Simple Ciphers - Modern Cryptanalysis: Techniques for Advanced Code Breaking - page 4

swordfihabcegjklmnpqtuvxyz
Note that the second s was removed from the keyword in the alphabet and that the alphabet is still 26 char-
acters in length.
Thereareafewdisadvantagestousingsuchatechnique.Forexample,encryptingamessagethatcontainsthe
keyword itself will encrypt the keyword as a string of letters starting something along the lines of ABCDEFGH .
Another, probably more severe disadvantage is that letters near the end of the alphabet will not be shifted at all
unless the keyword has one or more characters appearing at the end of the alphabet, and even so, would then
likely be shifted very little. This provides patterns for the experienced code breaker.
1.2.2 ROT13
A modern example of a monoalphabetic cipher is ROT13, which is still used on the Internet, although not as
much as it has been historically. Essentially, this is a simple cipher in the style of the Caesar cipher with a shift
of +13.
Thebeauty ofthiscipher isinitssimplicity: Theencryption anddecryption operations areidentical. Thisfact
is simply because there are 26 letters in the Latin alphabet (at least, the way we use it in English); thus, shifting
twice by 13 yields one shift of 26, which puts things back the way they were. Also note that it doesn't matter in
which “direction” we shift, since shifting left by 13 and shifting right by 13 always yield the same results.
But why use such an easy-to-break cipher? It's, in fact, trivial to break since everyone knows the cipher al-
phabet! Despite the fact that this style of cipher has been obsolete for centuries, ROT13 is useful to protect
slightly sensitive discussions.Forexample,readers of a message board might discuss the endings of topics using
ROT13 to prevent spoiling the conclusion for others.
Looking through articles or posts on the Internet where sensitive topics might be displayed, and suddenly
having the conversation turn into strange-looking garbage text in the middle (often with other parties replying
in the exact same code) often means that the posters are writing in ROT13. Plus, ROT13 often has a very dis-
tinctive look that one can recognize after a while. For example, our standard text from above,
the quick brown roman fox jumped over the lazy ostrogoth dog
would display as
GUR DHVPX OEBJA EBZNA SBK WHZCRQ BIRE GUR YNML BFGEBTBGU QBT
when encrypted with ROT13.
1.2.3 Klingon
I would like to delve into a language other than English for a moment, to show that these cryptographic (and
later, cryptanalytic) techniques are not reliant on English, but can have similar properties in other languages as
well, including even constructed languages. An example language that might be easy to follow is the Klingon
language.
Klingon [1] (more properly, “tlhIngan Hol”), as seen in the Star Trek films and television shows, is an ar-
tificial language invented mostly by Marc Okrand using only common Latin characters and punctuation. This