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Re: Re: Re: Icarus

by Adam (Vicar)
on Mar 23, 2001 at 23:16 UTC ( #66707=note: print w/ replies, xml ) Need Help??


in reply to Re: Re: Icarus
in thread Icarus

Yes, you caught the general ideas, but I'll explain the parts you had questions on. Your formating of the code is correct, and the $a assignment is definatly there to throw you, which it didn't.

*$=sub{}; is equivalent to &$=sub{}. This is equivalent to sub $ {}, except that you can't do that. The magic is in the typeglob, which recognizes that its getting an anonymous sub, and names it &$. The value of $$ (the PID) is left unchanged. :-)

Next, you said: sub u(){$_} is the same as sub u { return $_; }, which it isn't. The parens() act as an empty prototype basically telling Perl that the letter u by itself is a valid function call. Otherwise you have to use &u or u(). This allows the u=>u in the next line. Also note that even though this sub is defined inside the scope of the other sub, it is still a package global subroutine - all subroutines are, regardless of where they are defined. Granted there is some magic involved with localized variables and closures, but this doesn't run into any of that.

s[]{82G5S="!A;F]T:&5R(%!E<FP\@:&%C:V5R}six;
Is kind of cool in that it takes $_, which is undefined, and replaces it with the payload, uuencoded. The six are just useless extensions, but distracting ones. Its also sort of a joke in that this was my sixth obfuscation posted here. Note that this will generate a warning about using an undefined variable, but will still pass strict.

And last but not least, die &$=>$/ calls the sub defined earlier, which basically does die unpack( u=>u), $/ Now you asked about $/, it's default value is "\n". If you die with a string ending in a newline, then the "at blah.pl line X" is supressed. That's also true with warn. The u=>u is equivalent to "u", u() where the first u tells unpack to uudecode the return from u(), which just returns $_.

Good job of taking this obfu apart.


Comment on Re: Re: Re: Icarus
Download Code
just a quickie
by larryk (Friar) on Mar 26, 2001 at 14:50 UTC
    Thankyou.

    I have just one other query. You seem to have used => as a comma replacement. I know this is alternate notation when defining a hash but will Perl always interpret this as a comma?

      From perlop

      The => digraph is mostly just a synonym for the comma operator. It's useful for documenting arguments that come in pairs. As of release 5.001, it also forces any word to the left of it to be interpreted as a string.

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