Cryptography

Cryptography is the method for distorting plain text so that it is unreadable by someone other than the intended recipient. For example, someone that is using a packet sniffer (see bpf) to listen in on network connection. Only if this third party knows the secret key to the ciphertext will they break the encryption and be able to see the plaintext. Anyone using plain text protocols these days is as stupid as sshd is free.