Index of Coincidence

Read this: https://www.dcode.fr/index-coincidence

"Iuhtxhqfb dqdobvlv lv wkh vwxgb ri wkh glvwulexwlrq ri wkh ohwwhuv lq d whaw. Dqdobvlv ri iuhtxhqflhv khos ghfubswlqj vxevwlwxwlrq-edvhg flskhuv xvlqj wkh idfw wkdw vrph ohwwhuv dssdulwlrqv duh ydublqj lq d jlyhq odqjxdjh : lq hqjolvk, ohwwhuv H, W ru D duh frpprq zkloh C ru T duh uduh."

1. Explain how the index of coincidence can be used in cryptography.
2. What are the different types of ciphers described, and what are their index of coincidences listed as?
3. What family of ciphers are used for the following texts?
   1. Jviuyirgc erepcwmw mw xli wxyhc sj xli hmwxvmfyxmsr sj xli pixxivw mr e xibx. Erepcwmw sj jviuyirgmiw lipt higvctxmrk wyfwxmxyxmsr-fewih gmtlivw ywmrk xli jegx xlex wsqi pixxivw ettevmxmsrw evi zevcmrk mr e kmzir perkyeki : mr irkpmwl, pixxivw I, X sv E evi gsqqsr almpi D sv U evi vevi.
   2. Mvpbiabtj duewjgeg zd woi deizm fq woi otgpfzmxamzy cb hyp olxepfo we l wlbe. Lbwzpdlz sq qfaelpqjmpd vazg ohjvjahebx dxiwethqhzzq-iedpr ywgshyw fdwju ksh mene hdok drti wphpsid dwtlcwpwfyv hvp gonmzyj pr l rwrse wdukflua : we pqnptdv, hskehyw P, E cn O rch jsxxcj kytol D zc E wfv cdyi.