Re^2: Malicious Code

[bunnyman]

The key is the y///. The code simplifies into this:

$_ = '=]=>%-{<-|}<&|`{';
y/ -\/:-@[-`{-}/`-{~" -/;

The y operator is the same thing as the tr operator. The mapping looks like this:

 -/:-@[-`   --->    `-{~
      {-}   --->    " -

That's the range of space through forward-slash, concatented with the range of colon through at-sign, and left-square-bracket through backquote, maps onto the range from ` to left-curly-bracket, plus the tilde character. If we check the ASCII character set, we can simplify this into:

 -/       --->    `-o
:-@       --->    p-v
[-`       --->    w-{~
 {        --->    "
 |        --->    space
 }        --->    -

So now, we can rewrite this as:

$_ = '=]=>%-{<-|}<&|`{';
tr/!-\//a-o/;
 tr/:-@/p-v/;
 tr/[-^/w-z/;
 tr/`/~/;
 tr/{/"/;
 tr/|/ /;
 tr/}/-/;
print;

It's just a sneaky way to map punctuation characters into alphabet letters.