Released : 2015-11-21 16:15:45 -0500
Viewed : 955
Contrary to popular belief, in Cryptography, breaking a cipher is not the process of finding plaintext relating to a ciphertext. Breaking a cipher (Cryptanalysis) is the process of finding the Key used to encrypt a data. Once a Key is found, many instances of data can be decrypted. That's why in modern ciphers, even if you know the plaintext (or even select it), you should not be able to find the Key.
Vigenere is one of Classical Cipher, that rotate character based on key's characters.
Our task is to find the key. So the trick here is to rotate the key 'only' 1 time with character 'A'. While the "Key Length" we don't know yet, let just put 20 characters in the field.
And we got the key :)