def enc_vigenere(clair, key)
  cipher = ''
  i = 0
  clair.each_byte do |letter|
    cipher += ((((letter - 'A'.ord) + ((key[i % key.length].ord) - 'A'.ord)) % 26) + 'A'.ord).chr
    i += 1
  end
  return cipher
end
 
def dec_vigenere(cipher, key)
  clair = ''
  i = 0
  cipher.each_byte do |letter|
    clair += ((((letter - 'A'.ord) - ((key[i % key.length].ord) - 'A'.ord)) % 26) + 'A'.ord).chr
    i += 1
  end
  return clair
end
 
puts 'V1G3N3R3 3NCRYP70R'
puts
puts 'Encrypt or decrypt ? e/d'
c = gets.chomp
puts
if (c == 'e')
  puts 'Enter the text to encrypt'
  clair = gets.chomp.downcase
  puts
  puts 'Enter the key'
  key = gets.chomp.upcase
  puts
  nclair = ''
  clair.each_byte do |letter|
    case letter
      when 97..122
        nclair += letter.chr.upcase
    end
  end  
  puts enc_vigenere(nclair, key)
elsif (c == 'd')
  puts 'Enter the text to decrypt'
  cipher = gets.chomp.downcase
  puts
  puts 'Enter the key'
  key = gets.chomp.upcase
  puts
  ncipher = ''
  cipher.each_byte do |letter|
    case letter
      when 97..122
        ncipher += letter.chr.upcase
    end
  end  
  puts dec_vigenere(ncipher, key)
else
  puts 'Unknown command'
end
puts
puts 'Type <SPACE> to continue...'
gets

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