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

The provided code implements both encryption and decryption using the Polybius square cipher in Ruby. The Polybius square is a 5x5 grid filled with the letters of the alphabet, used for encrypting messages by replacing each letter in the message with the row and column numbers of the corresponding letter in the square.**

Here's a detailed explanation of the Ruby code:

1. Clean Message:

   • The cleanMsg method takes two parameters: msg (the message to be processed) and square (the Polybius square).
   • It converts the msg to uppercase and removes all spaces.
   • If the J character is not present in the square, it removes all occurrences of J from the message.

2. Encryption:

   • The encrypt method takes two parameters: msg (the message to be encrypted) and square (the Polybius square).
   • It first calls cleanMsg to prepare the message for encryption.
   • It calculates the size of the square using the square root of its length.
   • It initializes two arrays, rows and cols, each with the same length as the message.
   • It iterates over each character in the message and finds its position in the Polybius square using the index method.
   • It assigns the row and column numbers of the character to the corresponding elements in rows and cols.
   • Finally, it concatenates rows and cols and iterates over the resulting array in pairs. For each pair, it takes the row and column numbers and uses them to retrieve the corresponding character from the Polybius square, building the encrypted message.

3. Decryption:

   • The decrypt method takes two parameters: msg (the encrypted message) and square (the Polybius square).
   • It converts both msg and square to uppercase.
   • It calculates the size of the square as before.
   • It initializes an empty array coords to store the row and column numbers of the encrypted characters.
   • It initializes an empty string result to store the decrypted message.
   • It iterates over each character in the encrypted message and finds its position in the Polybius square.
   • It appends the row and column numbers of the character to the coords array.
   • Finally, it iterates over the coords array in pairs of two, taking the row and column numbers and using them to retrieve the corresponding character from the Polybius square, building the decrypted message.

4. Print Square:

   • The printSquare method takes one parameter: square (the Polybius square).
   • It calculates the size of the square as before.
   • It iterates over the square, taking slices of size sq_size (the number of columns) and printing each slice on a new line. This visualizes the Polybius square.

5. Test Cases:

   • The code includes a list of test cases, each consisting of a message and a Polybius square.

6. Main Loop:

   • The code iterates over each test case, printing the Polybius square, the original message, the encrypted message, and the decrypted message.

In summary, this code implements a Polybius square cipher in Ruby, allowing for both encryption and decryption of messages using a provided Polybius square.

def cleanMsg(msg, square)
  msg.upcase!
  msg.delete!(' ')
  msg.delete!('J') if square.index('J') == nil
end

def encrypt(msg, square)
  cleanMsg msg, square
  sq_size = (square.length ** 0.5).to_i
  rows = [0] * msg.length
  cols = [0] * msg.length
  (0...msg.length).each do |i|
    p = square.index(msg[i])
    rows[i], cols[i] = p / sq_size, p % sq_size
  end
  result = ""
  rows.concat(cols).each_slice(2) do |coord|
    result += square[coord[0]*sq_size + coord[1]]
  end
  return result
end

def decrypt(msg, square)
  msg.upcase!; square.upcase!
  sq_size = (square.length ** 0.5).to_i
  coords = []
  result = ""
  (0...msg.length).each do |i| 
    p = square.index(msg[i])
    coords << p / sq_size
    coords << p % sq_size
  end
  for i in (0...coords.length/2) do
    row, col = coords[i], coords[i+coords.length/2]
    result += square[row*sq_size + col]
  end
  return result 
end

def printSquare(square)
  sq_size = (square.length ** 0.5).to_i
  (0..square.length).step(sq_size).each do |i|
    print square[i...(i+sq_size)], "\n"
  end
end

tests = [["ATTACKATDAWN" , "ABCDEFGHIKLMNOPQRSTUVWXYZ"],
         ["FLEEATONCE"   , "BGWKZQPNDSIOAXEFCLUMTHYVR"],
         ["ATTACKATDAWN" , "ABCDEFGHIKLMNOPQRSTUVWXYZ"],
         ["the invasion will start on the first of january", "BGWKZQPNDSIOAXEFCLUMTHYVR"],
         ["THIS MESSAGE HAS NUMBERS 2023", "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"],
]

for test in tests
  message = test[0]; square = test[1];
  encrypted = encrypt(message, square)
  decrypted = decrypt(encrypted, square)

  puts "using the polybius:"
  printSquare(square)
  puts "the plain message:", message 
  puts "encrypted:", encrypted 
  puts "decrypted:", decrypted 
  puts "===================================================="
end