straddling checkerboard with ruby

azwan ali — Sun, 31 Jan 2010 11:48:29 +0000

this week i sharpen my ruby saw with an excessive about straddling checkerboard encryption.

In cryptography, a straddling checkerboard is a device for converting an alphabetic plaintext into digits whilst simultaneously achieving fractionation (a simple form of information diffusion) and homophony (a simple method for suppressing peaks of the frequency distribution). It also is known as a monome-dinome cipher. -- wikipedia

after do some reading on how the operation was, i've workout the algorithm.
as i want to learn more about ruby but don't know what i can do with it, so i decided to write this in ruby

here's the solution

class Straddling
def initialize( key_text, n1, n2, n3 )
key_text = key_text+"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
key_text = key_text.upcase.split(//).uniq
@key_text = key_text
@n1 = n1;@n2 = n2;@n3 = n3
end
def create
@board = Array.new()
k = 0;prev = ""
for a in 0..40 do
if (a == @n1 || a == @n2 || a == @n3)
@board[a] = "_"
else
if ("A".."J") === prev
@board[a] = prev == "J"? 0:((prev)[0]-16).chr
else
@board[a] = @key_text[k] == " " ? "*" : @key_text[k]
k+=1
end
prev = @board[a]
end
end
return @board.to_s
end
def tp(key,text)
@key = key.split(//)
@text = text.gsub(' ','*').upcase.split(//)
end
def keygen
@keygen = Array.new
@checker_board = @board.to_s.split(//)
for a in 0..@text.length-1 do
found = @checker_board.index(@text[a])
if (0..9) === found
@keygen.push(found)
elsif (10..19) === found
@keygen.push(@n1,found%10)
elsif (20..29) === found
@keygen.push(@n2,found%10)
else
@keygen.push(@n3,found%10)
end
end
end
def e(key,text)
self.tp(key,text)
self.keygen
print "#{@keygen.to_s}\n"
t = Array.new
@keygen.each do |value|
t.push((@key[0].to_i+value.to_i)%10)
@key << @key.shift
end
print "#{@t.to_s}\n"
print "Encrypt=#{self.show(t)}\n"
end
def d(key,text)
self.tp(key,text)
self.keygen
t = Array.new
@keygen.each do |value|
t.push((value+10-(@key[0]).to_i)%10)
@key << @key.shift
end
print "Decrypt=#{self.show(t).gsub('*',' ')}\n"
end
def show(t)
a = 0
result = ""
while a < t.length
unless t[a] == @n1 || t[a] == @n2 || t[a] == @n3
result = result + @checker_board[t[a]]
a+=1
else
result = result + @checker_board[t[a+1]==nil ?
t[a]:(t[a]==@n1 ?1:(t[a]==@n2) ?2:3)*10+t[a+1]]
a+=2
end
end
return result
end
end
board = Straddling.new("sharpen your saw",2,5,9)
puts(board.create)
board.e("2641","programming praxis")
board.d("2641","S811R53S87A18RUAS8PSSH5")
puts("\n")
board.e("2641","encrypt this text")
board.d("2641","A118R1H81A8RALR8H5ALRA180_")
puts("\n\n")
board = Straddling.new("my secret keys",2,5,9)
puts(board.create)
board.e("241","ruby programming rocks")
board.d("241","SF5E5*5MIREESEACY45YIS5****MESE")

code preview
fix: bug where it didn't check for null value after last digit
note that this code use 3 space but of course you can modify it and chose different space if you like

i cant think » cryptography

straddling checkerboard with ruby