[Abstract]
The purpose of this document is to analyze cryptographic transposition techniques by showing a few examples of some different techniques. The next portion of this document is to provide an answer to the question “Is it possible to decrypt the message that was encrypted with a two-stage transposition technique with a different key?” The last part of this document provides supporting information to the argument, “The Transposition cipher technique works by permuting the letters of the plaintext. It is not very secure, but it is great for learning about cryptography.” This document provides a basic knowledge and understanding of how different encryption techniques can be used and is intended for use by anybody interested in gaining a basic knowledge of encryption techniques.
[Content]
Three different encryption techniques are primitive in nature, however they illustrate different techniques that can be used to secure data. The three different techniques used will use the following message as an example of the data to be protected: “The Transposition cipher technique works by permuting the letters of the plaintext. It is not very secure, but it is great for learning about cryptography.” One technique that is used is called the rail fence technique. This method works by offsetting every other letter in a message and then putting the second line of text behind the first line. This method is illustrated in the following example.
Transposition Technique: Rail Fence
Plain Text: thetranspositionciphertechniqueworksbypermutingthelettersoftheplaintextitisnotverysecurebutitisgreatforlearningaboutcryptography
Cipher Text: ternpstocpetcnqeokbpruighltesfhpanettsovrscrbttsrafrerigbucytgahhtasoiinihrehiuwrsyemtnteetrotelitxiinteyeueuiigetolannaotrporpy
The next technique is called the columnar transposition. This method works by using a key and inputting the message in a number of columns that is identified by the key and then the number of characters in the message itself identifies the number of rows. After the message is placed into the rows and columns then the characters in each column is placed in the order identified by the key (Stallings, 2006). This is illustrated in the following example.
Transposition Technique: Columnar Transposition
Key: 2315746
Plain Text: thetran
spositi
onciphe
rtechn
iquewo
rksbyp
ermuti
ngthele
ttersof
thepla
intexti
tisnotv
erysecu
rebutit
isgreat
forlear
ningabo
utcrypt
ography
Cipher Text: eoceusmteetsybgrncrtsorirentiterifnuohpntqkrgthniresoitgathhwytlolttciaabphtsicebuhrpeosurlgranienopiefaiyuttrotyripcebuespxoeteeayp
The last technique is called the double transposition. This method is very similar to the columnar transposition, except that after the cipher text is determined after the initial encryption, then the cipher text in put back through the matrix and encrypted a second time. This is illustrated in the following example.
Transposition Technique: Double Transposition
Key: 2315746
Plain Text (1st Cipher Output): eoceusm
teetsyb
grncrts
orirent
iterifn
uohpntq
krgthni
resoitg
athhwyt
lolttci
aabphts
icebuhr
peosurl
granien
opiefai
yuttrot
yripceb
uespxoe
teeayp
Cipher Text (2nd Cipher Output): ceniehgshlbeoaitiseetgoiukralaipgoyyutoerrtoretoacerpureesytnftntycthreaoeoyetcrrptohtpbsnetppambstnqigtisrlnitbeusreinhiwthuuifrcxy
When the question is asked, “Is it possible to decrypt the double transposition message with a different key?” the answer is simply “yes.” The matrix transposition ciphers can be cracked because they use a fixed number of characters to develop a matrix. By simply counting the total number of letters can help to guess what size matrix is to be used. Once the total number of letters is known, then it is a matter of trying all variations of different sizes of matrices. By filling in the matrix with the characters both horizontally and vertically a person can look for patterns. By using this methodology, with a little trial and error, a person can continue to try different sized matrices and filling in the letters to look for patterns of letters to spell words (NOVA, 2000). This methodology is essentially recreating the key, but the whole key may not be needed to completely understand the message. Due to the fixed size of matrices used for the matrix transposition method, it is possible to crack the message by using a different or incomplete key.
“The Transposition cipher technique works by permuting the letters of the plaintext. It is not very secure, but it is great for learning about cryptography,” is a true statement. To better understand this statement it is important to understand what the statement is saying. The statement is saying that the transposition cipher technique works by changing the letters of plaintext. As previously illustrated in the previous examples, one can clearly see that this technique of encryption works by simply changing the order of the characters in the original plain text and therefore that is a true statement.
In conclusion, the transposition techniques of changing the order of the characters in the original plain text message are primitive means of encrypting the original message. Although the rail fence, matrix transposition, and the double transposition methods are good for learning about encryption techniques, they are not ideal for encrypting any real messages. Due to using the original plain text of the message, one is able to crack the encryption technique by using a different or incomplete key.
References
1. Stallings, William (2006). Cryptography and Network Security (Fourth Edition). Upper Saddle river, NJ: Pearson Prentice Hall. (2000, November).
2. The Double Transposition Cipher. Retrieved February 11, 2009, from >NOVA Online | Decoding Nazi Secrets | The Double Transposition Cipher Web site: http://www.pbs.org/wgbh/nova/decoding/doubtrans.html