Step by Step solution about How to resolve the algorithm Playfair cipher step by step in the Ruby programming language

This Ruby code implements the Playfair cipher, a classic encryption algorithm. Let's break down the code step by step:

Class Playfair: This class encapsulates the Playfair cipher's functionality. Size: A constant representing the size of the 5x5 grid used in the cipher. initialize(key, missing): The initializer takes two parameters: key, which is the encryption key, and missing, which specifies a single missing letter (typically 'J'). alphabet: A string containing the English alphabet, excluding the missing letter. extended: Combines the key with the alphabet, removing duplicates, and limiting the length to the 5x5 grid size (25 characters). grid: Creates a 5x5 grid from the extended alphabet. coords: A hash that maps each letter in the grid to its (row, column) coordinates. @encode: A hash that maps letter pairs to their encrypted counterparts. @decode: The inverse of @encode, used for decryption. encode(plaintext): Encodes the given plaintext using the Playfair cipher. plain: Preprocesses the plaintext by converting it to uppercase, removing non-alphabetic characters, and replacing 'J' with 'I' or 'X' depending on the missing letter. plain is modified to ensure pairs of identical letters have an 'X' inserted between them. If the plaintext length is odd, an 'X' is appended. The plaintext is split into pairs and passed through the @encode hash to get the corresponding encrypted pairs. decode(ciphertext): Decrypts the given ciphertext using the inverse Playfair cipher. cipher: Preprocesses the ciphertext in a similar way to encode(). The ciphertext is split into pairs and passed through the @decode hash to get the corresponding decrypted pairs. Usage Example: To encrypt a message "HELLOWORLD" with the key "KEYWORD" and missing letter 'J', you can create an instance of Playfair and call the encode() method: require 'playfair.rb' playfair = Playfair.new("KEYWORD", "J") encrypted = playfair.encode("HELLOWORLD") Similarly, to decrypt the encrypted message, call the decode() method: decrypted = playfair.decode(encrypted) In summary, this code provides a robust implementation of the Playfair cipher, allowing you to encrypt and decrypt messages using a given key and missing letter.

class Playfair
  Size = 5
  def initialize(key, missing)
    @missing = missing.upcase
    alphabet = ('A'..'Z').to_a.join.upcase.delete(@missing).split''
    extended = key.upcase.gsub(/[^A-Z]/,'').split('') + alphabet
    grid = extended.uniq[0...Size*Size].each_slice(Size).to_a
    coords = {}
    grid.each_with_index do |row, i|
      row.each_with_index do |letter, j|
       coords[letter] = [i,j]
      end
    end
    @encode = {}
    alphabet.product(alphabet).reject { |a,b| a==b }.each do |a, b|
      i1, j1 = coords[a]
      i2, j2 = coords[b]
      if i1 == i2 then
         j1 = (j1 + 1) % Size
         j2 = (j2 + 1) % Size
      elsif j1 == j2 then
         i1 = (i1 + 1) % Size
         i2 = (i2 + 1) % Size
      else
         j1, j2 = j2, j1
      end
      @encode["#{a}#{b}"] = "#{grid[i1][j1]}#{grid[i2][j2]}"
      @decode = @encode.invert
    end
  end

  def encode(plaintext) 
    plain = plaintext.upcase.gsub(/[^A-Z]/,'')
    if @missing == 'J' then
      plain = plain.gsub(/J/, 'I')
    else
      plain = plain.gsub(@missing, 'X')
    end
    plain = plain.gsub(/(.)\1/, '\1X\1')
    if plain.length % 2 == 1 then
      plain += 'X'
    end
    return plain.upcase.split('').each_slice(2).map do |pair|
      @encode[pair.join]
    end.join.split('').each_slice(5).map{|s|s.join}.join(' ')
  end

  def decode(ciphertext) 
    cipher = ciphertext.upcase.gsub(/[^A-Z]/,'')
    return cipher.upcase.split('').each_slice(2).map do |pair|
      @decode[pair.join]
    end.join.split('').each_slice(5).map{|s|s.join}.join(' ')
  end
end