Crypto
You already know that you should never roll out your own crypto.
Password Hashing (One-way Key Derivation Functions)
The hash may follow a scheme which encodes the KDF, for example $method$params$salt$hash.
- 2018 state-of-the-art: Argon2 (not standardised yet).
- CPU, Memory, Parallelism-hard
- Scrypt
- Bcrypt
- PBKDF2
Passwords are low-entropy data; you need to slow down attackers with access to vash parallel computation.
Cryptographic Hashing
Designed to be fast while guaranteeing no collisions and no way of reversing the hash.
These are suitable for file integrity, message authentication, inputs for cryptographic signatures.
There is yet another category of hasing functions used for dictionaries/hash tables :)
2FA/TOTP/U2F
Entropy
Entropy is calculated using the password-generation function, not the password!