Elementary cryptanalysis

The subject which we are about to study is the analysis and solution of _cipher_, though not including _code_, which is a very special form of cipher demanding something more th...

Concealment writing may take a host of forms. Perhaps its oldest known application is found in the ancient device of writing a secret message on the shaved head of a slave and d...

Transposition has already been explained as a form of cipher in which the letters of a message are disarranged from their natural order in accordance with any pattern, or key, a...

In the preceding chapter, we glanced at the most elementary form of _columnar transposition_: a text is written into a block by rows and taken off by columns in such a way that...

O E E H E A T F L S V A S Y C I O A E D Q O H D F M C M T C P O G E O R E U G M I E F U O G C Y W G D Q U U I A L S I E R N O R N R R A T O A Q.

The well-known _turning grille_, also known as the _rotating_, or _revolving_ grille, is said to have been originated by an Italian, Girolamo Cardano (or Cardan). Such grilles c...

Square units, in actual use, are less convenient than those rectangular encipherments in which only one dimension of the block is restricted, thus permitting that a single key g...

In the past few chapters, we have been looking at all of the general methods for decryptment of transpositions. We have seen the use of _factoring_, which determines, for the ge...

Substitution cipher presupposes the selection of a set of symbols which can represent the letters or words of messages. As to what these symbols may be, there is practically no...

Simple substitution is ordinarily defined as a cipher in which each letter of the alphabet has one fixed substitute, and each cryptogram-symbol represents one fixed original. Wh...

Several routine methods have been evolved for special use on the very difficult “aristocrat” — that fascinating form of simple substitution with word-divisions in which the mess...

Concerning the numberless variations and complications which have been applied to the simple substitution cipher, our discussion here will have to be along general lines, with p...

The theory of polyalphabetical substitution is as follows: The encipherer has at his disposal several simple substitution alphabets, usually 26. He uses one such alphabet to enc...

O S W I O S G Q I I. Part II: H H T X T N E O L V R M T U L C L P P X T Y R X K U K B U W U O J Z H X M Z K H. Part III: S Y Z Y R T N F U R K C U S I I R Q U X W U F K C J N R...

Now let us have a brief look at other classic ciphers of the multiple-alphabet type, and see to what extent these will differ from the Vigenère. The Gronsfeld cipher, as may be...

Prior to the 1860’s, the ciphers of the past two chapters had been regarded as entirely safe. A radical change of opinion took place in 1863, when Major F. W. Kasiski, a German...

When a Vigenère cryptogram is very short, its alphabets are no longer readily identified by their graphic appearance. But its period, in the majority of cases, can still be dete...

The term _autokey_ (_autoclave_; “the autokey cipher”), as commonly used, refers to the kind of encipherment shown in Fig. 116, in which a message becomes its own key for applyi...

The use of numbers in a periodic cipher does not, in itself, create a problem essentially different from that of the letter-ciphers. Numbers may, in themselves, cause weakness;...

Periodic cryptograms in which the cipher alphabets are mixed are nearly always produced by means of slides. Before discussing these ciphers, it may be well to clarify a few term...

YT A EL A CSNKZYCC B IUKLQIKT B OO C LE QK C FB DD D DD ZZUNZDZGDZ D BGAGYAGABB E RZPCJMAMZY E GAOFNIVUUS HJN F MVS F HUPSCCGCCWN G QDPKZOPQWKU G CK H SP H J I Q BB I CN LQBQ J...

Any one of the multiple-alphabet ciphers may change keys at each new group instead of with each consecutive letter. As a rule, this kind of encipherment is never found except in...

Before leaving the study of multiple-alphabet ciphers, we will consider briefly the process which, in its simplest form, would be that shown in Fig. 154. The initial key, in eac...

Polygram substitution contemplates the encipherment of several letters collectively: Digrams are to be replaced with other digrams, or with three-digit numbers; trigrams are to...

Fractional substitution requires a cipher alphabet of the “multifid” type; that is, one in which the symbols are composed of two or more units, as in the Bacon and Trithemius al...

When the type of encipherment is unknown, the decryptor’s first problem may concern the probable language used in the plaintext, and this he is usually able to determine from th...