A null cipher, also known as concealment cipher, is an ancient form of encryption where the plaintext is mixed with a large amount of non-cipher material. Today it is regarded as a simple form of steganography, which can be used to hide ciphertext. This is one of 3 categories of cipher used in classical cryptography along with Substitution ciphers and Transposition ciphers. Classical cryptography In classical cryptography, a null is intended to confuse the cryptanalyst. In the most common form of a null cipher, the plaintext is included within the ciphertext and one needs to discard certain characters in order to decrypt the message (such as first letter, last letter, third letter of every second word, etc.) Most characters in such a cryptogram are nulls, only some are significant, and some others can be used as pointers to the significant ones. Here is an example null cipher message, sent by a German during World War I: Taking the first letter of every word reveals the hidden message "Pershing sails from N.Y. June I". Here is a more complicated example from England's Civil War which aided Royalist Sir John Trevanian in his escape from a Puritan castle in Colchester: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.The third letter after each punctuation reveals "Panel at East side of Chapel slides". A similar technique is to hide entire words, such as in this seemingly innocent message written by a prison inmate but deciphered by the FBI: Taking only every fifth word, one can reconstruct the