Vigenère Cipher

As the video we watched several slides earlier informed us, the Vigenère cipher isn't immune to frequency analysis.

You can break cipher text encrypted with the Vigenère cipher by:

1. Finding the length, L, of the keyword that was used for the encryption (What did the video say we need to do to find this length?)
2. Dividing the letters in the text into groups: letters at spots 1, L + 1, 2L + 1, 3L + 1, etc., will go into group 1, letters at spots 2, L + 2, 2L + 2, 3L + 2, etc., will go into group 2, etc.
3. Performing frequency analysis on each of the groups.
4. Substituting the plaintext letters that you found as part of the frequency analysis back into the encrypted text to get the whole plaintext.

Remember: The Vigenère cipher is just a combination of several Caesar ciphers.