Module: Cryptools::Cryptanalysis

Defined in:
lib/cryptools.rb

Class Method Summary collapse

Class Method Details

.english_freq_count(str) ⇒ Object 



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# File 'lib/cryptools.rb', line 71

def english_freq_count(str)
  str.scan(/[ETAOIN SHRDLU]/i).length
end

.index_of_coincidence(input) ⇒ Object 



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# File 'lib/cryptools.rb', line 56

def index_of_coincidence(input)
  fs = input.each_with_object(Hash.new(0)) { |word,counts| counts[word] += 1 }
  phiO = 0
  n = input.length
  coin_rtext = 0.0385

  fs.each {
    |key, f|
    phiO += f * (f - 1)
  }

  phiR = coin_rtext * n * (n - 1) 
  phiO / phiR
end