Question

The following ciphertext was generated using the Vignere method with a key length at most 6. If anyone would be willing to decrpyt it and describe all steps of their thought process and how the results guided you towards the key would be greatly appreciated it! Also, comment on what is unusual about the plaintext and how did it affect the results:

hdsfgvmkoowafweetcmfthskucaqbilgjofmaqlgspvatvxqbiryscpcfrmvswrvnqlszdmgao

qsakmlupsqforvtwvdfcjzvgsoaoqsacjkbrsevbelvbksarlscdcaarmnvrysywxqgvellcyl

uwwveoafgclazowafojdlhssfiksepsoywxafowlbfcsocylngqsyzxgjbmlvgrggokgfgmhlm

ejabsjvgmlnrvqzcrggcrghgeupcyfgtydycjkhqluhgxgzovqswpdvbwsffsenbxapasgazmy

uhgsfhmftayjxmwznrsofrsoaopgauaaarmftqsmahvqecevvfsifzpbumppndzeneeb

Answer 1

The easiest way is to have a double-entry grid,

Google it to find the Vigenere Cipher using a table

When the alphabet is ABCDEFGHIJKLMNOPQRSTUVWXYZ

Locate the first letter of the plaintext message in the first line of the table and the first letter of the key on the left column. The cipher letter is at the intersection.

How to decrypt Vigenere cipher?

Vigenere decryption requires a key (and an alphabet). As for encryption, two ways are possible.

Decryption of Vigenere by subtracting letters

Example: To decrypt NGMNI, the key is KEY and the alphabet is ABCDEFGHIJKLMNOPQRSTUVWXYZ.

To decrypt, take the first letter of the ciphertext and the first letter of the key, and subtract their value (letters have a value equals to their position in the alphabet starting from 0). If the result is negative, add 26 (26=the number of letters in the alphabet), the result gives the rank of the plain letter.

Example: Take the first letters of the ciphertext N (value = 13) and the key K (value = 10) and subtract them (13-10=3), the letter of value 3 is D.

Continue with the next letters of the message and the next letters of the key, when arrived at the end of the key, go back the the first key of the key.

Example: NGMNI
KEYKE

Example: DCODE is the plain text.