[Help]C++ evaluate () function

[.::SCHiM::.]

Hey guys, what's up??

I've been diving into executable protection and things like that and I find that I'm being limited by C++'s static linking ( I cannot modify the code while running)

Remember that little [TEST] thread of mine a while ago? I said I used techniques that would modify my code on the fly, it turned out that I was being tricked by my own program. There was nothing realy special about it.

I want to be able to change the way my program encrypts and thus decrypts itself every time it runs. I thought I had completed my objective but I was wrong...

Now I'm trying it again, and I want to do it like this:

I've read about a function called eval(), that exists in certain languages. The eval function would execute a string as code (!)

say this is an sample of a non-existant language:

var i = 1

echo( eval("i = i + i") )

The program would take the string "i = i + i" and execute it as code, so the echo function (which would be C++'s equvilant of printf()) would print: '2' to the screen.

Now before you get all excited about this, C++ doesn't support the eval() function.


I realy need such a function to complete my objective. And since there's nothing like this flying around the internets I'm going to code it myself

Does anyone have any experience with marco-languages and custom scripting? I alreay have a few basic ideas. But I've stumbled on a problem. How do I link strings to variable names?
Suppose I have a program like this:

int i = 0;
string str = "i = 2";
eval(str);

How do I make the i in the string refer to the i in the program?
Is this even possible?

-SCHiM

[doofbla]

I haven't tried but isn't this automaticly? you declared i before and if eval() really just executes the string it should work. Or am i totaly false?

[.::SCHiM::.]

I haven't tried but isn't this automaticly? you declared i before and if eval() really just executes the string it should work. Or am i totaly false?

Read the whole post doofbla ;P eval() doesn't exist in C++, so that function is just to illustrate how I'd want to eval() fucnction to work in C++

[doofbla]

Aaaa okay now it's clear for me that i was totaly wrong with my answer

but anyhow i didn't get 100% what you want.

EDIT:
ok you want to code "eval" by yourself but you have to know how to link the string i with the int i?
If yes I'm sorry I don't have a answer & I can't think about a way to do this But maybe others can =)

[zeco]

Hmm sadly I don't think this is possible. . . Well I tried to do some research on the matter and I came up with nothing but people saying various reasons why it would not work because of the paradigms C++ uses as a language.

Though good luck! This would definitely be interesting if you figure out a way.

[Auxilium]

if
i = 1
i+i=2

[php]printf("2");[/php]

[freedompeace]

1. Get input from user.
2. Split string using mathematical deliminators (+, -, =, *, /).
3. Convert each number into a unit (using atoi or a similar function)
4. Apply your mathematical operations
5. Output result.

[.::SCHiM::.]

1. Get input from user.
2. Split string using mathematical deliminators (+, -, =, *, /).
3. Convert each number into a unit (using atoi or a similar function)
4. Apply your mathematical operations
5. Output result.

I already have a skeleton that does that. But the problem with the symbols isn't solved, though I've a few ideas (from the printf statement)

[freedompeace]

I already have a skeleton that does that. But the problem with the symbols isn't solved, though I've a few ideas (from the printf statement)

Lol skeleton.

Anyway, what problem with the symbols?

[.::SCHiM::.]

Lol skeleton.

Anyway, what problem with the symbols?

I cannot get "x = i" the string 'x' to equal the real int x.
That's the only problem left...

[why06]

I cannot get "x = i" the string 'x' to equal the real int x.
That's the only problem left...

I don't think even this will hide your string. Not to mention it seems really hard unless your damn good at macros. If you don't want people to see the string the string then the best option is to not include it in the program.

Do something like calculate the checksum of the string then store that in your program and calculate the checksum of the entered string on the fly. If the two match you have a correct answer.

[.::SCHiM::.]

I don't think even this will hide your string. Not to mention it seems really hard unless your damn good at macros. If you don't want people to see the string the string then the best option is to not include it in the program.

Do something like calculate the checksum of the string then store that in your program and calculate the checksum of the entered string on the fly. If the two match you have a correct answer.

No, that's not what I'm trying to do here... I'm trying to make it possible for C++ to selfmodify itself on the fly. That modification taking place in strings/code or otherwise. If I can get this done...

But it seems that my task is impossible (many others have failed where I will fail aswell)

[doofbla]

I know that "good" spyware changes their code everytime they make a new copy of themself so maybe you should go a bit in that way to get information
(i hope you don't want to make such a tool)


EDIT: i just remembered the name :

POLYMORPHIC VIRUS/SPY-/MALEWARE or whatever...

just google "Polymorphism c++" and you'll find a lot of introductions and tutorials

[why06]

No, that's not what I'm trying to do here... I'm trying to make it possible for C++ to selfmodify itself on the fly. That modification taking place in strings/code or otherwise. If I can get this done...

But it seems that my task is impossible (many others have failed where I will fail aswell)

First off. If your going for polymorphism I would implement it at the asm level, by taking certain instructions and changing them for equivalent instructions or instructions.

Secondly those people who failed were master virus programmers in many cases. A polymorphic self replicating virus seems a little out of your range. Why not try something simpler. Creating polymorphic code is possible, by changing inserting junkbytes in the code, but to actually change the executing instructions themselves is gonna take a lot of work.

[.::SCHiM::.]

First off. If your going for polymorphism I would implement it at the asm level, by taking certain instructions and changing them for equivalent instructions or instructions.

Secondly those people who failed were master virus programmers in many cases. A polymorphic self replicating virus seems a little out of your range. Why not try something simpler. Creating polymorphic code is possible, by changing inserting junkbytes in the code, but to actually change the executing instructions themselves is gonna take a lot of work.

To tell you guys the truth, I was fasinated by the idea of self-modifying code when I first started off writing code. And I never realy lost that fascination.
Although the technique is often used by polymorpic/ metamorphic viruses, and therefore seen as shady, if not mallicious. I think it can be used to create inreverceable exectutables (or atleast take the revercing of such .exe's to a whole new level)

@why

Dang, I knew it was comming for me...
*is of to learn asm, with an determination that will soon probably turn to dread by asm's daunting syntax*

@doofbla

The tutorials you're reffering to are about polymorphism in C++, which is different from writing self-modifying code