- 7, 0x7, 00000111
- 246,0xd6, 11010110
- 1050,0x41a 010000011010
- 98765,0x181cd, 00010100000111001101
The magical property of Xor ^
If we xor two ints a and b to get c then a ^ c gives b and b ^ c gives a.To create an encrypted text file, "binary xor" a file of text with a value, say 255 to get an encrypted file. If we xor this with 255, we get back our original unencrypted text. As encryption schemes go, this is light weight and probably the most reinvented wheel by novice programmers. It can be made tougher by using values to xor that have at least 3 bits set instead of just 255.
In 8 bits, there are 256 different possible values- 0 to 255. There are only 36 values with 0,1, OR 2 set bits so that leaves 219 values which can be used. Stick these in an array and xor the first byte of the file against the first byte of the table, 2nd against the 2nd array value and so on.
Although light weight it is useful for hiding text strings in applications. A binary file viewer/editor lets anyone look for text strings, hidden commands, registry keys, even secret passwords. By encrypting these it makes life harder for them.
Example 3 displays the 219 values with three or more bits set, plus the remainder. It uses a similar mechanism to that PrintBinary() used in example 1.
Download Example 3.
On the next page - A look at Unions
