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Breaking Letter Substitution codes

A Letter Substitution Cipher replaces the letters in the alphabet with symbols or another random letter.

An example of a letter substitution cipher can be seen below, and we are going to solve it!

Cipher 1

Now there are 2 facts about the English language which will help considerably when solving a Cipher.
1 – The most common letter in the English language is E
2 – The most common 3 letter words are ANDTHE

Using the first fact have a look at the cipher above and see what the most common letter here is used?

Cipher 2

We can see that F is the most common Cipher letter, let us initially presume that F equals (This isn’t always the case, so you may need to try other common letters if you find it doesn’t work)…

Cipher 3

Then let’s use this information on the second fact (The most common 3 letter words in the English language are both ANDTHE)

I’ve highlighted below where 3 letters are repeated (MKe is repeated twice and so is ZVC)

Cipher 4

We can make a guess that the MKe one is ‘the‘ and we could also try replacing ZVC with the word ‘and‘.

Cipher 5

and we can now fill in the newly discovered letters and replace all the Z V and C‘s with a, n & d‘s (As per our guess that ZVC is actually the word ‘and‘), and replace all the M & K‘s with t‘s and h‘s (As per our guess that MKe is actually the word ‘the’)

Your Cipher should now look like the below image.

Cipher 6

Now I would say that the assumptions we have made earlier, have come to be true, as this is starting to look like English.
We still have a while to go but we are on the right track, so lets continue!

Now here comes the fun part. We have to study the Cipher and make assumptions.

The easiest one to guess is the Cipher letter that is on its own ‘E


Letters that are usually words on their own are A‘s and I‘s as in ‘I am going to the shops for A drink…’
We can rule out A on the basis that it has been used within the word AND. So we can guess E is actually I
Also we can see there are two 3 letter words ending in ‘he‘ – these are most likely either ‘the‘ or ‘she‘ and seen as we have used ‘the‘ earlier, we can assume it’s ‘she
also we have a 2 letter word beginning with ‘t‘ which is definitely going to be ‘to

Cipher 9
So, lets start replacing those highlighted letters…

Cipher 10

And then we can go through the Cipher replacing the letters with the newly found ones, as below…

Cipher 11

Now we can study and make assumptions, focusing on certain letters which look easy to solve…

Cipher 12

Cipher 13

Focus and assume

Cipher 15Cipher 16

Now we can guess the sentence based on the context…

Cipher 17

 

Congratulations, you have solved your first Cipher! It wasn’t that difficult was it?

Cipher 18

Della

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  • +44 (0) 1472 348909
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