How to solve Cryptograms

Cryptograms are puzzles made by consistently substituting each letter (e.g. P) by another (e.g. C). They are usually quotations attributed to famous persons. Here is an example we shall try to solve:-

OH’P YSH HLBH O’Z BCKBOF HS FOA.

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP.

There are a dozen rules (for cryptograms in English) we shall use:-

1. Single letter words are either "A" or "I".

2. A frequent 3-letter word is "THE". Note too, "HE" is a part of "THE".

3. If the penultimate character is an apostrophe, then the word is either a negated verb (like "DON’T" or "CAN’T" ) or the genitive form of a noun like "CAT’S TAIL" or "DOG’S PAW". Thus the letter behind the apostrophe is either a T or an S.

4. A question mark at the end implies that the first word is either WHO, WHAT, WHEN, WHERE, HOW or WHY.

5. Frequent consonant pairs are TH, WH, SH or CH.

6. Frequent word endings are "-TION", "-ENT", "-ANT", "-ING" "-ERS", "-ENS" and "-ED".

7. Short words to which "ING" or "ED" are appended, double up their last consonant. Examples "BEGINNING" or "HOPPED".

8. In 2 letter words one is a vowel.

9. If you are able to guess the author's name (usually given at the end), then that is a great help.

10. Certain word patterns are easy to guess, e.g. X??X is either THAT or ELSE or DEED etc. THAT and ELSE crop up frequently. And ??X?X is usually THERE or WHERE.

11. The pattern X’Y implies X=I and Y=M or Y=D ist. D usually crops up more often than M.

12. If in doubt, guess, and test your guess for consistency elsewhere in the cryptogram.

Using these 12 rules let's tackle the cryptogram puzzle given above:-

OH’P YSH HLBH O’Z BCKBOF HS FOA.

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP.

Rule 3 tells us that "OH’P" is either "IT’S" or "HE’S".

Rule 1 tells us that the "O" at the start of line 2 must be an A or an I.

Both rules together imply O=I, H=T and P=S . Writing the known letters under the code, we get

IT’S ??T T??T I ? ????I? ?T ?I?

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I ??ST ???'T ???T T? ?? T???? ???? IT ??????S

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. ---

Rule 10 tells us that word 3 is probably THAT. So let's substitute L=H and B=A.

IT’S ??T THAT I?? A??AI? T? ?I?

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I T T A T T TH H IT HA

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. --- A

Rule 8 tells us that word 6 must be TO, because no other vowels fits. Rule 11 tells us that Z=M ( since Z occurs only once, it is more likely to be M than D). Rule 3 in word 3 of line 2 tells us that Y=N .

Using rule 10 we guess that the 7th word in the second line must be HLAKA= THERE. Now we have:-

IT’S NOT THAT I'M A RAI TO IE.

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I T ON'T ANT TO E THERE HEN IT HA EN

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. -- OO A EN -- RSSFE BQQAY

Rule 8 tells us that in word 6 of line 2, we can write I=B. Words 4 and 8 of line 2 suggest that R=W . Thus line 2 now reads :-

I T ON'T WANT TO BE THERE WHEN IT HA EN

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. -- WOO A E N -- RSSFE BQQAY

Now we use rule 9. A popular (american) first name is WOODY.

And a probable surname which would fit the pattern would be ALLEN .

So now we have:-

IT’S NOT THAT I'M A RAID TO DIE.

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I T DON'T WANT TO BE THERE WHEN IT HA EN

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. -- WOODY ALLEN -- RSSFE BQQAY

Rule 6 confirms that P=S because T has already been assigned.

Now we have :-

IT’S NOT THAT I'M A RAID TO DIE.

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I ST DON'T WANT TO BE THERE WHEN IT HA ENS.

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP.-- WOODY ALLEN -- RSSFE BQQAY

Taking into account only those letters not yet assigned we now use rule 12 and get:-

IT’S NOT THAT I'M AFRAID TO DIE.

OH’P YSH HLBH O’Z BCKBOF HS FOA.

I JUST DON'T WANT TO BE THERE WHEN IT HAPPENS.

O NDPH FSY’H RBYH HS IA HLAKA RLAY OH LBMMAYP. -- WOODY ALLEN -- RSSFE BQQAY

That was fairly straightforward wasn't it? Now go read my blog please.
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