Shinobi iroha is a special code which the ninja used. They used the code starting from [i], finishing with [n], 48 letters in total, including the letters [wi] and [we].
They used characters that looked like kanji (Chinese characters) each corresponding pending to a phonetic sound. When the ninja sent encrypted letters, the code was usually sent in advance in a separate correspondence.
However, when the code could not be sent in advance, secret messages were written in normal letters but the delivery man was extra careful. In that case messages were divided into three pieces and delivered by three different ninja.
Handwriting was changed and they didn’t use habitual words. Secret messages were usually hidden inside of the ninja’s hat,but were sometimes tied up in their hair, or hidden in the collar of their kimono. Ninja tried to keep secret messages close to their bodies.
Sometimes ninja hid messages in an egg shell or walnut shell so an enemy would never find the secret messages.
In order to keep trade of time, ninja usually carried hourglasses, but they also had other methods of telling time. Cat's eye watches were a method of telling time by looking at how widely a cat's eyes were opened. Cats eyes (the pupil) were widely open at dawn, sunset and at 6 in the morning.
At eight in the morning and 4 in the evening, their eyes were oval shaped and narrow.
At 10 in the morning and 2 in the afternoon the oval became narrower, about the size of a kaki (Japanese persimmon)seed. Right at noon, a cat’s eyes became even narrower, like a needle. Ninja knew how to tell the time by looking at a cat’s eyes and used this knowledge often. Ninja learned martial arts, knew how to make gunpowder, learned astronomy, studied the flora and fauna, they had knowledge in many different fields.