No Subject

[one4evil@juno.com (Nalus Optic)]

Ok, I was just going through Phrack 51again and found this...I don't know
if you people care or are seeing it for the 51 time, but if you want the
whole thing, e-mail me or just go do a search for Phrack and look at
there archives...There is a lot more to the artical, but this little bit
lets you know what it is about.
		
			D.



---[  Phrack Magazine   Volume 7, Issue 51 September 01, 1997, article 13
of 17


-------------------------[  Monoalphabetic Cryptanalysis (Cyphers, Part
One)


--------[  Jeff Thompson aka 'Mythrandir' <jwthomp@cu-online.com>



Written for Phrack and completed on Sunday, August 31st, 1997.


---------

First a quick hello to all of those I met at DefCon this year.  It was 
incredible fun to finally put faces to many of the people I have been
talking 
with for some time.  It was truly was a treat to meet so many others who
are 
alive with the spirit of discovery.  

----------


This is the first in a series of articles on Cryptology that I am
writing.  
The goals of these articles will be to attempt to convey some of the
excitement
and fun of cyphers.  A topic of much discussion in regards to
cryptography 
currently, is about computer based cyphers such as DES, RSA, and the PGP 
implementation.  I will not be discussing these.  Rather, these articles
will 
cover what I will term classical cryptology.  Or cryptology as it existed

before fast number crunching machines came into existance.  These are the
sorts
of cyphers which interested cryptographers throughout time and continue
to be 
found even to this very day.  Even today, companies are producing
software 
whose encryption methods are attackable.  You will find these commonly
among 
password protection schemes for software programs.  Through the course of
these
articles I will explain in practical terms several common cypher types
and 
various implementations of them as well as cryptanalytic techniques for 
breaking these cyphers.

Creating cyphers is fun and all, but the real excitement and often times
tedium
is found in Cryptanalysis.  Many of the ideas presented in these articles
will 
based on three sources.  The following two books: The Codebreakers by
David 
Kahn (ISBN: 0-684-83130-9) and Decrypted Secrets by F.L. Bauer 
(ISBN: 3-540-60418-9).  Both authors have put together wonderful books
which 
both cover the history and methods of Cryptology.  Do yourself and the
authors 
a favor and purchase these books.  You will be very pleased with the lot.
 
Finally, a miniscule amount of these articles will be written based on my
own 
personal experience.  

The fun is in the journey and I welcome you on what is certain to be an 
interesting trip.  Please feel free to raise questions, engage me in 
discussions, correct me, or simply offer suggestions at
jwthomp@cu-online.com.
Please be patient with me as I am traveling extensively currently, and
may be 
away from the computer at length occasionally.  

Out the door and into the wild...


--Monoalphabetic Cyphers

Monoalphabetic cyphers are often currently found in simple cryptograms in
books
and magazines.  These are just simple substitution cyphers.  This does
not 
mean that they are always simple for the beginning amateur to solve.

Three common monoalphabetic cyphers which are used are substitution,
cyclical, 
and keyed cyphers.


-Substitution Cyphers 

By taking an alphabet and replacing each letter with another letter in a 
unique fashion you create a simple monoalphabetic cypher.  

Plaintext Alphabet	A B C D E F G H I J K L M N O P Q R S T U V W X
Y Z
Cypher Alphabet		Z I K M O Q S U W Y A C E B D F H J L N P
R T V X G


Plaintext Message

The blue cow will rise during the second moon from the west field.

Cyphertext Message

nuo icpo kdt twcc jwlo mpjwbs nuo lokdbm eddb qjde nuo toln qwocm.


-Cyclical Cyphers

By taking an alphabet and aligning it with a rotated alphabet you get a 
cyclical cypher.  For example:

Plaintext Alphabet	A B C D E F G H I J K L M N O P Q R S T U V W X
Y Z
Cypher Alphabet		N O P Q R S T U V W X Y Z A B C D E F G H
I J K L M


Indeed, you may recognize this cypher as a ROT13 which is commonly used
on 
news groups to obscure messages.


-Keyed Cypher

Another way to create a monoalphabetic cypher is to choose a keyword or
phrase 
as the beginning of the cypher alphabet. Usually, only the unique letters
from 
the phrase are used in order to make sure the plaintext to cyphertext
behaves 
in a one to one fashion.

For example:

Plaintext Alphabet:	A B C D E F G H I J K L M N O P Q R S T U V W
X Y Z
Cypher Alphabet		L E T O S H D G F W A R B C I J K M N P Q
U V X Y Z

The passphrase in this cypher is "Let loose the dogs of war"  The
advantage of 
such a system is that the encryption method is easy to remember.  Also, a

method of key change can be created without ever having to distribute the
keys.
For example, one could use the 4 words at a time of some piece of
literature.  
Every message could use the next four words.  Indeed, this change could
occur 
more frequently, but that is a subject for another article. 



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