# Frequency analysis of transposition ciphers

Can we do frequency analysis of transposition ciphers?
If yes, please tell me the procedure and I would be happy if you provide me with some links related to it.
I heard that it can be done using bi-gram frequency.
I did it for substitution ciphers but am unable to do it for transposition ciphers.

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I did it for substitution ciphers but am unable to do it for transposition ciphers.

When it comes to transposition ciphers, it’s not really surprising frequency analysis doesn’t turn out to be as useful as it is when looking at substitution ciphers.

See, one important strength of transposition ciphers is that they are not susceptible to frequency analysis, since transposition ciphers do not change the symbols for each letter.

Instead of replacing characters with other characters, transposition ciphers just change the order of the characters. Typically, the text to be encrypted is arranged in a number of columns. These columns are then reordered, resulting in encrypted text. This means that, to decrypt/break a ciphertext created using a transposition cipher, you need to find the number of columns (which is usually based on a common factor of the total number of characters in the text) and then rearrange the columns accordingly.

Now, don’t get me wrong – frequency distribution is interesting to look at during a transposition cipher analysis, but for other reasons… frequency analysis on a transposition cipher shows that the constituent letters are what would be expected in a standard text (example: “e” is the most common English letter).

As you’re obviously just starting out to learn how to analyze and potentially decrypt/break transposition ciphers, you could check stuff like “Analysis of columnar transposition ciphers” (page 2) of “Introduction to Cryptology & Cryptosystems” by Prof. H. Williams, which provides a first, rather simple insight. Also (in contrast to Wikipedia’s related article), there are ample pages online which provide nice examples of the cryptanalysis and deciphering… randomly picking one of them: “Transposition Cipher : nrich.maths.org”.

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