How to decode and what is the use?(Math!) • page 1/5 • Off-Topic Discussion • lichess.org

In pure mathematics book I found this question:

MKW PWCCFQ USFGW JOWWM LU FSSARFGKLQC SOWFUW UWQH KWOS XW QWWH PRAW CFOFGMLG ABQFDRBMU XLMK KLCK USWWH OFUWA CBQU

Decode this message received by Space Defence Control

When I found the answer at the last pages in the book, I was shocked!, Like how does this make sense...

In pure mathematics book I found this question: MKW PWCCFQ USFGW JOWWM LU FSSARFGKLQC SOWFUW UWQH KWOS XW QWWH PRAW CFOFGMLG ABQFDRBMU XLMK KLCK USWWH OFUWA CBQU >Decode this message received by Space Defence Control When I found the answer at the last pages in the book, I was shocked!, Like how does this make sense...

BossOfBosses

#2

After this question, I was scared that math will not only be hard for me, but seeming more difficult

Otienimous

#3

THE MEGGAN SPACE FLEET IS APPROACHING PLEASE SEND HELP WE NEED MORE GALACTIC RUNABOUTS WITH HIGH SPEED LASER GUNS. Truthfully, it was really routine decoding, nothing a Space Defence Control with any self-respect should use.

BossOfBosses

#4

OMG! you are right! how do you do that?

Otienimous

#5

First of all, you need to find (guess) the method. Thankfully, the typical cipher for beginners is so-called monoalphabetic substitution cipher. It means that the encrypting person shuffles all the letters of the alphabet and writes it down. Then coding goes as this: you write your message and you change all instances of "a" in the message into the first letter of the shuffled alphabet, all instances of "b" into the second letter and so on. Your shuffled alphabet is the key. If you share it with another person, he or she will decode your message very easily.

And what do you do if you want to break the code without the key? The most efficient method is called "frequency analysis". In the natural language, some letters happen to exist far more often than another ones. For example, in our text we see very numerous instances of W. I expect that the original message was written in English, where the letter E is by far most common. Therefore, I test the substitution W -> E. I see that the first word of the message would be *E ( for unknown letters), so it is very probable that it should be THE indeed. It shows me substitutions M -> T and K -> H. Hence, I see that the word JOWWM is something like **EET. Given the context, there is every chance for FLEET. And so, from the letter to the letter, I break all the code.

Finally, you ask what is the use of this all. Of course, it is the right question: because the monoalphabetic substitution cipher is so easy to break, nobody serious uses it anymore. As far as I remember, the last to try were the Russians during the 1920 Polish-Soviet war - and it didn't end well for them. Despite that, you will encounter this method more often than all the other amateurish coding ideas combined. Therefore, if you (for example) happen to find encrypted messages that your girlfriend exchanged with some unknown guy, and if - as a moral person - you want to read them without tickling her, it is really beneficial to know the trick. Besides, mastering it opens the way to understand far more complicated cryptography. This is why you can find the problem in pure mathematics books, as you already experienced. Nice, isn't it?

First of all, you need to find (guess) the method. Thankfully, the typical cipher for beginners is so-called monoalphabetic substitution cipher. It means that the encrypting person shuffles all the letters of the alphabet and writes it down. Then coding goes as this: you write your message and you change all instances of "a" in the message into the first letter of the shuffled alphabet, all instances of "b" into the second letter and so on. Your shuffled alphabet is the key. If you share it with another person, he or she will decode your message very easily. And what do you do if you want to break the code without the key? The most efficient method is called "frequency analysis". In the natural language, some letters happen to exist far more often than another ones. For example, in our text we see very numerous instances of W. I expect that the original message was written in English, where the letter E is by far most common. Therefore, I test the substitution W -> E. I see that the first word of the message would be **E (* for unknown letters), so it is very probable that it should be THE indeed. It shows me substitutions M -> T and K -> H. Hence, I see that the word JOWWM is something like **EET. Given the context, there is every chance for FLEET. And so, from the letter to the letter, I break all the code. Finally, you ask what is the use of this all. Of course, it is the right question: because the monoalphabetic substitution cipher is so easy to break, nobody serious uses it anymore. As far as I remember, the last to try were the Russians during the 1920 Polish-Soviet war - and it didn't end well for them. Despite that, you will encounter this method more often than all the other amateurish coding ideas combined. Therefore, if you (for example) happen to find encrypted messages that your girlfriend exchanged with some unknown guy, and if - as a moral person - you want to read them without tickling her, it is really beneficial to know the trick. Besides, mastering it opens the way to understand far more complicated cryptography. This is why you can find the problem in pure mathematics books, as you already experienced. Nice, isn't it?

LittleJennyWren

#6

I usually would be ok and interested in this but it's too late at night for me to take in a single word anyone is saying😂😂😂

PepeMaster

#7

This method of deciphering messages without knowing the code helped Elizabeth I to prove the betrayal of her cousin Mary Stuart and cut off her head.
The method was popularized by Poe in his work The Gold-Bug.

This method of deciphering messages without knowing the code helped Elizabeth I to prove the betrayal of her cousin Mary Stuart and cut off her head. The method was popularized by Poe in his work The Gold-Bug.

tpr edited

#8

Julius Caesar used a code like that to dispatch messages by messager about his war in Gaul.

tromeus edited

#9

@Otienimous

Right, the first result when you hit Google MKW PWCCFQ USFGW JOWWM LU FSSARFGKLQC SOWFUW UWQH KWOS XW QWWH PRAW CFOFGMLG ABQFDRBMU XLMK KLCK USWWH OFUWA CBQU is https://math.stackexchange.com/questions/2492498/decode-this-message-received-by-space-defence-control/2492578 with the solution.

The rest that you're writing is correct except that the alphabetical substitution cipher is by all means unbreakable when the correspondence between letters is not 1 to 1.

For example suppose you want to send a message that's been encoded by the 952th verse of Shakespeare's "Othello" onward.

Eg. "And, O you mortal engines, whose rude throats
The immortal Jove's dead clamours counterfeit"

Suppose you want to send something like "I LOVE YOU". The first letter of Shakespeare's verse reads A ( "And, O you mortal engines..." ) so you shift "I" ( "I LOVE YOU" ) 1 place to the right: I becomes J. Second Shakespearean letter is N, so "L" is shifted 14 letters, it becomes Z. Third letter is D, you shift "O" 4 places and so on...

As you can see, no frequency analysis works here because of randomness of substitution ( according to the textual shared key code ) and not 1-1 correspondence.
I'll leave you to guess where this method is used today.

@Otienimous Right, the first result when you hit Google MKW PWCCFQ USFGW JOWWM LU FSSARFGKLQC SOWFUW UWQH KWOS XW QWWH PRAW CFOFGMLG ABQFDRBMU XLMK KLCK USWWH OFUWA CBQU is https://math.stackexchange.com/questions/2492498/decode-this-message-received-by-space-defence-control/2492578 with the solution. The rest that you're writing is correct except that the alphabetical substitution cipher is by all means unbreakable when the correspondence between letters is not 1 to 1. For example suppose you want to send a message that's been encoded by the 952th verse of Shakespeare's "Othello" onward. Eg. "And, O you mortal engines, whose rude throats The immortal Jove's dead clamours counterfeit" Suppose you want to send something like "I LOVE YOU". The first letter of Shakespeare's verse reads A ( "And, O you mortal engines..." ) so you shift "I" ( "I LOVE YOU" ) 1 place to the right: I becomes J. Second Shakespearean letter is N, so "L" is shifted 14 letters, it becomes Z. Third letter is D, you shift "O" 4 places and so on... As you can see, no frequency analysis works here because of randomness of substitution ( according to the textual shared key code ) and not 1-1 correspondence. I'll leave you to guess where this method is used today.

giulatestacoglione

#10

@tromeus yes when you discover some letter as @Otienimous already explained you can make hypotesis on the entire word...then by tryal and error you can solve it