A perfectly good book for children about codes, cyphers, and ancient or unusual languages. Most code ideas get a two-page spread with text and illustration; some get twice as much. The book is 64 pages, and just about square.

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Detailed Review:
The Scytale - mechanical aid for transposition cypher. We imagine an m-by-n matrix, A, where m is the number of rows, determined by the width of the stick, while n is the number of windings of the leather strip around the stick. The choice of the leather strip can determine n as the strip may be narrower, thus fitting more columns onto the stick, or it may be shorter, affording length for fewer columns. The height of the characters determines m. The message is written out row-by-row. The message is mechanically encoded by the strap. The encrypted result is essentially the rows in order of A transpose. The decryption is simply to transpose the matrix again. The message may start at any row. The difficulty is knowing m and n, without the key, i.e., the scytale. There is a reasonable discussion of the mathematics of this thing in http://pi.math.cornell.edu/~mec/2003-2004/cryptography/transposition/transpositi.... Another good discussion can be found here: http://users.etown.edu/m/mcdevittt/CryptoNotes.pdf. Ultimately, though, it's an analog encryption device, and so it starts to seem rather boring to me.

The Pigpen Cypher - a simple substitution cypher w/ funny symbols. Pretty uninteresting.

A letter within a letter - steganography

The Polybius Square - Another simple substitution cypher, seems more like morse code, but for torches.

Caesar's Secrets - Another simple substitution cypher, attributed, probably incorrectly, to Caesar.

ZigZag Writing - A relocation cypher. The one zigzag version is much simpler than the scytale. Let the characters be represented as c_0, c_1, ..., c_n. Then the first chunk contains all characters such that i % 2 = 0 for any c_i, the second chunk contains all characters such that (i + 1) % 2 = 0. Keep them sorted, and they are encrypted. You could compute all this by using two queues, and shoving characters on the queues alternately. To decrypt, you remove from your two queues alternately. Alternatively, you compute the location of the character from its tuple index. The encrypted version is c_(0,0), c_(0,1), ..., c(0, p), c(1, 0), ..., c(1, q) where p = q or p = q + 1. To decrypt, calculate the index as f(i, j) = i + j * 2. It is easy to identify the boundary between the first and the second chunk in a two way zigzag, so this is easy to decrypt.

Spies and Buried Treasure - book codes and Benedict Arnold

Pig Latin - A spoken code. It is streamed, as it were, so if it spoken fast and crisply others will fail to understand and the encrypted text will be lost to them. If recorded, of course, that is another matter.

Language as Code - Hieroglyphs decoded by the Rosetta Stone. Etymology - "sacred carving".

Morse Code - Not for encryption, but based on frequency of letters. Morse studied up on letter frequency to design his code. In another book, I read that encryption soon followed, because anybody could listen in.

High Seas Code - Nautical signaling flags

Semaphore - etymology "sign bearing" it is about the placement of the flags, not what is on them.

Reading Between the Lines: Word size Grilles. Practically these seem like they would have been tricky. It would be hard to make the rest of the writing look natural.

Supersecrets - Using some form of double encryption
This is not that interesting, since the individual cyphers are so simple and, essentially, known.

The Knocking Nihilists - knocking code, for prisoners

Thomas Jefferson's Cipher
TJ invented a mechanical cypher wheel. If you have the cypher wheel you can decrypt the message. Each character is encrypted with a different cypher, but the offset is always the same. Not particularly resistant to frequency analysis as the offset may be reused, so probably more or less equivalent to the Vigenere cypher, in the end.

Cipher Disk
A mechanical disk that can be used to implement the Vigenere Cipher. These ciphers were at first quite resistant to frequency analysis, until sophisticated methods of frequency analysis were introduced by Charles Babbage and others. It is very similar to the TJ, except more simple, since every character is encrypted by a related cipher making it more susceptible to frequency analysis.

The Turning Grille
Another kind of grille, for individual characters. The example used is a six-by-six inch grid with 9 apertures. The grille is turned four times, each time exposing a new set of letters. Decrypting involves reading the letters through the grille. This was used up until WWI. For ease of use it is necessary that no aperture will be placed over the same square twice. This condition requires that the size of the square must be even, as if the it were odd, then the center square would always end up over the same spot. Of course, you could always fill the center square with a null. 6 * 6 = 4 * 9 = 36, so after 4 turns, every square in the grid has been filled. The interesting mathematical question is: how do you select the 9 apertures so that they do not overlay the same space twice? Well, you randomly select one, then you cross out all the other ones that it could overlay by rotation, of which there are three due to the 4 possible positions. So, it turns out that the number of possible aperture arrangements in an n-by-n square is (n^2/4)! For a 6-by-6 square, thats 9! = 362880. Not too bad. It's not clear at all how that affects the difficulty of decryption, of course. The Fleissner Grille is simply printed with the digits in their possible places. So, on a 6-by-6 grid the numbers 1 through 9 would be printed in a systematic fashion, with 1 in 4 places respecting the places it could occupy for all 4 rotated positions. Then, the user would select a 1 from the 4 possible places, a 2, and so forth, through 9.

The Enigma Machine
A bit of a muddled explanation.

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To sum up --- a little bit disorganized, but fun. ( )