Finding the last flag is hard ? please, someone can help me? I think I found the right ciph** type and the right length of the key (10) but not sure how to decode it… I tried different sites without success.
Update: I have the right length and the right ciph** now but I’m not sure about the alphabetical letters to use…
Update2: Got it!! And I found it!! 
hint: search “Letters frequency Analysis Tool”, it could help you (a lot!) and playing with frequencies