There are plenty of ciphers and basic forms of early cryptography that existed in the past. One of those ciphers is the null cipher, also known as the concealment cipher. This particular cipher is interesting because it is also seen as an early simple form of steganography: the practice of hiding a message or information from prying eyes by hiding one message within another message or a physical object that looks far more inconspicuous than what is actually being communicated between different people.
It was created with the intention of confusing the average cryptanalyst - a person whose job it is to analyze information and messages specifically to look for some kind of hidden messaging that could be available. It was common to do things where some degree of the plaintext and the actual message is disguised in the ciphertext, and a person would need to discard certain ‘null’ unnecessary letters used to hide the real message to find out what the people communicating with one another are actually try to tell each other. There are plenty of examples of this cipher actually being utilized in the real world in the past, such as one example of a message that was used by the German military back in the First World War that is a good basic display of the null cipher:
PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE. GRAVE SITUATION AFFECTING INTERNATIONAL LAW. STATEMENT FORESHADOWS RUIN OF MANY NEUTRALS. YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY. - German military message during World War I
This particular cipher reveals the true message the German army wanted to communicate if you take the first letter of every single word in order to reveal the hidden message Pershing sails from N.Y. June I. For those who need a reminder of history, John Joseph Pershing was a senior US Army Officer who fought in the First World War, and this message was from the German military telling other members of the German armed forces how this man would be arriving in New York City on June 1st.
Null ciphers go back even farther back than the First World War and can be found back during the English Civil War - a war between the people who wanted a parliament and the people who wished to reestablish an absolute monarchy and have England return to authoritarian rule under a hereditary leader. Here is a null cipher that was sent to Royalist Sir John Trevanian to escape from a Puritan castle:
WORTHIE SIR JOHN, HOPE, THAT IS YE BESTE COMFORT OF YE AFFLICTED, CANNOT MUCH, I FEAR ME, HELP YOU NOW. THAT I WOULD SAY TO YOU, IS THIS ONLY: IF EVER I MAY BE ABLE TO REQUITE THAT I DO OWE YOU, STAND NOT UPON ASKING ME. TIS NOT MUCH THAT I CAN DO; BUT WHAT I CAN DO, BEE YE VERY SURE I WILL. I KNOW THAT, IF DETHE COMES, IF ORDINARY MEN FEAR IT, IT FRIGHTS NOT YOU, ACCOUNTING IT FOR A HIGH HONOUR, TO HAVE SUCH A REWARDE OF YOUR LOYALTY. PRAY YET YOU MAY BE SPARED THIS SOE BITTER, CUP. I FEAR NOT THAT YOU WILL GRUDGE ANY SUFFERINGS; ONLY IF BIE SUBMISSIONS YOU CAN TURN THEM AWAY, TIS THE PART OF A WISE MAN. TELL ME, AN IF YOU CAN, TO DO FOR YOU ANYTHINGE THAT YOU WOLDE HAVE DONE. THE GENERAL GOES BACK ON WEDNESDAY. RESTINGE YOUR SERVANT TO COMMAND.
If you look at every third leader after each form of punctuation, you would see the message “Panel at East side of Chapel slides.”
Eventually, this particular cipher fell out of disuse, and that is why it is considered classical encryption: encryption that has generally fallen out of disuse unless it is combined with other, more secure forms of encryption. That being said, it is still a decent encryption code for the time and one of the earlier forms of steganography before that became a stable of encryption and cryptographic practices!