Ruby 8 bit S-DES encryption

Ruby_Encryption.rb

# Ruby_Encryption.rb

#Shifts each half of number left one
def shift(number)
  first_perm = ""
  second_perm = ""
  
  for i in 0..3
    first_perm += number[i + 1]
    second_perm += number[i + 6]
  end
  
  first_perm += number[0]
  second_perm += number[5]
  finish = first_perm
  finish += second_perm
  
  return finish
end

#Creates an 8 digit key out of 4 digits
def ep(permute)
  change = [3,0,1,2,1,2,3,0]

  finish = ""
  for i in 0..7
    finish += permute[change[i]]
  end
  
  return finish
end

#Uses a premade permutation to change the order of the input
def p10(number)
  change = [2,4,1,6,3,9,0,8,7,5]
  finish = ""
  
  for i in 0..9
    finish += number[change[i]]
  end
  
  return finish
end

#Pulls in 10 bits, changes order and cuts out the first two bits
def p8(number)
  change = [5,2,6,3,7,4,9,8]
  finish = ""
  
  for i in 0..7
    finish += number[change[i]]
  end
  
  return finish
end

#Uses a premade permutation to change the order of the input
def p4(number)
  change = [1,3,2,0]
  finish = ""
  
  for i in 0..3
    finish += number[change[i]]
  end
  
  return finish
end

#Uses a premade permutation to change the order of the input
def ip(plaintext)
  change = [1,5,2,0,3,7,4,6]
  finish = ""
  
  for i in 0..7
    finish += plaintext[change[i]]
  end
  
  return finish
end

#Uses a premade permutation to change the order of the input
def ip1(number)
  change = [3,0,2,4,6,1,7,5]
  finish = ""
  
  for i in 0..7
    finish += number[change[i]]
  end
  
  return finish
end

#Switches the first half and last half of an 8 bit sequence
def sw(number)
  finish = "    "
  
  for i in 0..3
    finish[i] = (number[i + 4])
	finish += number[i]
  end
  
  return finish
end

def s0(plaintext)
  array = [[1,0,3,2],
           [3,2,1,0],
		   [0,2,1,3],
		   [3,1,3,2]]
		   
    t_row = plaintext[0]
	t_row += plaintext[3]
	
	t_col = plaintext[1]
	t_col += plaintext[2]
	
	hold = array[t_row.to_i(2)][t_col.to_i(2)]
	
	if hold == 0
	  hold = "00"
	elsif hold == 1
	  hold = "01"
	else
	  hold = hold.to_s(2)
	end
	
	return hold   
end

def s1(plaintext)
  array = [[0,1,2,3],
		   [2,0,1,3],
		   [3,0,1,0],
		   [2,1,0,3]]
		   
    t_row = plaintext[0]
	t_row += plaintext[3]
	
	t_col = plaintext[1]
	t_col += plaintext[2]
	
	hold = array[t_row.to_i(2)][t_col.to_i(2)]
	
	if hold == 0
	  hold = "00"
	elsif hold == 1
	  hold = "01"
	else
	  hold = hold.to_s(2)
	end
	
	return hold  
end

def exor(plaintext, primekey)
  count = plaintext.length
  finish = "" 
  for i in 0...count
    if plaintext[i] == primekey[i]
	  finish += "0"
	else
	  finish += "1"
	end
  end
  
  return finish
end

def encrypt(plaintext, number)
  newplaintext = ip(plaintext)
  fk = ""
  permute = ""
  permute1 = ""
  permutehold = ""
  
  #Getting two keys
  key1 = p10(number)
  key1 = shift(key1)
  key2 = key1
  key1 = p8(key1)
  key2 = shift(key2)
  key2 = shift(key2)
  key2 = p8(key2)
  
 for i in 0..3
    fk += newplaintext[i]
	permute += newplaintext[i + 4]
	permutehold += newplaintext[i + 4]
  end
  
  newplaintext = ep(permute)
  newplaintext = exor(newplaintext, key1)
  
  for i in 0..3
    permute1 += newplaintext[i]
	permute[i] = newplaintext[i + 4]
  end
  
  byte = s1(permute)
  byte1 = s0(permute1)
  byte1 += byte
  byte = p4(byte1)
  
  newplaintext = exor(fk, byte)
  newplaintext += permutehold
  newplaintext = sw(newplaintext)

#Process repeats with second key and an ip1 call at the end
  
  for i in 0..3
    fk[i] = newplaintext[i]
	permute[i] = newplaintext[i + 4]
	permutehold[i] = newplaintext[i + 4]
  end
  
  newplaintext = ep(permute)
  newplaintext = exor(newplaintext, key2)
  
  for i in 0..3
    permute1[i] = newplaintext[i]
	permute[i] = newplaintext[i + 4]
  end
  
  byte = s1(permute)
  byte1 = s0(permute1)
  byte1 += byte
  byte = p4(byte1)
  newplaintext = exor(fk, byte)
  newplaintext += permutehold
  newplaintext = ip1(newplaintext)
  
  return newplaintext
end

def decrypt(ciphertext, number)
  newciphertext = ip(ciphertext)
  fk = ""
  permute = ""
  permute1 = ""
  permutehold = ""
  
  #Getting two keys
  key1 = p10(number)
  key1 = shift(key1)
  key2 = key1
  key1 = p8(key1)
  key2 = shift(key2)
  key2 = shift(key2)
  key2 = p8(key2)
  
 for i in 0..3
    fk += newciphertext[i]
	permute += newciphertext[i + 4]
	permutehold += newciphertext[i + 4]
  end
  
  newciphertext = ep(permute)
  newciphertext = exor(newciphertext, key2)
  
    
  for i in 0..3
    permute1 += newciphertext[i]
	permute[i] = newciphertext[i + 4]
  end
  
  byte = s1(permute)
  byte1 = s0(permute1)
  byte1 += byte
  byte = p4(byte1)
  
  newciphertext = exor(fk, byte)
  newciphertext += permutehold
  newciphertext = sw(newciphertext)

#Process repeats with second key and an ip1 call at the end
  
  for i in 0..3
    fk[i] = newciphertext[i]
	permute[i] = newciphertext[i + 4]
	permutehold[i] = newciphertext[i + 4]
  end
  
  newciphertext = ep(permute)
  newciphertext = exor(newciphertext, key1)
  
  for i in 0..3
    permute1[i] = newciphertext[i]
	permute[i] = newciphertext[i + 4]
  end
  
  byte = s1(permute)
  byte1 = s0(permute1)
  byte1 += byte
  byte = p4(byte1)
  newciphertext = exor(fk, byte)
  newciphertext += permutehold
  newciphertext = ip1(newciphertext)
  
  return newciphertext
end

#   65% of original code size
key = "1000110101"
passed = false

while passed == false
  print "Encrypt or Decrypt: "
  choice = gets.chomp
  
  if choice == "Encrypt"
    output = ""
    File.open('Ruby_Plaintext.txt', 'r') do |text|
	  read_in = text.read.split(" ")
	  
	  read_in.each do |plaintext|
	    ciphertext = encrypt(plaintext, key)
		output += ciphertext + " "
	  end
	end
	print "Encrypted"
	File.open('Ruby_Ciphertext.txt', 'w') { |file| file.write(output) }
    passed = true
  elsif choice == "Decrypt"
    output = ""
    File.open('Ruby_Ciphertext.txt', 'r') do |text|
	  read_in = text.read.split(" ")
	  
	  read_in.each do |ciphertext|
	    plaintext = decrypt(ciphertext, key)
		output += plaintext + " "
	  end
	end
	print "Decrypted"
	File.open('Ruby_Decrypt.txt', 'w') { |file| file.write(output) }
    passed = true
  end
end