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Programming Praxis: Chaocipher
In 1918, John Byrne invented a two-disk cryptographic machine, which he called a chaocipher; he drew up blueprints, but was unsuccessful in his efforts to sell the machine to the US Signal Corps and Navy. He left several challenge messages in his 1954 autobiography, but no one successfully deciphered the messages. Recently, following the death of Byrne’s son, the son’s widow donated Byrne’s complete archives, including a mock-up of the machine, to the National Cryptologic Museum at Fort Meade, Maryland. Last Friday, Moshe Rubin published the first public description of the chaocipher algorithm.
The algorithm uses two key sequences, one for cipher-text and one for plain-text. Encryption and decryption look up the desired character on one sequence and report the corresponding character on the other sequence, working from plain-text to cipher-text for encryption and from cipher-text to plain-text for decryption.
After each character, both sequences are permuted, each by a different method. Thus, the chaocipher is similar to an autokey cipher, because the key is modified according to the plain-text.
The left disk, which normally represents the cipher-text, is permuted in two steps. First, the entire alphabet is shifted left as far as cipher-text of the current character (so the current cipher-text character becomes the first character in the sequence), with the shifted-off portion of the sequence reattached at the end. Second, the second through fourteenth characters are shifted left one character, and cycled; the third character becomes the second, the fourth character becomes the third, and so on, until the fourteenth character becomes the thirteenth and the second character becomes the fourteenth. For instance, given the sequence HXUCZVAMDSLKPEFJRIGTWOBNYQ and the current character P, the entire sequence is shifted to bring P to the front, giving PEFJRIGTWOBNYQHXUCZVAMDSLK, then the second through fourteenth characters are shifted to move E after Q, giving PFJRIGTWOBNYQEHXUCZVAMDSLK. Byrne invented the terms zenith and nadir to represent the first and fourteenth characters, Rubin refers to zenith and zenith+13, but we’ll just call them by their ordinal positions in the sequence.
The right disk, which normally represents the plain-text, is permuted in three steps. First, the entire alphabet is shifted left as far as the plain-text of the current character (so the current plain-text character becomes the first character in the sequence), with the shifted-off portion of the sequence reattached at the end. Second, the first character is shifted to the end (so the current plain-text character becomes the last character in the sequence). Third, the third through fourteenth characters are shifted left one character, and cycled, similar to the left disk except for the different starting position. For instance, given the sequence PTLNBQDEOYSFAVZKGJRIHWXUMC and the current character A, the final sequence is VZGJRIHWXUMCPKTLNBQDEOYSFA.
Thus, the encryption of WELLDONEISBETTERTHANWELLSAID, given the above cipher-text and plain-text sequences, is OAHQHCNYNXTSZJRRHJBYHQKSOUJY.
Your task is to write functions that perform encryption and decryption according to the algorithm given above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
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Russian Spies ???? This is Hilarious !!!!! Does anyone BELIEVE it ? after 911 Inside JOB and ANTHRAX
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and release on the internet
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Hey YANK Bustards , NO ONE trust you. You have DESTROYED your OWN
TAGBODY in Scheme
Scheme. Not that I can imagine any real use for this, but I thought
it might be fun to try (it was). So I hacked up some code that works
surprisingly well, but I wonder if there is a more efficient and/or
obvious way to do this.
Here is what I came up with. (Nested TAGBODYs do not work properly
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Re: A link to a collection of tutorials on LISP.
That guys intention is not to spread tutorial, but its a commercial. I
clarified its true nature.
On the genocide, the thing that drives it is the lies and deception -
of people like the FBI bustards - as well as the events that took
place on the Turkish FLOTILLA.
Programming Praxis: Contents: Chronological Listing Of Exercises
You may have noticed that the Contents page changed recently. Previously the Contents page listed all the exercises in chronological order. Now, there are four listings of the exercises, in chronological order, reverse chronological order, permuted by the words in the title and summary, and organized manually by themes.
The four listings all derive from a single source. The file praxis.info consists of records separated by blank lines, fields on a single line with field name followed by a tab character followed by the data element. Here is an excerpt, which shows the header at the beginning of the file followed by the first two records:
praxis.info
number exercise number
file base name of files
pubmon month of publication
pubday day of publication
pubyear year of publication
title formatted title
ptitle plain title
blurb formatted blurb
pblurb plain blurb
exer exercise sub-page number
soln solution sub-page number
extra extra info sub-page number
codepad eight-character codepad index
theme category in which exercise appears
name/value pairs on a line separated by tabs,
with records separated by blank lines
the "number" field must appear first, others
may be in any order, and are optional
----+----1----+----2----+----3----+----4----+----5----+----6
number 1
file rpn-calculator
pubmon 2
pubday 19
pubyear 2009
title RPN Calculator
blurb Evaluate numeric expressions at the command line
exer 1
soln 2
codepad fjzlC50x
theme Parsing
number 2
file sieve-of-eratosthenes
pubmon 2
pubday 19
pubyear 2009
title Sieve of Eratosthenes
blurb A Scheme implementation of an ancient algorithm
exer 1
soln 2
codepad wI14BJ8Q
theme Prime Numbers
Four programs manipulate the data from the praxis.info file to produce the four listings. The output has elements of html, but WordPress adds the surrounding context; here is the corresponding excerpt from the listing in chronological order:
<table cellpadding="10">
<tr><td>1</td><td>19 Feb 2009</td><td><a href="/2009/02/19/rpn-calculator/">RPN Calculator</a>: Evaluate numeric expressions at the command line</td><td><a href="/2009/02/19/rpn-calculator/">exercise</a> <a href="/2009/02/19/rpn-calculator/2/">solution</a> <a href="http://programmingpraxis.codepad.org/fjzlC50x">codepad</a></td></tr>
<tr><td>2</td><td>19 Feb 2009</td><td><a href="/2009/02/19/sieve-of-eratosthenes/">Sieve of Eratosthenes</a>: A Scheme implementation of an ancient algorithm</td><td><a href="/2009/02/19/sieve-of-eratosthenes/">exercise</a> <a href="/2009/02/19/sieve-of-eratosthenes/2/">solution</a> <a href="http://programmingpraxis.codepad.org/wI14BJ8Q">codepad</a></td></tr>
</table>
Your task is to write programs that read praxis.info and write the two listing files for exercises in chronological order and reverse chronological order. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
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Re: FlateDecode, ASCIIHexDecode, ASCII85Decode, and LZWDecode streams
wrote:
I did not get enough ideas so I am expanding my posting from
gnu.emacs.help, gnu.emacs.sources, gnu.emacs.gnus, comp.text.pdf
to
gnu.emacs.help,comp.lang.lisp, comp.compression,comp.lang.sch eme,comp.text.pdf
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A vi-style editor for Scheme
certainly not too useful as a general-purpose text editor, it has
some features that facilitate editing Scheme code, like
- an interaction buffer for evaluating expressions
- a help buffer for looking up keywords and procedures
- a built-in pretty-printer
Leslie Lamport is a Jew - His book is NOTORIOUSLY uninsightful and obfuscatory
uninsightful&obfuscatory (nothing on the design of LaTeX and macros,
no insights)
but he made millions from his book as you can tell from the number of
copies sold, ie even if he got a dollar from a copy, he made millions.
Stephen Wolfram is also a jew. I wonder how his Univ of Phd studies
Jew JUDGE shows off JEW POWER by BULLYING and BLACKMAILING a BLACK PRESIDENT OBAMA
LARRY S I L V E R S T E I N - The main player in 911
Jews are coming out from the directions of Corporations, Mafias,
Legislators, and now Judge to SUBVERT the UNITED STATES.
Please listen to the Speech of Mr Benjamin H Freedman on [link]
