everything in this format. argon2 is similar with more fields.