Re: How do I apply the index of coincidence?

Hmmm. Ok. So what is the first step in determining the plaintext from
the ciphertext "OPKWWECIYOPKWIRG"? If I understand the process
correctly, the key length must be determined.

On slide 35 it looks like the IC must be calculated to find likely
values of key length. The IC I get for "OPKWWECIYOPKWIRG" is
0.0583333333333. From slide 35 it appears that the likely key length is
2. Am I on the right track?

If I have this right so far, the ciphertext must be split into two
Alphabet 0:OKWCYPWR
Alphabet 1:PWEIOKIG

Now I'm stuck on determining the key. Any suggestions on how to
determine the key? Thanks!