One Time Pad Algorhitym

[LordBlackout]

Hi all!

I have a problem: I want to implement the One Time Pad Algorhitym in AutoIt, by XORing file's bits with key's bits. The problem is that I have no idea about reading single bits from a file.. any help?

Thanks!

[jchd]

Lookup help for fileopen in binary mode. Read chunks of bytes, perform your xor and write.

[LordBlackout]

Hi, I tried FileOpen in binary mode, but the representation is not binary.. it contains 0-9 digits and some letters, I think is HEX..

Edited April 13, 2011 by LordBlackout

[jaberwacky]

Hex is another way of representing binary numbers.

[LordBlackout]

Yes, I know, but how can I make the XOR with HEX? Is there a way to obtain single bits?

[jchd]

Open input in binary mode

open output in binary mode

read a byte

if eof exitloop

xor with corresponding byte in pad

write result

loop

Hexadecimal is simply a "human-friendly" representation of data. You can display data in hex, octal, ASCII, UTF, whatever suits the need for you to comprehend it. Displaying data under one form or another doesn't change it but some forms give you a better understanding/readability. E.g. displaying text in hex isn't particularly easy to read.

[LordBlackout]

Thanks for the reply, but I don't understand a thing:

Hex contains letters, that are not XORable..

[jchd]

You really should google about things you don't understand.

Look: say you have a file wich contents the string AB3. Ok this is one representation, suited to human eyes and brain.

This ASCII string translates into hex as 41 42 33. This is a second representation, somehow less readable but your brain can still get it if you look at an ASCII table.

In octal, you obtain 101 102 063. This is a fourth representation of the same string. Somehow unusual and much less readable.

In binary, this is 01000001 01000010 00110011. This is a fourth representation of the very same data. Even if you can "read" the series of 0 and 1, it's now much harder to understand that these bits mean AB3.

[LordBlackout]

Thanks for the explanation, but is non this the thing that I don't understand.. I am googling but I can't find a solution:

If I take a byte from a Hex string, let's say "A", how can I XOR this byte? (BitXOR doesn't XOR letters)..

I could transform it in ASCII, but the variable number of digits is a problem when decoding..

[iamtheky]

This ASCII string translates into hex as 41 42 33

so work with that

$string = "AB3"
$Sarray = stringsplit($string , "" , 2)

for $i = 0 to ubound($Sarray) - 1
    $bin = stringtrimleft(binary($Sarray[$i]) , 2)
$Sarray[$i] = $bin
Next

$xor = BitXOR($Sarray[0] , $Sarray[1] , $Sarray[2])

msgbox (0, '' , $Xor)

Edited April 14, 2011 by iamtheky

[LordBlackout]

Thanks, following your example I tried this:

$ID = FileOpen($File, 16)
                $File = StringSplit(StringToBinary(StringTrimLeft(FileRead($ID), 2)), "")
                FileClose($ID)
                $ID = FileOpen($Chiave, 16)
                $Chiave = StringSplit(StringToBinary(StringTrimLeft(FileRead($ID), 2)), "")
                FileClose($ID)
                If $Chiave[0] < $File[0] Then
                    MsgBox(16, "Errore", "La chiave è troppo corta.")
                Else
                    For $a = 3 To $File[0] Step 1
                        $File[$a] = BitXOR($File[$a], $Chiave[$a])
                    Next
                    $File = "0x" & BinaryToString(_ArrayToString($File, "", 1))
                    $ID = FileOpen($NewFile, 18)
                    FileWrite($ID, $File)
                    MsgBox(64, "Info", "Operazione completata con successo.")
                EndIf

But doesn't work.. the file isn't decrypted and becomes unreadable.

Edited April 14, 2011 by LordBlackout

[jaberwacky]

0 1 2 3 4 5 6 7 8 9 A B C D E F

A = 10

B = 11

C = 12

D = 13

E = 14

F = 15