Editing Classical cipher (section)

=== Concealment ciphers ===
{{Main article|Null cipher}}

Put simply, a concealment, or null, cipher is any cipher which involves a number of ''nulls,'' or decoy letters. A null cipher could be [[plaintext]] words with nulls placed in designated areas or even a plaintext message broken up in different positions with a null at the end of each word.<ref name=":4">{{Cite book |last1=Travis |first1=Falcon |title=The Spy's Guidebook |last2=Hindley |first2=Judy |last3=Thomson |first3=Ruth |last4=Amery |first4=Heather |last5=Rawson |first5=Christopher |last6=Harper |first6=Anita |publisher=Usborne Pocketbooks |year=1978}}</ref><ref>{{Cite book |last=Moore |first=Gareth |title=Explorer Academy Codebreaking Activity Adventure |year=2019 |publisher=National Geographic Books |isbn=9781426333071}}</ref> However, a message with only a couple nulls (for example, one at the beginning and one at the end) is ''not'' a null cipher.

For example, during [[English Civil War|England's Civil War]]  Royalist Sir John Trevanian was aided in his escape from a Puritan castle in [[Colchester]] by this message:<ref name=":1">{{Cite book |last=Janeczko |first=Paul B. |title=Top Secret: a Handbook of Codes, Ciphers, and Secret Writing |publisher=Candlewick Press |year=2004 |isbn=9780763629724}}</ref><blockquote>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.</blockquote>The third letter after each punctuation reveals "Panel at East end of Chapel slides".

A dot or pinprick null cipher is a common classical encryption method in which dot or pinprick is placed above or below certain letters in a piece of writing.<ref name=":13">{{Cite book |last=Janeczko |first=Paul B. |title=Top Secret: a Handbook of Codes, Ciphers, and Secret Writing |publisher=Candlewick Press |year=2004 |isbn=9780763629724}}</ref> An early reference to this was when [[Aeneas Tacticus]] wrote about it in his book ''On the Defense of Fortifications.''<ref name=":3">{{Cite web |title=Aeneas Tacticus • Siege Defense, XXI‑XXXI |url=https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Aeneas_Tacticus/E*.html |access-date=2022-05-28 |website=penelope.uchicago.edu}}</ref>