[2] Here is an example null cipher message, sent by a German during World War I:[3] PRESIDENT'S EMBARGO RULING SHOULD HAVE IMMEDIATE NOTICE.
YELLOW JOURNALS UNIFYING NATIONAL EXCITEMENT IMMENSELY.Taking the first letter of every word reveals the hidden message "Pershing sails from N.Y. June I".
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.
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:[5]
For example, Cardinal Richelieu is said to have used a grille to write secret messages, after which the blank spaces were filled out with extraneous matter to create the impression of a continuous text.
The acrostic puzzle is an extended form of null cipher, but not an anacrostic (which uses a set of lettered clues with numbered blanks representing the letters of the answer to figure out the second part, a long series of numbered blanks and spaces representing a message into which the answers for the clues fit).
For example, Rolfe Humphries received a lifelong ban from contributing to Poetry Magazine after he wrote and tried to publish "a poem containing a concealed scurrilous phrase aimed at a well-known person", namely Nicholas Murray Butler.
[2] In general, it is difficult and time-consuming to produce covert texts that seem natural and would not raise suspicion, but a null cipher is an option if one is unable to use an advanced encryption method and has ample time.
If no key or additional encryption is involved, the security of the message relies entirely on the secrecy of the concealment method.