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rot13 Jan 1 2006, 03:26 AM
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sas01
Dec 31 2005, 05:46 PM
I'm slightly confused :s if I wanted to write my name it would be

Code:
 

SHONONREKNGREPEONGRE
AHTRNHOPROPGNRTNHHPR
SGOTHPTRHOT?HOPT?HOR
04040346352543LOGOP34?
1432546454H6H65H7II67I


Ok that's all easy what I don't understand is this
Quote:
 

Then to encrypt a message like "til the cows come home" you encrypt the first letter using the C line, the next letter using the O line, and so on. Here is the message with the line used to encrypt it written below:
CODE

TIL THE COWS COME HOME
COW SCO WSCO WSCO WSCO

so for line C, T is encrypted as V
for line O, I is encrypted as W
for line W, L is encrypted as H
for line S, T is encryptes as L,
for line C, H is encrypted as J
for line O, E is encrypted as S
...and so forth

The final encrypted message, with word breaks preserved, would be:
VWH LJS YGYG YGOS DGOS

Notice the repeating YGYG YG. That's an interesting thing. With Vigenere, encrypting C with a key of W is the same as encrypting W with a key of C. The word COWS is encrypted with a key of WSCO. So CO with a key of WS encrypts as YG. Likewise, WS with a key of CO also encrypts as YG.


Can anyone explain to me please?

Okay, first of all, a typical Vigenere cipher only uses letters, so the 01 at the end of your name wouldn't count. Second, Vigenere is done by shifting a regular A-Z alphabet by different positions. To make a key from your name, at least the SAS part, you create three alphabets, the first and last starting with S, wrapping around and finally ending at R. The middle alphabet, since it starts with A would be a regular A-Z alphabet:

Code:
 

STUVWXYZABCDEFGHIJKLMNOPQR
ABCDEFGHIJKLMNOPQRSTUVWXYZ
STUVWXYZABCDEFGHIJKLMNOPQR


Notice that your name appears if you look at the first letter in each row.

You have three alphabets to work with. You encode the 1st letter with the first alphabet, the second letter with the second alphabet, the third letter with the third alphabet ,and then the fourth letter goes back to the first alphabet.

To encode a letter with the first alphabet, you can write it like this:
Code:
 

PLAIN:  ABCDEFGHIJKLMNOPQRSTUVWXYZ
CIPHER: STUVWXYZABCDEFGHIJKLMNOPQR

So to encrypt a letter, you look on the Plain line to find the letter. The encrypted letter is the one below it. For example, C is encrypted as U, F is encrypted as X, and so on. Now, on your middle alphabet, since it starts with A, the letters aren't really encrypted since A encrypts as A, B as B and so on.

Going back to the previous example, the sentence to be encrypted was "TIL THE COWS COME HOME"
I wrote "COW SCO WSCO WSCO WSCO" underneath it to indicate which alphabet to use. The alphabet beginning with C works like this:

Code:
 

Plain:  ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher: CDEFGHIJKLMNOPQRSTUVWXYZAB

I said that T is encrypted as V. To get that, I looked at the Plain line, found T, then looked for the letter beneath it, which was V.

For the O alphabet, you have:
Code:
 

Plain:  ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher: OPQRSTUVWXYZABCDEFGHIJKLMN

I want to encrypt I, and I see that W appears under it, so I is encrypted as W.

I hope that makes sense.
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