Cryptography is the science of encoding a note into a form that's unreadable and making sure only the correct persons can handle decoding the message back to its original kind. This is often done through the use of an encryption algorithm and a decryption algorithm (both of these are often the same) and incredibly ordinarily a secret key. A few of the early cryptographic systems didn't use an integral but instead kept the algorithm itself top secret. The concept sender uses the encryption algorithm and the main element to encode the concept, and sends it to the receiver. The receiver in that case uses the decryption algorithm and the main element to carefully turn back the encrypted concept into its original contact form and read it.
If the message is intercepted others, they'll only have unreadable info and will have gained nothing, unless they are able to find out the decryption algorithm and obtain the main element. This is why the main element is to never be sent with the message, and must be kept secret by any means. If the main element is compromised, the sender and the encrypted info is no more safe. The sender and the receiver in that case usually acknowledge a new key to avoid any more damage.
In ancient Greece, around 550 Bc, text messages were dispatched encoded to generals and may only be decoded using unique staff keys. The main element actually contains a physical object, that was applied on the communication to get the decrypted edition of it. In 50 Bc., the most simple cryptographic algorithms ever before used was the main one called the Caesar cipher, that was employed by Julius Caesar to give messages to