[Cryptography] Hash Password, Nonce

(1) Hashed Password

stored hashed password H(p)in the Database, instead of plaintext password

use random number,called SALT (salt), together with P to add in the hash function.

(2) Nonce

1. Man in the middle(Modify)
2. Reply(retransmit)

1. Nonce to prevent Replay
random number, just used once
ensure the messages are fresh

2. Timestamp to prevent Man in the middle
require synchronized clocks
means limited time to do something