Route Transposition Cipher

A cipher which retains all of the letters of the plaintext message but simply changes their order is referred to as transposition cipher, unlike a substitution cipher which substitutes one letter for another. There are many ways to rearrange the letters of a word or message. A simple reverse order of the word” transposition” in ciphertext becomes NOITISOPSNART. Cryptology’s battle of wits between the cryptographer and the cryptanalyst through the years discarded this encipherment as too easy to decipher, leading to encipherment processes of a more complex nature. The Route Transposition cipher type is one of those systems.

The Route Transposition Cipher (Construction)

One form of a transposition cipher is where plaintext is converted to ciphertext by constructing it in a specific arrangement of rows, columns, spirals or diagonal paths and extracting it by, yet, another predetermined path sequence. The letters must form a complete square or rectangle. A picture is worth a thousand words:

W A R L F
H S W S L
A F H A I
T O E N E
H U E D S

Extraction of the letters by rows in the above matrix produces a ciphertext of WARLF HSWSL AFHAI TOENE HUEDS, but a vertical read of its columns reveals a plaintext message of “What has four wheels and flies?” Let’s try another:

T R U C K
E O V E W
G C X R I
A O N H T
B R A G A

A vertical read of these columns produces a ciphertext of TEGAB ROCOR UVXNA CERHG KWITA but a counter-clockwise spiral read of the matrix beginning in the lower right hand corner will reveal a plaintext message of “A garbage truck with no cover.”

Complexity of the Route Transposition Cipher

The ease of construction of the Route Transposition Cipher, coupled with its infinite number of paths or routes of placing the plaintext in and extracting it out makes this a highly desirable form of encipherment.

Both messages above could have been enciphered in any number of paths, horizontal rows or vertical columns, consecutive or alternating paths, reverse order paths, diagonal routes, spiral routes, while making use of any number of starting points.

Solving the Route Transposition Cipher

Let’s begin with an easy ciphertext construction whose title line indicates the number of letters in the construction.

RT-1.   Abe Lincoln at Gettysburg (25)          LIONEL

FCNER  OODNS  URSYA  REEEG  SAVAO
  1. Determine the number of columns needed to form a complete square or rectangle.
  2. Post the ciphertext by column or row.
  3. Look for readable plaintext.

Route Transposition Possible Paths

Our completed square or rectangular matrices may use any of the following routes or combination of routes to insert plaintext and extract ciphertext:

  • Horizontal     – Alternating Horizontal
  • Vertical         – Alternating Vertical
  • Diagonal       – Alternating Diagonal
  • Clockwise Inward or Outward Spiral
  • Counterclockwise Inward or Outward Spiral
  • Starting Positions – Upper, lower left and right

These represent the common routes that you will find in our Cm cipher constructions, but do by no means represent all of the possible routes that may be available for encipherment in the real world of secret messaging. Routing can include geometric designs, pictorial artistry and ad infinitum schemes limited only to the boundaries of the creative mind. The seemingly limitless route choices and ease of cipher construction makes this a highly desirable cipher type for secret messaging.

Construction

We’ll use a twenty-five block matrix to review many of the available routes for the encipherment of the plaintext “A Route Transposition Cipher,”

A R O U T
E T R A N
S P O S I
T I O N C
I P H E R

The plaintext is entered in horizontal rows, but it need not be. Check out the variations in the ciphertext when the letters are extracted from various routes:

Rows    
  Alternating
AROUT NARTE SPOSI CNOIT IPHER
  Reversed
TUORA NARTE ISOPS CNOIT REHPI
Columns  
AESTI RTPIPOROOH UASNE TNICR
  Alternating
AESTI PIPTR OROOH ENSAU TNICR
  Reversed
ITSEA PIPTR HOORO ENSAU RCINT
Spiral    
  Clockwise
AROUT NICRE HPITS ETRAS NOIPO
  Counter Clockwise
OPION SARTE STIPH ERCIN TUORA
Diagonal  
AERST OTPRU IIOAT POSNH NIECR
  Alternating
AREST OURPT IIOAT NSOPH NICER
  Reversed
AREOT SURPT TAOII NSOPI NHCER

When we note that all of these extracted ciphertext variations begin at the upper right or left corners of the grid, you can appreciate the complexity of the Route Transposition with encipherment beginning options still available at other locations of the grid. Increasing the complexity of this cipher type, is the option of installing the plaintext in these same route variations, which prompts the question,” What is an innocent solver to do?” Getting started:

RT-2.  Heredity.    (56)    (from)            LIONEL

Look for the rest of the crib adjacent to the only “F” in the matrix.

L I H C T S O M
C S E D N E R D
O R F D E D N E
I L G N O L A M
M R I E H T E N
I L S R E H T O
O T D E N E T S

RT-3. Optical Illusion  (70)    (two)        LIONEL

X E E S R A Y
F L D E E I L
L C A S T C N
E A M S H I O
S T E A G T S
R C H L U P A
E E S G A O W
H P D O D E E
F S N W S H H
O A A T N T S

Now it’s on to the need for some cryptanalyst procedures for the remaining ciphers.

Route Transposition Solution Procedures

  1. Determine the grid size by the number of letters.
  2. Assume as near a square as possible (ACA Guidelines call for 8 x 8 square maximum and 8 x 10 rectangle maximum.
  3. Look for word portions in normal alphabetical order. (See row and spiral example above.)
  4. Where cribs are provided, look for grid adjacent letter sequences which support the crib.
  5. Reconstruction relies heavily on trial and error.
  6. The letter “X” is often used as a null letter to satisfy the number of positions needed in a Route Transposition and can be a signal to its ending.

RT-4. Just Desserts.   (45)  (job)                LIONEL

TFLDI  HOLHT   ERDAS  RAOVO  EJNEW  WOEOE  ABIOL  RWSNL  DETEX..

RT-5.  Geometric Detour     (56)    (between)      LIONEL

TOTAE  NOIES  THRDN  TTISR  RTIET  ICWWN  UCROS  ESEEO  TNOUN  HSTBE
PSDNC  X.

RT-6.  Vision.   (84)   (usual)       LIONEL

TRSWH  UEIDF  NSHVO  IASTS  UOCTE  OCLVU  IMERI  ACYIL  EANOT  ERNLA  ENILG  NOSCC  ANTOT  MTTUE  UEITY  TSEHH NEMS.