How Row Transposition Encryption Algorithm Work

How Row Transposition works?
Transposition Ciphers

• transposition or permutation ciphers hide the message contents by rearranging the order of the letters

Scytale cipher

• an early Greek transposition cipher
  
• a strip of paper was wound round a staff
  
• message written along staff in rows, then paper removed
  
• leaving a strip of seemingly random letters

Reverse cipher

write the message backwards

Code:

Plain:   I CAME I SAW I CONQUERED
Cipher:   DEREU QNOCI WASIE MACI

Rail Fence cipher

• write message with letters on alternate rows
  
• read off cipher row by row

Code:

Plain:   I A E S W C N U R D
         C M I A I O Q E E
Cipher:   IAESW CNURD CMIAI OQEE

Row Transposition ciphers

• In general write message in a number of columns and then use some rule to read off from these columns
  
• key could be a series of number being the order to: read off the cipher; or write in the plain-text

Code:

Plain:   THESIMPLESTPOSSIBLETRANSPOSITIONSXX
Key (R):      2 5 4 1 3   
Key (W):                           4 1 5 3 2    

              T H E S I      S T I E H    
              M P L E S      E M S L P    
              T P O S S      S T S O P    
              I B L E T      E I T L B    
              R A N S P      S R P N A    
              O S I T I      T O I I S    
              O N S X X      X O X S N
Cipher:   STIEH EMSLP STSOP EITLB SRPNA TOIIS XOXSN

or can use a word, with letter order giving sequence: to write in the plain-text; or read off the cipher

Code:

Plain:   ACONVENIENTWAYTOEXPRESSTHEPERMUTATION
Key (W):      C O M P U T E R
Key (W):      1 4 3 5 8 7 2 6
   
              A N O V I N C E
              E W T A O T N Y
              H E P R T U E M
              A O I N Z Z T Z

Cipher:       ANOVI NCEEW TAOTN YHEPR TUEMA OINZZ TZ


key idea for row transposition ciphers is that message is in groups that have the letters reordered in each
Exercise using key sorcery (to read out) encipher:

Code:

Key(R):   sorcery => 6 3 4 1 2 5 7

laser beams can be modulated to carry more intelligence than radio waves

gives:

Code:

erasb lecam snabd umole atoed ctamo ryrre elntl iicee ntgha dnria oesav w

Decryption consists of:

• writing the message out in columns
  
• reading off the message by reordering columns
  
• (use T command in krypto, uses read out keys)

hint - its not a good idea to leave message in groups matching the size of your key!

Cryptanalysis of row transposition ciphers

A frequency count will show a normal language profile hence know have letters rearranged basic idea is to guess period, then look at all possible permutations in period, and search for common patterns (eg t command in krypto)

• use lists of common pairs & triples & other features

To determine the complexity of this cipher, we can calculate its unicity distance
Given blocks of period d, there are d! keys, hence

Code:

N = F(H(K),D) = F(log_(2)d!,D) = F(d log_(2)(d/e),3.2)

Block (Columnar) Transposition ciphers
Another group of ciphers are block (columnar) transposition ciphers where the message is written in rows, but read off by columns in order given by key (use B command in krypto) for ease of recovery may insist matrix is filled :

Code:

Key(R):       s o r c e r y        s o r c e r y
Key(R):       6 3 4 1 2 5 7        6 3 4 1 2 5 7

              l a s e r b e        l a s e r b e
              a m s c a n b        a m s c a n b
              e m o d u l a        e m o d u l a
              t e d t o c a        t e d t o c a
              r r y m o r e        r r y m o r e
              i n t e l l i        i n t e l l i
              g e n c e t h        g e n c e t h
              a n r a d i o        a n r a d i o
              w a v e s            w a v e s q r



Giving ciphertext (by reading off cols 4, 5, 2, 3, 6, 1, 7)

Code:

ecdtm ecaer auool edsam merne nasso dytnr vbnlc rltiq laetr igawe baaei hor

Decryption consists of:

• calculating how many rows there are (by dividing message length by key length)
  
• then write out message down columns in order given by key

Find code for Row Transposition Here ( Java and C#)
Moved to :
http://www.codemiles.com/finished-projects/row-transposition-cipher-encryption-decryption-java-t10766.html
http://www.codemiles.com/c/row-transposition-cipher-encryption-decryption-csharp-c-t658.html

For information on lots of simple substitution and permutation ciphers see:

A. Sinkov "Elementary Cryptanalysis", New Mathematical Library, Random House, 1968* other simple transposition ciphers include:

Attachments

Transpositions.rar

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