# enigma / doc / context / third / enigma / enigma_manual.tex

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The simulation accepts arbitrary configurations of these components, as well as the starting position of the rotors, and then processes text accordingly. Depending on the input, this yields the plaintext or ciphertext, as encryption and decryption are the same. The code is provided as a module (interface for \CONTEXT) as well as a package (\PLAIN, \LATEX). It is subject to the {\sc bsd} license, see below, \at{page}[license], for details. \stopdocchapter \startdocchapter[title=Usage] \startdocsection[title=Loading the Module / Package] The intention is for the \modulename{Enigma} codebase to integrate with the three most popular (as of 2012) \TEX\ formats: \CONTEXT, \PLAIN, and \LATEX. If the user interface does not fully conform with the common practice of the latter two, please be lenient toward the author whose intuitions are for the most part informed by \CONTEXT. For this reason, a couple words concerning the interfaces will be necessary. The examples in this manual will be cycling through all three formats, but once you get the general idea of how it works, you will have no problem translating between coding styles. Those familiar with \CONTEXT\ might, therefore, skip the following paragraphs and continue directly with the next section on \at{page}[sec:opts].% The package is loaded as usual. For \PLAIN, issue a \type{\input{enigma}}. \LATEX-users need to place \type{\usepackage{enigma}} somewhere inside the preamble. (There are no package options.) From this point on, instructions for both formats are the same. The interface provides two basic macros from which all functionality will be derived: \texmacro{defineenigma} and \texmacro{setupenigma}. Both are a kind of \emph{meta-macros}, meaning that they generate other macros which may then be employed to access the functionality of the package. As such they naturally belong inside the preamble (if you chose to use \modulename{Enigma} with \LATEX, that is). It follows that the correct and only meaningful order is to \texmacro{defineenigma} an enigma machine first and then \texmacro{setupenigma} it. The former takes a single, the latter a double argument. Thus, \type{\defineenigma{encrypt}} creates a new environment consisting of the macros \texmacro{startencrypt} and \texmacro{stopencrypt}.% \footnote{% \CONTEXT-users will have noticed that there is no simple macro \type{\encrypt{foo}}. The reason for this is that the callback which the module relies on operates on node-level. This means that for the Enigma encryption to have an effect it will have to process entire paragraphs. As encrypted passages are supposed to stand on their own, this small limitation should not have a severe impact on functionality. If you should, however, need a macro that works for smaller portions of text, please send a feature request to the maintainer (\ichdparameter{email}). } However, these are not usable right away, as we still have to set the initial state of the machine. This is achieved by the second meta-macro, \type{\setupenigma{encrypt}{}}, where \type{} is a placeholder for a list of \emph{assignments}, i.\,e. pairs of \emph{key=value} statements by means of which all further parameters are specified. The possible parameters are listed in the next section, examples of their effects will be given further below in the section on functionality (see \at{page}[sec:fun]).% \footnote{% If you grasp the concept of paired \type{\define} \endash\space \type{\setup} macros, then congratulations are in order: you qualify for migration from your current macro package to \CONTEXT. } \stopdocsection \startdocsection[title=Options Explained,reference=sec:opts] At the moment, the \texmacro{setupenigma} macro in any format accepts the following parameters. % \startpostponing[+2]%% messes up floats -- why? \placefigure[right]{Usage example for the \PLAIN\ format.}{ % \framed[align=right,frameoffset=1em]{% \framed[align=right,frameoffset=1em,frame=off]{% \startlatextyping[before=,after=,] \input {enigma} %% Definition ··········· %% \defineenigma {encryption} %% Setup ················ %% \setupenigma {encryption} { other_chars = no, day_key = I II III 01 01 01, rotor_setting = aaa, spacing = yes, verbose = 1, } %% Usage ················ %% \startencryption aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa \stopencryption \startencryption Nobody in Poland is going to be able to read this, har har! \stopencryption \bye \stoplatextyping } } % \stoppostponing \startitemize \setuptolerance[tolerant]%% it’s crowded in here due to the float \let\olditem\item \let\item\undefined \def\item#1#2{% 1 name, 2 type \olditem \identifier{#1}% \reference[option:#1]{}% \space <\emph{#2}>% \hskip1em% } \item{other_chars}{boolean} How to handle non-encodable characters, i.\,e. glyphs outside the bare set of Latin letters; see below on \at{page}[explained:other_chars]. \item{day_key}{string} Encryption key, i.\,e. a description of the initial setup of an Enigma machine: the reflector used, the choice and positions of the three rotors, the ring settings, and the plugboard wiring. \item{rotor_setting}{string} The initial rotor advancement. \item{spacing}{boolean} Auto-space output? \item{verbose}{integer} Controls overall verbosity level (\emph{global}\/!). \stopitemize %% day key To state the obvious, the value of \identifier{day_key} serves as the \emph{day key} for encryption. An Enigma day key ordinarily consists of (1) a list of the the rotor configuration, (2) the ring settings, and (3) the plugboard connections.\footnote{% For a description of the initialization process see \from[initialization]. } Together these have the denotation \emph{day key}, because they are meant to be supplied in special code books by central authority, one for each day.\footnote{% Read about the historical directives for daily key renewal at \from[key_procedure]. there are some {\sc pdf}s with images of \emph{Kenngruppenbücher} at \from[ecollection], section \emph{Enigma Messages and Keys}. Also, while you’re at it, don’t miss the explanation on Wikipedia: \from[wp:day_key]. } In the \modulename{Enigma} setup, the day key starts with a triple of Roman numerals ({\sc i} to {\sc v}) describing which of the five rotors is located in which of the three slots. (e.\,g. \type{I VI II}).\footnote{% For the individual wirings of the five rotors see \from[rotor_wirings], as well as the implementation below at \at{page}[listing:rotor_wiring]. } Its next part is the ring setting, a triple of two-digit integers that are the amount by which the internal wiring of each rotor has been shifted (\type{03 23 11}). As the Enigma encrypts only the letters of the Latin alphabet, sane values range from one (first position: no shift) to twenty six.\footnote{% Consult \from[wp:ring] for an introduction into the ring mechanics. } The third section specifies which pairs of letters are substituted by each other by means of plugboard connections (\type{NI CE GO LD ...}). There can be zero to thirteen of these redirections, thus the presence of this section is entirely optional. Also part of the \identifier{day_key}, but not mentioned yet, is the choice of the \emph{reflector}. It may be specified as one of the three letters \type{A}, \type{B} and \type{C} as the first item. If no reflector is requested explicitly, the machine defaults to \type{B}, which is actually the only one of the three models that had been in widespread use (see below on \at{page}[listing:reflector] for the wirings). Initialization is not complete without a \identifier{rotor_setting}. This is a triple of letters, each representing the initial state of one rotor (e.\,g. \type{fkd}). Historically this was not part of the day key but supposed to be chosen at random by the operating signal officer. The output can be automatically grouped into sequences of five characters, delimited by spaces. This does not only conform with traditional crypto-style, but also allows for the resulting text to be sanely broken into lines by \TEX. %%% other_chars % The option \identifier{other_chars} determines how the machine -- in % our Unicode-aware times -- should behave when it encounters a % non-Latin letter. For the time being it can either remove them from % the input (value \emph{no}) or pass them through unmodified % (\emph{yes}). Note that this is independent of the % \emph{preprocessing} of characters like punctuation and umlauts, % which is done automatically. % (See below \at{page}[listing:preproc] for the internal substitution % list.) Most documents don’t naturally adhere to the machine-imposed restriction to the 26 letters of the Latin alphabet. The original encipherment directives comprised substitution tables to compensate for a set of intrinsic peculiarities of the German language, like umlauts and common digraphs. The \modulename{Enigma} simulation module strives to apply these automatically but there is no guarantee of completeness. However,\reference[explained:other_chars]{} the Enigma lacks means of handling languages other than German. When the substitution lookup fails, there are two ways of proceeding: either to ignore the current character or to pass it on to the output as if nothing happened. The default behaviour is to drop alien letters and move on. If the user intends to keep these foreign characters instead, E can achieve this by setting the \identifier{other_chars} key in the \modulename{Enigma} setup to the value \emph{true}. An example of how the result of both methods may look, other things being equal, is given in below listing (example for \CONTEXT; see the file \type{enigma-example-context.tex} in the \type{doc/} subtree of your installation path). \startcontexttyping \usemodule [enigma] \defineenigma [secretmessage] \setupenigma [secretmessage] [ other_chars = yes, day_key = B V III II 12 03 01 GI JV KZ WM PU QY AD CN ET FL, rotor_setting = ben, ] \defineenigma [othermessage] [secretmessage] \setupenigma [othermessage] [other_chars=wrong] \starttext \startsecretmessage føo bąr baž \stopsecretmessage \startothermessage føo bąr baž \stopothermessage \stoptext \stopcontexttyping Both methods have their disadvantages: if the user chooses to have the unknown characters removed it might distort the decrypted text to becoming illegible. Far more serious, however, are the consequences of keeping them. As artefacts in the ciphertext they would convey information about the structure of the plain text. \stopdocsection \startdocsection[title=Basic Functionality,reference=sec:fun] Encrypt the text of your document using the script interface. For a start try out the settings as given in below listing. \starttyping mtxrun --script mtx-t-enigma \ --setup="day_key = B I II III 01 01 01, \ rotor_setting = xyz, \ verbose=0" \ --text="Gentlemen don’t read each other’s mail, Mr. Turing\!" \stoptyping This will result in the thoroughly scrambled string \typ{omribshpwfrfjovkntgqgi abbkhjpxmhdztapkatwrvf}. Then, use the same settings you encrypted the text with in your document. \startcontexttyping \usemodule[enigma] \defineenigma [secretmessage] \setupenigma [secretmessage] [ day_key = B I II III 01 01 01, rotor_setting = xyz, verbose=3, ] \starttext \startsecretmessage omribshpwfrfjovkntgqgiabbkhjpxmhdztapkatwrvf \stopsecretmessage \stoptext \stopcontexttyping If you compile this document with \CONTEXT, the plain text will reappear. Notice that punctuation is substituted with the letter “x” before encryption and that spaces are omitted. \useURL[kgbuch] [http://de.wikipedia.org/wiki/Kenngruppenbuch] [] [code book] Now it’s certainly not wise to carry around the key to encrypted documents as plain text within those documents. The keys will have to be distributed via an independent channel, e.\,g. a \from[kgbuch]. Keys in general don’t have to be supplied inside the document. If there is none specified, the module will interrupt the \TEX\ run and \emph{ask} for user input. Suppose Alice wanted to send an encrypted file to Bob and already generated the cipher text as follows: \starttyping mtxrun --script mtx-t-enigma \ --setup="day_key =B I IV V 22 07 10 AZ DG IE YJ QM CW, \ rotor_setting = bar, \ verbose=0" \ --text="I have nothing to hide. From the NSA, that is." \stoptyping Alice would then include the result of this line in her \LATEX\ document as follows: \startlatextyping \documentclass{scrartcl} \usepackage{enigma} \defineenigma{decryption} %% Encryption key not given in the setup. \setupenigma{decryption}{ rotor_setting = bar, verbose = 3, } \begin{document} \startdecryption usbatbwcaajhzgeyzkqskupzbmdhbdepccgeh \stopdecryption \end{document} \stoplatextyping She subsequently mails this file to Bob and conveys the key through a secure channel. They only thing that will be left for Bob to do now, is to enter the key at the prompt when compiling the document with \LUALATEX. \stopdocsection \startdocsection[title=Uses and Abuses] In \LUATEX, \identifier{callback}s may stack. This allows filtering the input through many enigma machines successively. For instance, in the following listing, two instances of the same machine are generated and applied. \startcontexttyping \usemodule [enigma] %% load the module \defineenigma [secretmessage] %% generate and \setupenigma [secretmessage] [ %% configure a machine day_key = B IV V II 01 01 01 AD CN ET FL GI JV KZ PU QY WX, rotor_setting = foo, verbose=3, ] %% now, copy the first machine’s settings \defineenigma [othermessage] [secretmessage] %% here we go! \starttext \startothermessage %% enable machine 1 \startsecretmessage %% enable machine 2 while no 1 is active Encryption equals decryption. \stopothermessage \stopsecretmessage \stoptext \endinput \stopcontexttyping \stopdocsection \stopdocchapter \startdocchapter[title=Metadata] \startdocsection[title=License,reference=license] © 2012 \emph{Philipp Gesang}. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: \startitemize[n] \item Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. \item Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. \stopitemize \begingroup \setuptolerance [horizontal,strict] \startalignment [right,nothyphenated] \noindentation\startsmallcaps this software is provided by the copyright holder “as is” and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. in no event shall the copyright holder or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage. \stopsmallcaps\endgraf \stopalignment \endgroup \stopdocsection \startdocsection[title=Acknowledgements] \startcredits \item The idea to implement the \emph{Enigma} cipher for \TEX\ came up while I was reading \emph{The Code Book} by Simon Singh. This work contains an excellent portrayal of the history of German military cryptography and Allied cryptanalysis before and during the Second World War.\par \from[codebook] \item A more detailed account from a historical-cryptological perspective is provided by Ulrich Heinz in his Dissertation (in German), which is freely available. Includes an interesting albeit speculative note on the effectiveness of the Soviet code breaking efforts (chapter seven).\par \from[heinz_diss] \item Also, the \modulename{Enigma} module drew lots of inspiration from Arno Trautmann’s \modulename{Chickenize} package, which remains the unsurpassed hands-on introduction to callback trickery.\par \from[chickenize] \item Finally, without \LUATEX, encryption on node-level would not have been possible.\par \from[luatex-web] \stopcredits \stopdocsection \stopdocchapter 
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