Cryptanalyzing Monoalphabetic Substitution by Cribbing
======================================================

Solution by Michael Lee



Cribs to try: network, computer, protocol, layer, socket, tcpip, connection

First searched for "network."  The following isomorph has a score of 39 and 
appears eleven times:

=======
NETWORK
htzvgsl
=======

The next thing to try is almost always "the." The following isomorph has a score
of 7 and appears 16 times (just as importantly, T and E match with the results
for "network" from above):

===
THE
zit
===

"Computer" is next, and is only found once, but it matches closely with results
for "network" and has an insanely low score of 3.9.

========
COMPUTER
egjfxzts
========

To summarize, we now know:

=========  ======
ETAONRISH  WKCMPU
tz ghs  i  vlejfx
=========  ======

We can now start guessing the substitutions for individual letters because we 
can recognize words (with a letter or two missing). 

Tip: Remove all original spaces in the ciphertext and add your own as you 
discover word boundaries.  This makes guessing character substitutions easier.

=========================================
the words:       imply the substitutions:
---------------  ------------------------
NUMwER           w>B
PROCEaa PREaENT  a>S
MESSquE          q>A  u>G
MUkToPURPOSE     k>L  o>I                (now we have ETAONRISH!)
Oy               y>F
CURRENTLn        n>Y
dUESTION         d>Q
EbISTENCE        b>X
INCLUrE          r>D
RESERcATION      c>V
=========================================

To summarize, we have:

========================
ABCDEFGHIKLMNOPQRSTUVWXY
qwertyuiolkjhgfdsazxcvbn
========================

querty!??! grr

And now the plaintext, with asterisks around apparent typos:

================================================================
DATA NETWORKS OF VARIOUS KINDS ARE CURRENTLY IN EXISTENCE OR 
IN THE PROCESS OF BEING SETUP THESE INCLUDE LARGE SCALE COMPUTER
NETWORKS SUCH AS THE ARPA NETWORK THE FRENCH CYCLADES
NETWORK AND THE MULTIPURPOSE DATA NETWORKS SETUP OR PROPOSED
BY THE BRITISH POST OFFICE THE *TRANSCANDA* TELEPHONE SYSTEM
DATRAN AND ATT AMONG OTHERS AIRLINE RESERVATION SYSTEMS
MEDICAL DATA NETWORKS BANKING NETWORKS INFORMATION SERVICE
NETWORKS AND SOON THE NUMBER IS ENDLESS AND GROWING RAPIDLY
IN THIS BOOK WE PROPOSE TO PRESENT IN A QUANTITATIVE WAY WHERE
POSSIBLE ASPECTS OF NETWORK DESIGN THAT ARE BROADLY APPLICABLE
TO MOST OF THESE NETWORKS THESE INCLUDE *QUESTION* RELATED
TO THE ENTRY OF MESSAGES INTO THE NETWORKS AND THE COMBINING
OF MESSAGES FROM A MULTIPLICITY OF TERMINALS LOCATED
IN ONE CONTIGUOUS GEOGRAPHIC AREA AS WELL AS THE GLOBAL
QUESTION OF ROUTING THE MESSAGE STREAMS TO A MULTIPLICITY OF 
REMOTE LOCATIONS LENGTH
================================================================