The Vigenère Cipher

Description

  This program uses the Vigenère Cipher to encrypt and cryptanalyze English text. When encrypting English text, simply write the text you want encrypted in the "plaintext" textbox, and the key in the corresponding "key" textbox. You can then press on "Encrypt (All)" which will return ciphertext that includes all the non-letter characters into the "ciphertext" textbox. Alternatively, you can press on "Encrypt (Only letters)" which will return ciphertext with only the letter characters.

  You can also cryptanalyze an English text encoded with the Vigenère Cipher by inputting it in the "ciphertext" textbox. The algorithm for this process is described here. The algorithm can only work effeciently for large sized ciphertext, but the it works well enough that it can often cryptanalyze text of "length" at least 30. In this instance, the "length" of the ciphertext refers to the number of English letters contained in the text. If there is any text in the "key" textbox, the algorithm with only decipher the ciphertext using the given key.