问题
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?
回答1:
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.
回答2:
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.
回答3:
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:
回答4:
Because it's a fixed defense against a thinking opponent.
The military theorists beat this one to death how many millennia ago ?
回答5:
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!
回答6:
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.
回答7:
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.
回答8:
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.
回答9:
"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.
回答10:
}} 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.
回答11:
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.
回答12:
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. :)
回答13:
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.
回答14:
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.
回答15:
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.
回答16:
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.
回答17:
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.
回答18:
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
来源：https://stackoverflow.com/questions/203229/preventing-copy-protection-circumvention