It is simply a matter of inspection to read a message in a cipher of this type, once the dimensions of the rectangles have been determined. We place the whole or a portion of the message in such rectangles and read horizontally, vertically and diagonally forward and backward. Parts of words will at once be apparent and the whole message is soon deciphered. Two examples will show the process.
Message
ILVGIOIAEITSRNMANHMNG
This message contains eight vowels or 38% out of twenty-one letters, and the letters LNRST occur 7 times or 33%, the letters XQJKZ not appearing. It is therefore a transposition cipher. Twenty-one letters immediately suggest seven columns of three letters each or three columns of seven letters each. Trying the former we have:
| I L V G I O I |
| A E I T S R N |
| M A N H M N G |
and reading down each column in succession ([Case 1-b]) reveals the message to be “I am leaving this morning.”
Message
| M S I B R | O R S E E | V U E E M | C O R E R | E L I D E | T O E P Q |
| E N R E R | N S E R Y | E C O L L | E R E U S | P L U R C | E L O A J |
| A E H U H | P F A S O | N N O A A | E P I U A | P P E A C | U Q A R U |
| O P O E I | I R R M I | A F D A A | R Q U B O | Z A E G E | R S F S X |
There are 120 letters in this message with 57 vowels or 47% vowels, and the letters LNRST occur 31 times or 26% of the whole.
Non-occurrence of K and W and vowel proportion leads us to the assumption that it is a transposition cipher of a Spanish text. The factors of 120 are 5 × 3 × 2 × 2 × 2. We may then have one rectangle of 4 × 30 or one of 5 × 24 or two of 5 × 12, or three of 5 × 8, or four of 5 × 6, or five of 3 × 8, or ten of 3 × 4, or twenty of 3 × 2. The message being in a rectangle of 4 × 30, we can inspect it as it stands and this is clearly not the arrangement if it be a geometrical transposition cipher at all. It is best however to try the largest possible rectangles first so we will put it in the form 5 × 24, thus: