VMS coincidence index (vigenere cipher test)

["Anders, Claus" <canders@xxxxxxxxx>]

Hi all,
rereading old vms mails today, I read one concerning vigenere cipher. I
wondered how to solve such ciphers and found a method call coincident index
on the net. I applied this algorithm to the vms and found, that (after
removing all ".*,-!%" chars) there is a strong max value for index at 4,5,6
or 7 ( more than 10% coincidence). This could suggest a key-length from 5 to
6 .
Any comments ?
Claus