What is secret/symmetric cryptography?
Secret key (symmetric/conventional) cryptography is a system based on the sender and receiver of a message knowing and using the same secret key to encrypt and decrypt their messages. One weakness of this system is that the sender and receiver must trust some communications channel to transmit the secret key to prevent from disclosure. Example: You use a strongbox to send a valuable gift to your friend, locking it with a key. No one can get to the gift without the key, including your friend. Your lock uses a symmetric key: the same key used to lock the box must be used to unlock it. Problem: you must find some method to deliver the key safely to your friend.
