Cryptology

Forums: Science And Math
Email this Topic • Print this Page

The message KYVMR CLVFW KYVBV PZJJV MVEKV VE was encrypted using a shift transformation C congruent to P + k (mod 26). Use frequencies of letters to determine the value of k. What is the plaintext message?

Topic Stats
Top Replies
Link to this Topic

Type: Discussion • Score: 1 • Views: 1,178 • Replies: 7

No top replies

THEVA LUEOF THEKE YISSE VENTE EN (17)

0 Replies

yitwail wrote:

THEVA LUEOF THEKE YISSE VENTE EN (17)

Hi! Thanks for the response. I know that after decrypting the ciphertext the message reads:

The value of the key is seventeen. But I don't see why!

I mean to get this message a shift of 9 does it...

I did this, that is shifted A 9 to the right so the A becomes J and so on:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
J K L M N O P Q R S T U V W X Y Z A B C D E F G I

And after this shift of 9 I got the message you did...

What's the role of 17 here and what's this key doing? Thanks!

0 Replies

RK4 wrote:

yitwail wrote:
THEVA LUEOF THEKE YISSE VENTE EN (17)

Hi! Thanks for the response. I know that after decrypting the ciphertext the message reads:

The value of the key is seventeen. But I don't see why!

I mean to get this message a shift of 9 does it...

I did this, that is shifted A 9 to the right so the A becomes J and so on:

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
J K L M N O P Q R S T U V W X Y Z A B C D E F G I

And after this shift of 9 I got the message you did...

What's the role of 17 here and what's this key doing? Thanks!

Wait a minute. Is this simply 26 - 17 = 9 meaning that start from A and shift 9?

Anyway, how do we get this 17 to begin with:

Let me try...

C = P + k (mod 26), the equal to sign here means congruent to...

V occurs most often in the ciphertext since it has frequency 8

So,...

Let V correspond to the letter E in plaintext since it occurs most often...

So,...

21 = 4 + k (mod 26)

17 = k (mod 26)

k = 17 (mod 26)

so the key, k = 17

and the shift is ... 26 - 17 = 9 from A

Am I right?

0 Replies

The key is either 9 or 17 depending on which direction you shift in. All the plaintext you got tells you is that they used a rotation to the left.

So when someone gives you a caeser shift key without a direction you have to test it in both directions. That is why a shift of 13 is quite popular - as the result is the same whichever direction you apply the shift so direction doesn't matter.

0 Replies

ohnono wrote:

a shift of 13 is quite popular - as the result is the same whichever direction you apply the shift so direction doesn't matter.

which would be a reason to avoid it, if one actually wanted to keep something secret; but of course, shifting all letters a fixed amount won't keep anything secret for all but the simplest messages, like anything more that a couple of words long.

0 Replies

caeser shifts aren't really used for keeping messages secret, but rather to obscure them. The main case where they are used is if you are posting a message in a publically viewed location (such as a forum like this) but want to give people the option of not reading it. For example perhaps the message is the answer to a puzzle, or a spoiler to a movie, or a very rude joke.

0 Replies

now that you mention it, onn, i have seen them used in that fashion.

0 Replies

Cryptology

Related Topics

Quick Links

My Account

able2know