Related
Regardless of the language I'm always puzzled by the concept of security through an if. All the code I write relies on success of that one line with if statement:
user = getUserName();
password = getPassword();
if (match(user, password)) {
print secret information;
}
Since it's only one line I feel like sabotage can be relatively simple. Am I overlooking things, or is a single if really the best way to do this?
You are right, an if like this is easily hacked. If one reverse engineers this application, you can easily modify a few instructions to skip the if.
There are various options, like obfuscating the executable or adding more complex checks and in add them in various places in your application. But whatever you do, your application can always be hacked.
Best thing is not to worry about it. By the time your application is so good and great and widely used that people are actually willing to put effort in cracking it, you will probably make enough money to protect it better. Until then, it's a waste of time to even think about it.
In the specific case you are showing, if you were really worried about unauthorized people seeing the secret information output by "print secret information;" you would encrypt the "secret information" with the supplied password. This would ensure that only the person who was able to provide the proper password would be able to see the secret information.
There's one thing about IF's that is often overlooked. It's called timing attack. Suppose you have a web application that does comparison based on direct matching of password sent against password stored in the DB (yes, I know that nobody in his mind will store passwords in the DB, but as Cheshire Cat said, "we are all mad here"). Then comparison procedure takes different time depending on whether the passwords don't match on the first character, on the second one or on the last one. While it might seem that the time difference is tiny, it's enough for attacker to attempt to guess the password even across internet, not talking about local analysis. Timing attack is a bit more complicated, than I described, but in general IF comparison is not 100% safe, at least not in all cases.
The if statement is absolutely secure, and can never be the cause of a vulnerability. Vulnerabilities arise from nearly everything else in your code.
It is possible that the comparison operator that you are using is flawed. For instance the == operator employs fuzzing matching where a range of possible values are accepted. This might not be good for secuirty but its hard to come up with a good example, it doesn't really matter for a password. A simple $password==$_GET['password'] should work just fine.
Your if statement could also be relying on bad regular expression such as
if(preg_match('/(.+)\\.js/'.$_GET['file'])){
readfile($_GET['file']);
}
In this case the regex is looking for a .js anywhere in the string, not enforcing it to be at the end.
?file=../../.js/../../../../../../../etc/passwd
(And this vulnerability won me $3,000 in the Mozilla bug bounty program ;)
If this is a server code - this is not a problem, as long as you keep your server secure.
If this is a client code - you are right. Someone can manipulate your code - either the binary file or the memory image (once loaded). However, this is true for any client application. You can only make it harder (by using tools like PECompact + Anti-debug plugin for example), but you can't achieve very strong security.
I'm not sure to understand your question.
Software security techniques are imperfect, and AFAIK they pre-suppose few bugs in the compiler, and a "perfect" hardware (that is, the processor is interpreting correctly the machine code).
I am not familiar (but interested) with approaches for imperfect hardware (except of course by using redundancy or other techniques, e.g. ECC, to detect hardware errors).
There is nothing insecure about one line with an if in it.
If the code is running on your server, what matters is how secure that server is. If an hacker gains access to it, it doesn't matter how complicated your code is, he will be able to circumvent it.
Similarly, if your code runs on the computer of a potential attacker (like a computer game that you want to protect), there is nothing you can do to stop the attacker. You can make his work slightly more difficult, but that's all.
You shouldn't worry about the security of one line, but of the system as a whole. If you make your code more complicated, all you did is introduce more potential for bugs. Using more complicated code is an attempt at security through obscurity, which doesn't work.
If you can't trust your computer to execute a simple if correctly, you can't trust it at all.
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 8 years ago.
Improve this question
I am currently working on a project where i need to create some architecture, framework or any standards by which i can "at least" increase the cracking method for a software, i.e, to add to software security. There are already different ways to activate a software which includes online activation, keys etc. I am currently studying few research papers as well. But there are still lot of things that i want to discuss.
Could someone guide me to some decent forum, mailing list or something like that? or any other help would be appreciated.
I'll tell you the closest thing to "crackproof": a web application.
Desktop applications are doomed, for many other reasons, but making your application run "in the cloud", in a browser, gives you a lot more control about security.
A desktop software runs on the client's computer, so the client has full access to it. A web app runs on your server, so the client only sees a tiny bit of it.
You need to begin by infiltrating the local hacking gang, posing as an 11 year old who wants to "hack it up". Once you've earned their trust you can learn what features they find hardest to crack. As you secretly release "uncrackable" software to the local message boards, you can see what they do with it. Build upon your inner knowledge until they can no longer crack your software. When that is done, let your identity be known. Ideally, this will be seen as a sign of betrayal, that you're working against them. Hopefully this will lead them to contact other hackers outside the local community to attack your software.
Continue until you've reached the top of the hacker mafia. Write your thesis as a book, sell to HBO.
Isn't it a sign of success when your product gets cracked? :)
Seriously though - one approach is to use License objects that are serialized to XML and then encrypted using public/private key pairs. They are then read back in at runtime, de-serialized and processed to ensure they are valid.
But there is still the ubiquitous "IsValid()" method which can be cracked to always return true.
You could even put that method into a signed assembly to prevent tampering, but all you've done then is create another layer of "IsValid()" which too can be cracked.
We use licenses to turn on or off various features in our software, and to validate support/upgrade periods. But this is only for our legitimate customers. Anyone who wants to bypass it probably could.
We trust our legitimate customers to not try to bypass the licensing, and we accept that our illegitimate customers will find a way.
We would waste more money attempting to imporve the 'tamper proof' nature of our solution that we loose to people who pirate software.
Plus you've got to consider the pain to our legitimate customers, and asking them to paste a license string from their online account page is as much pain as I'd want to put them through. Why create additional barriers to entry for potential customers?
Anyway, depending on which solution you've got in place already, my description above might give you some ideas that might decrease the likelyhood someone will crack your product.
As nute said, any code you release to a customer's machine is crackable.
Don't try for "uncrackable." Try for "there's enough deterrent to reasonably protect my assets."
There are a lot of ways you can try and increase the cost of cracking. Most of them cost you but there is one thing you can do that actually reduces your costs while increasing the cost of cracking: deliver often.
There is a finite cost to cracking any given binary. That cost is increased by the number of binaries being cracked. If you release new functionality every week, you essentially bifurcate your users into two groups:
Those who don't need the latest features and can wait for a crack.
Those who do need the latest features and will pay for your software.
By engaging in the traditional anti-cracking techniques, you can multiply the cost of cracking one binary an, consequently, widen the gap between when a new feature is released and when it is available on the black market. To top it all off, your costs will go down and the amount of value you deliver in a period of time will go up - that's what makes it free.
The more often you release, the more you will find that quality and value go up, cost goes down, and the less likely people will be to steal your software.
As others have mentioned, once you release the bits to users you have given up control of them. A dedicated hacker can change the code to do whatever they want. If you want something that is closer to crack-proof, don't release the bits to users. Keep it on the server. Provide access to the application through the Internet or, if the user needs a desktop client, keep critical bits on the server and provide access to them via web services.
Like others have said, there is no way of creating a complete crack-proof software, but there are ways to make cracking the software more difficult; most of these techniques are actually used by bad guys to hide the malware inside binaries and by game companies to make cracking and copying the games more difficult.
If you are really serious about doing this, you could check e.g., what executable packers like UPX do. But then you need to implement the unpacker also. I do not actually recommend doing this, but studying game protectors and binary obfuscation might help you in your quest.
First of all, in what language are you writing this?
It's true that a crack-proof program is impossible to achieve, but you can always make it harder. A naive approach to application security means that a program can be cracked in minutes. Some tips:
If you're deploying to a virtual machine, that's too bad. There aren't many alternatives there. All popular vms (java, clr, etc.) are very simple to decompile, and no obfuscator nor signature is enough.
Try to decouple as much as possible the UI programming with the underlying program. This is also a great design principle, and will make the cracker's job harder from the GUI (e.g. enter your serial window) to track the code where you actually perform the check
If you're compiling to actual native machine code, you can always set the build as a release (not to include any debug information is crucial), with optimization as high as possible. Also in the critical parts of your application (e.g. when you validate the software), be sure to make it an inline function call, so you don't end up with a single point of failure. And call this function from many different places in your app.
As it was said before, packers always add up another layer of protection. And while there are many reliable choices now, you can end up being identified as a false positive virus by some anti-virus programs, and all the famous choices (e.g. UPX) have already pretty straight-forward unpackers.
there are some anti-debugging tricks you can also look for. But this is a hassle for you, because at some time you might also need to debug the release application!
Keep in mind that your priority is to make the critical part of your code as untraceable as possible. Clear-text strings, library calls, gui elements, etc... They are all points where an attacker may use to trace the critical parts of your code.
I need to write a small program that can detect that it has been changed. Please give me a suggestion!
Thank you.
The short answer is to create a hash or key of the program and have the program encrypt and store that key within itself. From time to time the program would make a checksum of itself and compare it against that hash/key. If there is a difference then handle it accordingly.
There are lots and lots of ways to go about this. There are lots of very smart engineers out there that know how to work around it if that is what you are trying to avoid.
The simplest way would be to use a hash function to generate a short code which is a digest of the whole program and then check this.
It would be fairly easy to debug the code and replace the hash value to subvert this.
A better way would be to generate a digital signature using your private key and with the public key in the program to check it.
This would then require changing the public key and the hash as well as understanding the program, or changing the program code itself to subvert the check.
All you can do in the case described so far is make it more difficult to subvert but it will be possible with a certain amount of effort. I'd suggest looking into cryptographic techniques and copy protection for more information to suit your specific case.
Do you mean that program 'foo' should be able to tell if some part of it was modified prior to / during run time? That's not the responsibility of the program, its the responsibility of the security hooks in the target OS.
For instance, if the installed and trusted 'foo' has signature "xyz1234" , the kernel should refuse to run a modified (or completely new) 'foo'. The same goes for 'foo' while its currently running in memory. Look up 'Trusted Path Of Execution', aka TPE to start.
A better question to ask would be how to sign your released version of 'foo', which depends upon your target platform.
try searching for "code signing"
The easiest way would be for the program to detect its own md5 and store that in a separate file, but this isn't totally secure. An MD5 + CRC might work slightly better.
Or as others here have suggested, a sha1, sha2 or sha3 which are much more secure than md5 currently.
I'd ask an external tool to do the check. This problem reminds me of the challenge to write a program that prints itself. In Bash you could do something like this:
#!/bin/bash
cat $0
which really asks for an external tool to do the job. It's kind of solving the problem by getting away from solving the problem...
The best option is going to be code signing -- either using a tool supplied by your local friendly OS (For example, If you're targeting Windows, you probably want to take a look at Authenticode where the Operating System handles the tampering), or by rolling your own option storing MD5 hashes and comparing
It is important to remember that bets are off if someone injects a thread into your process (to potentially kill your ongoing checks, etc.), or if they tamper with your compiled application to bypass said checks.
An alternative way which wasn't mentioned is to use a binary packer such as UPX.
If the binary gets changed on the disk then the unpacking code is likely to fail.
This however doesn't protect you if someone changes the binary while it is in memory.
Anyone visiting a torrent tracker is sure to find droves of "cracked" programs ranging from simple shareware to software suites costing thousands of dollars. It seems that as long as the program does not rely on a remote service (e.g. an MMORPG) that any built-in copy protection or user authentication is useless.
Is it effectively not possible to prevent a cracker from circumventing the copy protection? Why?
No, it's not really possible to prevent it. You can make it extremely difficult - some Starforce versions apparently accomplished that, at the expense of seriously pissing off a number of "users" (victims might be more accurate).
Your code is running on their system and they can do whatever they want with it. Attach a debugger, modify memory, whatever. That's just how it is.
Spore appears to be an elegant example of where draconian efforts in this direction have not only totally failed to prevent it from being shared around P2P networks etc, but has significantly harmed the image of the product and almost certainly the sales.
Also worth noting that users may need to crack copy protection for their own use; I recall playing Diablo on my laptop some years back, which had no internal optical drive. So I dropped in a no-cd crack, and was then entertained for several hours on a long plane flight. Forcing that kind of check, and hence users to work around it is a misfeature of the stupidest kind.
It is impossible to stop it without breaking your product. The proof:
Given: The people you are trying to prevent from hacking/stealing will inevitably be much more technically sophisticated than a large portion of your market.
Given: Your product will be used by some members of the public.
Given: Using your product requires access to it's data on some level.
Therefore, You have to released you encrypt-key/copy protection method/program data to the public in enough of a fashion that the data has been seen in it's useable/unencrypted form.
Therefore, you have in some fashion made your data accessible to pirates.
Therefore, your data will be more easily accessible to the hackers than your legitimate audience.
Therefore, ANYTHING past the most simplistic protection method will end up treating your legitimate audience like pirates and alienating them
Or in short, the way the end user sees it:
Because it's a fixed defense against a thinking opponent.
The military theorists beat this one to death how many millennia ago ?
Copy-protection is like security -- it's impossible to achieve 100% perfection but you can add layers that make it successively more difficult to crack.
Most applications have some point where they ask (themselves), "Is the license valid?" The hacker just needs to find that point and alter the compiled code to return "yes." Alternatively, crackers can use brute-force to try different license keys until one works. There's also social factors -- once one person buys the tool they might post a valid license code on the Internet.
So, code obfuscation makes it more difficult (but not impossible) to find the code to alter. Digital signing of the binaries makes it more difficult to change the code, but still not impossible. Brute-force methods can be combated with long license codes with lots of error-correction bits. Social attacks can be mitigated by requiring a name, email, and phone number that is part of the license code itself. I've used that method to great effect.
Good luck!
Sorry to bust in on an ancient thread, but this is what we do for a living and we're really really good at it. It's all we do. So some of the information here is wrong and I want to set the record straight.
Theoretically uncrackable protection is not only possible it's what we sell. The basic model the major copy protection vendors (including us) follow is to use encryption of the exe and dlls and a secret key to decrypt at runtime.
There are three components:
Very strong encryption: we use AES 128-bit encryption which is effectively immune to a brute force attack. Some day when quantum computers are common it might be possible to break it but it's unreasonable to assume you will crack this strength encryption to copy software as opposed to national secrets.
Secure key storage: if a cracker can get the key to the encryption, you're hosed. The only way to GUARANTEE a key can't be stolen is to store it on a secure device. We use a dongle (it comes in many flavors but the OS always just sees it as a removable flash drive). The dongle stores the key on a smart card chip which is hardened against side channel attacks like DPA. The key generation is tied to multiple factors which are non-deterministic and dynamic so no single key/master crack is possible. The communication between the key storage and the runtime on the computer is also encrypted so a man-in-the-middle attack is thwarted.
Debugger detection: Basically you want to stop a cracker from taking a snapshot of memory (after decryption) and making an executable out of that. Some of the stuff we do to prevent this is secret, but in general we allow for debugger detection and lock the license when a debugger is present (this is an optional setting). We also never completely decrypt the entire program in memory so you can never get all the code by "stealing" memory.
We have a full time cryptologist who can crack just about anybody's protection system. He spends all his time studying how to crack software so we can prevent it. So you don't think this is just a cheap shill for what we do, we're not unique: other companies such as SafeNet and Arxan Technologies can do some very strong protection as well.
A lot of software-only or obfuscation schemes are easy to crack since the cracker can just identify the program entry point and branch around any any license checking or other stuff the ISV has put in to try to prevent piracy. Some people even with dongles will throw up a dialog when the license isn't found--setting a breakpoint on that error will give the cracker a nice place in the assembly code to do a patch. Again, this requires unencrypted machine code to be available--something you don't get if you do strong encryption of the .exe.
One last thing: I think we're unique in that we've had several open contests where we provided a system to people and invited them to crack it. We've had some pretty hefty cash prizes but no one has yet cracked our system. If an ISV takes our system and implements it incorrectly it's no different from putting a great padlock on your front door attached to a cheap hasp with wood screws--easy to circumvent. But if you use our tools as we suggest we believe your software cannot be cracked.
HTH.
The difference between security and copy-protection is that with security, you are protecting an asset from an attacker while allowing access by an authorized user. With copy protection, the attacker and the authorized user are the same person. That makes perfect copy protection impossible.
I think given enough time a would-be cracker can circumvent any copy-protection, even ones using callbacks to remote servers. All it takes is redirecting all outgoing traffic through a box that will filter those requests, and respond with the appropriate messages.
On a long enough timeline, the survival rate of copy protection systems is 0. Everything is reverse-engineerable with enough time and knowledge.
Perhaps you should focus on ways of making your software be more attractive with real, registered, uncracked versions. Superior customer service, perks for registration, etc. reward legitimate users.
Basically history has shown us the most you can buy with copy protection is a little time. Fundamentally since there is data you want someone to see one way, there is a way to get to that data. Since there is a way someone can exploit that way to get to the data.
The only thing that any copy protection or encryption for that matter can do is make it very hard to get at something. If someone is motivated enough there is always the brute force way of getting around things.
But more importantly, in the computer software space we have tons of tools that let us see how things are working, and once you get the method of how the copy protection works then its a very simple matter to get what you want.
The other issue is that copy protection for the most part just frustrates your users who are paying for your software. Take a look at the open source model they don't bother and some folks are making a ton of money encouraging people to copy their software.
"Trying to make bits uncopyable is like trying to make water not wet." -- Bruce Schneier
Copy protection and other forms of digital restrictions management are inherently breakable, because it is not possible to make a stream of bits visible to a computer while simultaneously preventing that computer from copying them. It just can't be done.
As others have pointed out, copy protection only serves to punish legitimate customers. I have no desire to play Spore, but if I did, I'd likely buy it but then install the cracked version because it's actually a better product for its lack of the system-damaging SecuROM or property-depriving activation scheme.
}} Why?
You can buy the most expensive safe in the world, and use it to to protect something. Once you give away the combination to open the safe, you have lost your security.
The same is true for software, if you want people to use your product you must given them the ability to open the proverbial safe and access the contents, obfuscating the method to open the lock doesn't help. You have granted them the ability to open it.
You can either trust your customers/users, or you can waste inordinate amounts of time and resource trying to defeat them instead of providing the features they want to pay for.
It just doesn't pay to bother. Really. If you don't protect your software, and it's good, undoubtedly someone will pirate it. The barrier will be low, of course. But the time you save from not bothering will be time you can invest in your product, marketing, customer relationships, etc., building your customer base for the long term.
If you do spend the time on protecting your product instead of developing it, you'll definitely reduce piracy. But now your competitors may be able to develop features that you didn't have time for, and you may very well end up selling less, even in the short term.
As others point out, you can easily end up frustrating real and legitimate users more than you frustrate the crooks. Always keep your paying users in mind when you develop a circumvention technique.
If your software is wanted, you have no hope against the army of bored 17 year old's. :)
In the case of personal copying/non-commercial copyright infringement, the key factor would appear to be the relationship between the price of the item and the ease of copying it. You can increase the difficulty to copy it, but with diminishing returns as highlighted by some of the previous answers. The other tack to take would be to lower the price until even the effort to download it via bittorrent is more cumbersome than simply buying it.
There are actually many successful examples where an author has found a sweet spot of pricing that has certainly resulted in a large profit for themselves. Trying to chase a 100% unauthorized copy prevention is a lost cause, you only need to get a large group of customers willing to pay instead of downloading illegaly. The very thing that makes pirating softweare inexpensive is also what makes it inexpensive to publish software.
There's an easy way, I'm amazed you haven't said so in the answers above.
Move the copy protection to a secured area (understand your server in your secure lab).
Your server will receive random number from clients (check that the number wasn't used before), encrypt some ever evolving binary code / computation results with clients' number and your private key and send it back.
No hacker can circumvent this since they don't have access to your server code.
What I'm describing is basically webservice other SSL, that's where most company goes nowadays.
Cons: A competitor will develop an offline version of the same featured product during the time you finish your crypto code.
On protections that don't require network:
According to notes floated around it took two years to crack a popular application which used similar scheme as described in John's answer. (custom hardware dongle protection)
Another scheme which doesn't involve a dongle is "expansive protection". I coined this just now, but it works like this: There's an application which saves user data and for which the users can buy expansions and such from 3rd parties. When user loads the data or uses new expansion, the expansions and the saved data contains also code which performs checks. And of course these checks are also protected by checksum checks. It's not as secure on paper as the other scheme but in practise this application has been half-cracked all the time, so that it mostly functions as a trial despite being cracked as the cracks will always miss some checks and have to patch these expansions as well.
The key point is, while these can be cracked, if enough software vendors used such schemes, this would overwork the few people in the warescene who are willing to dedicate themselves to those. If you do the maths, the protections don't have to be even that great, as long as enough vendors used these custom protections that changed constantly, it would simply overwhelm the crackers and the warez scene would end then and there. *
The only reason this hasn't happened is because publishers buy a single protection that they use all over, making it a huge target just like Windows is target for malware, any protection used in more than single app is a bigger target. So everyone needs to be doing their own custom, unique multi-layered expansive protection. The amount of warez releases would drop to maybe dozen releases per year if it takes months to crack a single release by the very best crackers.
Now for some theorycrafting in marketing software:
If you believe that warez provides worthwhile marketing value, then that should be factored in the business plan. This could entail a very very (too) basic lite version that still cost few dollars to ensure it was cracked. Then you'd hook in the users with "limited time upgrade cheaply from the lite version" offers regularly and other upselling tactics. The lite version should really have at most one buy-worthy feature and otherwise be very crippled. The price should probably be <10 $. The full version should probably be twice as much as the upgrade price from the $10 lite pay-demo version. eg. If the full-version is $80, You'd offer upgrades from the lite version to full version for $40 or something that really seems like killer bargain. Of course you'd avoid revealing these bargains to purchasers who went direct for the $80 edition.
It would be critical that the full version shared no similarity in code to the lite version. You'd intend that the lite-version gets warezed and the full-version will either be time intensive to crack or have network dependency in functionality that will be hard to mimic locally. Crackers are probably more specialized in cracking than trying to code up/replicate parts of functionality that the application has on the web server.
* addendum: for apps/games the scene might end in such unlikely and theoretical circumstance, for other things like music/movies and in practise, I'd look at making it cheap for digital dl buyers to get additional collectible physical items or online-only value - many people are collectors of stuff (especially the pirates) and they could be enticed into buying if it gains something desirable enough over just a digital copy.
Beware though - There's something called "the law of rising expectations". Example from games: Ultima 4-6 standard box included a map made of cloth, and Skyrim Collectors edition has a map made of paper. Expectations had risen and some people aren't going to be happy with a paper map. You want to either keep quality of produce or service constant or manage expectations ahead of time. I believe this is critical when considering these value-add things as you want them to be desirably but not increasingly expensive to make and not turn into something that seems so worthless that it defeats the purpose.
This is one occasion where quality software is a bad thing, because if no one whats your software then they will not spend time trying to crack it, on the other hand things like Adobe's Master Collection CS3, were available just days after release.
So the moral of this story is if you don't want someone to steal your software there is one option: don't write anything worth stealing.
I think someone will come up with a dynamic AI way of defeating all the currently standard methods of copy protection; heck, I'd sure love to get paid to work on that problem. Once they get there then new methods will be developed, but it'll slow things down.
The second best way for society to stop theft of software, is to penalize it heavily, and enforce the penalties.
The best way is to reverse the moral decline, and thereby increase the level of integrity in society.
A lost cause if ever I heard one... of course that doesn't mean you shouldn't try.
Personally, I like Penny Arcade's take on it: "A Cyclical Argument With A Literal Strawman"alt text http://sonicloft.net/im/52
My question is pretty straightforward: You are an executable file that outputs "Access granted" or "Access denied" and evil persons try to understand your algorithm or patch your innards in order to make you say "Access granted" all the time.
After this introduction, you might be heavily wondering what I am doing. Is he going to crack Diablo3 once it is out? I can pacify your worries, I am not one of those crackers. My goal are crackmes.
Crackmes can be found on - for example - www.crackmes.de. A Crackme is a little executable that (most of the time) contains a little algorithm to verify a serial and output "Access granted" or "Access denied" depending on the serial. The goal is to make this executable output "Access granted" all the time. The methods you are allowed to use might be restricted by the author - no patching, no disassembling - or involve anything you can do with a binary, objdump and a hex editor. Cracking crackmes is one part of the fun, definately, however, as a programmer, I am wondering how you can create crackmes that are difficult.
Basically, I think the crackme consists of two major parts: a certain serial verification and the surrounding code.
Making the serial verification hard to track just using assembly is very possible, for example, I have the idea to take the serial as an input for a simulated microprocessor that must end up in a certain state in order to get the serial accepted. On the other hand, one might grow cheap and learn more about cryptographically strong ways to secure this part. Thus, making this hard enough to make the attacker try to patch the executable should not be tha
t hard.
However, the more difficult part is securing the binary. Let us assume a perfectly secure serial verification that cannot be reversed somehow (of course I know it can be reversed, in doubt, you rip parts out of the binary you try to crack and throw random serials at it until it accepts). How can we prevent an attacker from just overriding jumps in the binary in order to make our binary accept anything?
I have been searching on this topic a bit, but most results on binary security, self verifying binaries and such things end up in articles that try to prevent attacks on an operating system using compromised binaries. by signing certain binaries and validate those signatures with the kernel.
My thoughts currently consist of:
checking explicit locations in the binary to be jumps.
checksumming parts of the binary and compare checksums computed at runtime with those.
have positive and negative runtime-checks for your functions in the code. With side-effects on the serial verification. :)
Are you able to think of more ways to annoy a possible attacker longer? (of course, you cannot keep him away forever, somewhen, all checks will be broken, unless you managed to break a checksum-generator by being able to embed the correct checksum for a program in the program itself, hehe)
You're getting into "Anti-reversing techniques". And it's an art basically. Worse is that even if you stomp newbies, there are "anti-anti reversing plugins" for olly and IDA Pro that they can download and bypass much of your countermeasures.
Counter measures include debugger detection by trap Debugger APIs, or detecting 'single stepping'. You can insert code that after detecting a debugger breakin, continues to function, but starts acting up at random times much later in the program. It's really a cat and mouse game and the crackers have a significant upper hand.
Check out...
http://www.openrce.org/reference_library/anti_reversing - Some of what's out there.
http://www.amazon.com/Reversing-Secrets-Engineering-Eldad-Eilam/dp/0764574817/ - This book has a really good anti-reversing info and steps through the techniques. Great place to start if you're getting int reversing in general.
I believe these things are generally more trouble than they're worth.
You spend a lot of effort writing code to protect your binary. The bad guys spend less effort cracking it (they're generally more experienced than you) and then release the crack so everyone can bypass your protection. The only people you'll annoy are those honest ones who are inconvenienced by your protection.
Just view piracy as a cost of business - the incremental cost of pirated software is zero if you ensure all support is done only for paying customers.
There's TPM technology: tpm on wikipedia
It allows you to store the cryptographic check sums of a binary on special chip, which could act as one-way verification.
Note: TPM has sort of a bad rap because it could be used for DRM. But to experts in the field, that's sort of unfair, and there's even an open-TPM group allowing linux users control exactly how their TPM chip is used.
One of the strongest solutions to this problem is Trusted Computing. Basically you would encrypt the application and transmit the decryption key to a special chip (the Trusted Platform Module), The chip would only decrypt the application once it has verified that the computer is in a "trusted" state: no memory viewers/editors, no debuggers etc. Basically, you would need special hardware to just be able to view the decrypted program code.
So, you want to write a program that accepts a key at the beginning and stores it in memory, subsequently retrieving it from disc. If it's the correct key, the software works. If it's the wrong key, the software crashes. The goal is that it's hard for pirates to generate a working key, and it's hard to patch the program to work with an unlicensed key.
This can actually be achieved without special hardware. Consider our genetic code. It works based on the physics of this universe. We try to hack it, create drugs, etc., and we fail miserably, usually creating tons of undesirable side-effects, because we haven't yet fully reverse engineered the complex "world" in which the genetic "code" evolved to operate. Basically, if you're running everything on an common processor (a common "world"), which everyone has access to, then it's virtually impossible to write such a secure code, as demonstrated by current software being so easily cracked.
To achieve security in software, you essentially would have to write your own sufficiently complex platform, which others would have to completely and thoroughly reverse engineer in order to modify the behavior of your code without unpredictable side effects. Once your platform is reverse engineered, however, you'd be back to square one.
The catch is, your platform is probably going to run on common hardware, which makes your platform easier to reverse engineer, which in turn makes your code a bit easier to reverse engineer. Of course, that may just mean the bar is raised a bit for the level of complexity required of your platform to be sufficiently difficult to reverse engineer.
What would a sufficiently complex software platform look like? For example, perhaps after every 6 addition operations, the 7th addition returns the result multiplied by PI divided by the square root of the log of the modulus 5 of the difference of the total number of subtract and multiply operations performed since system initialization. The platform would have to keep track of those numbers independently, as would the code itself, in order to decode correct results. So, your code would be written based on knowledge of the complex underlying behavior of a platform you engineered. Yes, it would eat processor cycles, but someone would have to reverse engineer that little surprise behavior and re-engineer it into any new code to have it behave properly. Furthermore, your own code would be difficult to change once written, because it would collapse into irreducible complexity, with each line depending on everything that happened prior. Of course, there would be much more complexity in a sufficiently secure platform, but the point is that someone would have reverse engineer your platform before they could reverse engineer and modify your code, without debilitating side-effects.
Great article on copy protection and protecting the protection Keeping the Pirates at Bay:
Implementing Crack Protection for Spyro: Year of the Dragon
The most interesting idea mentioned in there that hasn't yet been mentioned is cascading failures - you have checksums that modify a single byte that causes another checksum to fail. Eventually one of the checksums causes the system to crash or do something strange. This makes attempts to pirate your program seem unstable and makes the cause occur a long way from the crash.