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Vigenere Decryption with key length

ru flag

I have a question. If I have 2 ciphertexts given and the same key has been used on both. They key lenght is the same as the plaintext and cipherrtext length. How do I decrypt them and find the key. So far I know that c1 + c2 = p1 + p2.

kelalaka avatar
in flag
You might use crib-dragging, however, have you tried Kasiski's test and some online tools?
ru flag
I have not heard of Kasiski'test as I am in week 5 of Computer Security module in uni but I tried almost every online tool I could find and it does not give me any results that match words from english launguage.
kelalaka avatar
in flag
https://www.dcode.fr/vigenere-cipher
ru flag
I used that and put in my 2 ciphertexts, then pressed decrypt with key length, which I know is 10 and not a single of the results is an actual English word.
kelalaka avatar
in flag
Kasiski's test is used to determine the length of the key. Once you ask for the decrypt wiht 10, there the results are a huge list. Hint: append the the texts while striping the first one to mod 10.
ru flag
I know the key length is 10. I have already gone through all hte results displayed on the page and none of are actual words. I have appended them and got the result, somewhere in the lecture said that ct1+ct2=p1+p2 (ct=ciphertext, p=plaintext) but I have no idea where to go from there.
kelalaka avatar
in flag
That is crib dragging, however, you might be given a lead (hint).
ru flag
1 hour of thinking and I am still nowhere :( I dont see what hint I get from the append.
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