Need help with part of PHP code - encryption!

[Malyghos]

Hello,

I have one line that I can't understand of PHP code used to encrypt strings:

$temp = ord(substr($str,$i,1)) ^ 203;

I understand everything but this " ^203 "

Can you explain me what it does?

[Adam]

"^" is a bitwise operator called Xor (exclusive or), that basically checks the bits between the given arguments, and sets all the bits to 1 where they're only set to 1 in one of the arguments.

 

As a quick example:

 

1001 ^ 1000 = 0001

 

.. Because the first bit is set in both arguments, but the last bit is only set in the first.

[Malyghos]

Thank you very much!

I am doing this manually.

So, should I change ORD(whatever) and 203 to binary and then XOR them?

[Adam]

I'm not sure. What are you trying to do? ord(whatever) and 203 would be be compared at bit-level by the Xor operator.

[johnny86]

It is a bitwise operator http://fi.php.net/manual/en/language.operators.bitwise.php

 

And it compares binary values of two numbers. It searches for bits that are set in only one of the numbers. For example binary for 5 = 0101 and binary for 8 = 1000

 

so in comparsion of 5 ^ 8 = 13

 

because

       BITS
5:    0 1 0 1
8:    1 0 0 0 
R:    1 1 0 1  and decimal value for 1101 = 13

6:    0 1 1 0
7:    0 1 1 1
R:    0 0 0 1 and decimal value for 0001 = 1

so 5 ^ 8 = 13
and 6 ^ 7 = 1

same result with 8 ^ 5  or 7 ^ 6 because bits dont change. They are just compared. And depends on which operator you use what it will return.

 

You dont have to change your numbers because bitwise operators compare the numbers in binary-level.