|Password Recovery Solutions|
(c) 1997 Vitas Ramanchauskas
Please note: this article was written in 1997, it does not cover latest developments!
At one Web site I’ve seen a curious discourse, whether your programs should be furnished with anti-pirate devices. It went like this: No one has a right to enter your house without your consent. The inviolability of your house is protected by law. Nevertheless, you prefer to have a lock in your front door. Further proceeding with this comparison, we’d have to admit that after putting a lock on the door many software authors leave their keys at the front door or they lock a wrong door at all.
Here are some initial remarks.
This article is intended for those software developers who do not professionally engage in issues of protection from any unauthorized usage. It’s aimed at pointing out the most typical mistakes and helping to create more impregnable software.
Discussed here are the issues of creation of shareware and trial versions for Windows’95 (and Windows NT, if stated so). Leaving specific examples aside we can say that everything that is mentioned below is true for other platforms, too.
This article does not claim to cover the problem in its entirety.
You can contact the author at firstname.lastname@example.org. Even if you don’t have any specific suggestions or notices just send in your opinions about this article. This article may be continued in future, so please give us your opinion about this, too.
There exists an opinion that hackers are unique specialists and they can be fought only by specialists like them, yet an ordinary software developer is unable to do it and he shouldn’t even try to. Therefore you shouldn’t try to protect a program from a break-in, because it wouldn’t save from a hacker and you should only create a simple fool-proof protection. Meanwhile, as unexpected as it may sound, a typical hacker is not in any way an able specialist; he cracks programs because he is unable to do anything else (a proverb «It’s easier to break than to build» is true to life!). If you weren’t seriously into illegal copy protection (don’t waste your time if you were – in this case, this article is not intended for you) then you are going to discover a number a number of simple, logical and very efficient ways of increasing your programs’ reliability upon reading this article (at least, I hope so). Well, of course, there are skilled professionals among hackers, and they could do a lot. The methods which are described here would not stop them. Nevertheless, if reading this article helps you to improve your program in a few hours well enough to repel a lot of pitiful hackers – it is not so bad, is it?
There are two big problems concerning unauthorized copy protection of shareware programs. The first one is how to prevent a hacker from turning a shareware version into a complete registered one. The second one is a copy protection of a registered program, that is how to arrange that only the legal owner could use a registered copy. This second problem is going to be touched upon in the end of this article as it requires a greater separate discussion.
Ways to create a shareware product.
When offering a shareware version of his program an author pursues two goals. On one hand, he wants to get a potential user interested therefore a program should demonstrate all of its options and be as convenient as possible. On the other hand he wants to make a user pay for the program. The folowing methods are the most popular ones for creating shareware programs.
A demo program.
A potential user is receiving an «inferior» program with some options completely missing, Having tried it, he’s buying a normal version in a usual way. The determining fact here is that there is no way even in theory to turn a demo version into a complete program. I’m mentioning this choice here, yet I’m not going to discuss it. Sometimes demo versions are made via introduction of some limitations in a complete version whereas a theoretical possibility to do away with these limitations remains. Let’s have a look at two examples. A phone directory demo version contains phone numbers from just one phone station. No hacker can ever turn this demo program to a full-scale phone directory. Another example is a demo version of a graphics editor, which won’t allow you to open images greater than any predefined size. It is very probable that a hacker may quickly remove this limitation. The difference between these two examples is that a phone directory has a part which is totally missing from it. On the contrary, in the second example there is a removable «extra part».
A shareware version does not include some useful functions which only appear after the registration. It’s very important to determine what functions are going to be inaccessible during the trial period. At the present time the software market is extremely satiated. For most of the programs there exists an alternative by a competitor. So, if you deprive a user of many useful functions he may not want to try your program any further and buy it. It is well known that, when meeting a new person, one’s attitude to him (or her) is formed during the very first seconds of the acquaintance. The same thing happens to items and programs – it is very important that your program impresses a user as much as possible. Therefore, the missing functions must be useful but not essential for the first acquaintance with the program. Moreover, these functions must be evident and intuitive, that is, a user should clearly see what exactly is going to be at his disposal after the registration and how convenient his work is going to be. During the trial period a user should get used to your program, get familiar with it and want to use its at its full power and at any time. Therefore a choice of options to be removed for the trial period is very important.
Date of usage and launch count limitations.
It’s a very popular method of protection. It does not have a drawback of a previous method – as soon as at a time of trial your program is going to be presented at its best for the user. This method is accepted in beta versions of many programs to limit the time of their usage (testing). Even the well-known Microsoft corp. uses this way of testing.
During the trial period a program does something to annoy a user but not to prevent the usage of all options of the program. Usually it is a reminder about a necessity of the registration. A good example is a popular WinZip program which recommends to register itself after every launch. This variant differs from the first one by the necessity to «add» something in case #1 and the necessity to «remove» something in case #3. It is evident that the third method is outperformed from the point of view of reliability.
This option is intended for honest people – a program would just inform them that it is not registered yet or who it is registered for (on-screen, in a demo or in an About box). This way of protection is present almost in any program, but usually it is not the only one.
A new version of a program should allow using itself only if a previous version of this program is already installed.
How a program is being registered? Of course there
exists an option that, upon paying for the program, a user will receive a
new (or complete) version in a glossy box bundled with complete
documentation, possibly delivered by a parcel service. In this case we’ll
have to speak about a demo program which is followed by a purchase of a
complete version, yet we have decided not to discuss this case. Another
drawback of this method is that a user does not receive a result
immediately following a money transaction (for example, paying on-line
with a credit card), having to wait for it several days (at best).
Moreover, an Internet program distribution without traditional boxes,
floppies and manuals allows to cut expenses down and to increase
efficiency, which is so important for various utilities and other
inexpensive programs. Upon a registration a user is naturally supposed to
receive something that can turn a program into a registered one from a
program manufacturer. Usually this something is a registration number, but
let us understand it widely – it does not have to be a number, it is a
piece of information given to a user by a program distributor. Given a
chance, you should make this number readable and not too long. Consider,
for example, entering such a registration code:
04846718351B3E6B3D717E240A200A29556B7C18347A1162526F5C This real-life
example (well, maybe almost real-life :-) ) is a registration number from
a program named GoldEd. You should make it more readable, that is, use
only digits and separate groups of digits with optional separators, like
Ways of cracking and ways of protection.
Most of shareware programs can be cracked so easily mostly because their authors cannot imagine what methods are use by hackers for cracking. Below we are going to discuss the simplest and the most frequently used ways of program cracking and ways of protection.
Cracking programs with date limitation or launch count limitation.
In case of limitations that are imposed on period of program usage or times a program had been launched some specific cracking methods become available not only for hacker, but for smart users, too. One of the ways to cheat a protection goes like this: before installing the program it is necessary to set a date several years ahead, for example, at 12.31.2017. Let’s say your program only works during two weeks after having been installed. Then it’s protection system would decide the program is supposed to work till 01.14.2018. Having installed the program, a user reverts to a correct date and uses your program till the end of the world. How could one counter such a method?
The first palliative is to check a current date and, if it is too big (say, more than six months since program release), suggest to use a newer version. A more radical way is to check a current date every time a program is being launched. If, suddenly, it turns out that a current date is lesser than the installation date, then… At this point you may be tempted to display a message which accuses the user of cheating and maybe even to uninstall a program. DON’T DO IT! The user’s system might just have a time failure. Alas, if a time failure did happen, your program will stop working short of its time. This is a rule of thumb – increasing protection reliability leads to increasing your program’s discrimination. A program can be made to behave a bit smarter – if system time is lesser than the program release time then the system clock has really failed, because when a failure occurs a date is often set to 1.1.1980. In this case you can suggest a user to correct the system clock.
The second way of cracking lies in setting a wrong date at the runtime and restoring a correct date afterwards. Of course, this way is a bit awkward, but, unfortunately, there are programs which help to automate this process. It is extremely hard to counter this method. You can try the following ways to do it.
It is a radical way which can be afforded only by developers of Internet-based programs. Since a user is supposed to work online, your program can get a current date and time from a server that provides with exact time and date; there is quite a lot of them now. At the same time your program can do a good service by synchronizing the system’s time and date if they are set incorrectly.
Unfortunately, this way is acceptable for very few programs. It can be slightly modified; if a computer works in a local network, a date can be obtained from a server or from other computers.
If this way is unacceptable, either, we have to admit that without leaving the bounds of a computer, there is no way your program can find out what date it is. Yet, a fact of altering a date still can be detected. Many programs, for example, record their relevant information into the Registry. For this reason, the registry modification date usually matches the current date. When Windows is started, the system creates backup copies for the files c:\windows\system.da0 and c:\windows\user.da0 (these files are marked as the hidden ones).
You can check the date of their last modification and, if it turns out to be greater than the current one, then a user must have set the clock to an earlier date. It is important to check the backup Registry files because the current registry files may already have been modified and therefore their modification date may match the current wrong date. Evidently you can not only check the Registry files like this, you can also verify your own data files. Here’s how a real current date may be obtained: as you may or may not know, Windows’ 95 not only stores the creation date/time for each file, it also stores the time and date of its last access. As a true current date you can consider the last access time of a file which is always launched or opened once when Windows start up. Autoexec.bat or windows\system\vmm32.vxd may serve as examples of such files.
The third and the last way of protection that we are going to consider consists of installation and uninstallation of a program. Modern programs usually have convenient setup utilities which install and deinstall programs. As a result, it may be not burdensome at all to perform a simple installation procedure once a month. There are different methods to fight this method. If, for example, your program requires a great deal of setting its options, you can arrange it in such way that uninstalling a program would cause all options to be lost and a program would have to be set up again after the repetitive installations. A more radical solution would be to leave a mark in a computer (in a Registry, for example) which would state that a program had already been used on this computer and to refuse to install a program if such a mark exists. Indeed, your program would have to be a true perfection so that a user would want to reinstall Windows just to be able to use it. Should I mention that this mark must not be removed by an uninstaller, it should not be located close to other settings of your program and the last, but not the least: use your imagination! If your program is named CoolApp.exe, do not name the register key for its mark as CoolAppWasHere! An alternative of using the Registry may be a small DLL in the Windows directory which an uninstaller does not remove.
If there is a limitation of a launch count, then a counter must be decremented after each launch. (It may be incremented – this is totally irrelevant for us. Let’s suppose it is decremented, just to be certain.) It is very probable that this counter is located in the Registry or in an ini.-file. At times, it’s just amazing to see how clever people who are able to create brilliant programs show miraculous narrow-mindedness and name this counter, for example, iTimeSpan, like it is named in the FineReader program. Name this key variable, for instance, RAS32stub and make its value equal to the remaining launches count with a checksum, encrypted in any code, even a trite XOR. Although this may not help you a great deal – if a hacker finds the counter, he can just restore its original value every time. A radical remedy which is acceptable for Internet-based applications is keeping your counter on a server instead of a local computer.
It is possible to store into a parameter a checksum of the remaining parameters, including the counter itself. In this case all the settings of the program can only be restored together.
You can try and hide the counter outside the Registry, because this location is too evident. You can come up with an impressive name for an .INI file (which, by the way, may have an extension other than «INI.»), stuff this file with a load of settings with intimidatingly complex names (the counter is to be one of them), place it in the Windows directory, and, more importantly, every time you decrement the counter, you should forcefully set the same date for this file, 08.24.95, for instance. I hope you have been already influenced by the anti-hacker spirit and understand, why I’m suggesting you to use this date.
Comparing the time-of-usage and launch-count limitations we’ll have to admit that the second option is less reliable because of the necessity to keep a constantly changing counter which can be found with relative ease.
Methods of hacking without code modification.
Suppose a registration process involves sending a registration number as a response to a user name. All too often, just after a program is released a key generating program appears. Such a program is able to generate a registration number for any given user name. Meanwhile, it is not hard to arrange everything in such way that creation of key-generating programs would be completely impossible. To accomplish this, it would be sufficient for you to use a simple asymmetrical encryption algorithm. You can find a lot of information about asymmetrical encryption algorithms, often dubbed as open-key systems, for example, at www.rsa.com. To put it in a nutshell, asymmetrical encryption algorithm is a way of coding information which requires one key for the encryption and another one for the decryption, yet it is impossible to obtain both of the keys, knowing just one of them. As a rule one of the keys is made as an «open» one (which one of them it is depends on the purpose of their usage), that is, a commonly known key, the other one is kept as a secret. Now consider this: a registration number is a user name which is encrypted with an asymmetrical encryption algorithm, and the encryption password (a key, that is) is known only by you. A program would perform the verification by decrypting the registration number (the decryption key is built into the program) and comparing the result with the user name. If such an algorithm is used correctly, it is totally impossible to create a key generating program. It has to be noticed, however, that the aforementioned way of protection will not prevent from using someone else’s key and from cracking by modification of program code. This method is essentially an electronic signature with a registered under name by the program’s author.
Most of modern commercial (non-shareware) programs require entering a serial number during the registration. This would pose no problem for a legal user – the number can be found in the program package, and could pose a problem for an illegal one (if we aren’t talking about a pirated CD, that is, because thoughtful pirates often place a file with a required serial number on the same disk). A serial number has to satisfy several criterias therefore a random number will not work. Yet all too often an implementation of checking the number validity cannot stand any criticism. For example, most of Microsoft products can be satisfied with a number which consists only of 1’s. Here’s a method of verification which can be advised (actually, there can be quite a lot of options): the first part of the serial number is encrypted (even in the most primitive way), the result checksum is calculated and then a remainder of division of checksum by some number X is calculated. The resulting remainder should match the second part of the checksum. No matter what kind of verification you use, at least it should not miss banal numbers like all zeros or all 1’s. It would be a good idea to provide a link between a serial number and a program name and/or version to make it impossible to use serial numbers from one of your programs with another one. One quite successful brand of this method of protection is a method which requires entering word # N from page # M from printed manual which should be provided with the program in this case.
Here’s a bit about upgrades. A newer version of a program which allows to be used only if there is a previous version of this program already installed on the computer must have some mechanics that scans for the previous version. In a likely way Windows-95’ upgrade requires presence of Windows 3.1 during the installation. Yet, alas, all of the verification consists of checking for presence of a file windows\system\win386.exe. It is enough to create a file with this name (you can even make it 0 bytes long) and Windows ’95 can be installed on a computer where there is no and has never been Windows 3.1 present. Hence the verification should be a bit more complex. For example, an upgrade version of a program may purposefully omit setting several options in the Registry, provided they match those in the previous version. It is possible to come up with a lot more of highly reliable methods.
Methods of hacking involving code modification. Very often hackers turn a shareware program into a full-scale working one, having changed just one byte in its code and having spent just a few minutes. How do they do it? How do they manage to find a right place in a multi-megabyte program and spend less than a minute on this search (this is genuine time it takes, not an exaggeration)? The matter of a fact is that authors of programs seem to do their best to help hackers in their work. Let us discuss one very typical example. Suppose your program goes something like this:
The most funny thing about this is that many authors actually find this kind of protection very reliable. Well indeed, the isRegistered() function is very complex and the verifications are scattered all over the program in abundance.
What is a hacker going to do to such a program? That’s right – he will just find a string, for example, «Register please!» and get its address. Now it’s not hard to find a piece of code like this one:
Now he is going to alter the only byte in the code, the one marked by an asterisk and there will be no demand of registration any more. Sometimes it’s enough to put a period here. In this case the time of hacking can be measured in seconds. Yet we are examining a more complex sort of protection – this testing is performed repeatedly. Get rid of an illusion that a hacker will try to find all of its occurrences (although it is not that difficult). He is merely going to alter a few starting bytes of a function IsRegidtered in such way that it is always going to return a TRUE value. This function may implement the most brilliant and the most reliable algorithm – but who needs it now?
Pondering over this given example we can reach two conclusions. First, the hackers’ task would get much more difficult, had he not found this place in the program so easily. Secondly, we cannot live with the fact that there is a theoretical chance to break a program by replacing just a few bytes. The right place was found only because the right string was found. Of course, this is a specific case. Instead of text there could be a resource id, if a message is stored as a text resource or a dialog box. There could be some distinctive number. Suppose an unregistered modification of your program limits some of its setting by 20. In this case a hacker might be looking for the code
To hamper the search of the necessary place for a hacker you should diguise such critical segments. Text strings (such as messages, filenames, Register key names etc.) should be encrypted for storage (in any, maybe even the most primitive way). The telltale constant numbers should be disguised like this:
Besides, the verification is not to be carried out in the very beginning of a program. It is preferable to have several testing procedures and perform them repeatedly. You can create a separate thread which performs such necessary check-ups periodically.
Let us take a more global look at the problem. How to achieve that your program theoretically cannot be broken by altering just a few bytes? Yes, it is possible. Consider an example:
Even now a hacker may find the function IsRegistered(). Now modifying it will only make your program stop working, because the constants which are located in the structure and are necessary for the work cannot be deciphered without the registration number. In other words, you should follow a simple rule – a value being verified should be used instead of being compared to a constant. So, we do not check for a presence of a registration number, we use it. Nowhere in a program a hacker may find what value this number should have. Let’s view one more example of this concept’s usage. Suppose an unregistered modification of your program allows not more than 40 records in some database. To simplify the matter we suggest that each user is described by a structure named CUser, and the database is just an array of the CUser structures. Usually there is something like
Having learned the aforementioned, you can make his life a bit more complex in this way, for example:
In this case, even if a hacker finds the verification (marked by an asterisk), he is going to get himself some very unpleasant and hard-to-find range check errors when the quantity of records exceeds forty.
It is harder to implement a protection if an unregistered program is supposed to display reminders. This variant is different in that a hacker is supposed to remove an «extra» to get a full-scale working version, not to add a missing function. To break is easier than to build, and this applies to this case, too. You can protect your program from cracking to some extent, if your program does something minute but necessary for your work when displaying a reminder. For instance, a reminder is implemented as a dialog box. When the WM_INIT message handler (dialog initializer) is executed, a timer can be set to one second. And when the WM_TIME timer handler is executed, you can initialize some necessary variables or perform another action which is necessary for the further work. If a hacker finds and suppresses the window output, simultaneously he renders the program inoperable.
Another evident way to protect your program from cracking is to check its integrity. For example, your program can count its checksum upon loading (the checksum of a file, not in memory). Although this cannot boost the speed of operation in any way, it can also help you to locate a virus infection or a violation of a program’s integrity which can occur during the program’s transfer via communication channels. It has to be kept in mind that, generally speaking, the integrity verification cannot guarantee the integrity itself, because a hacker may remove the verification subroutine itself. This is where the «chase» begins, whoever succeeds first. The integrity verification can be logically tied to a digital signature of a program (a.k.a. its certificate). There has been written a lot about it, so we won’t talk about it here.
Let’s address another problem now – how to prevent a distribution of the registered program? Generally, its a problem of a «traditional» copy protection. There is a lot written about it. Listed below are the most popular ways of protection.
This way of protection is practically not used any more. Firstly, it is very inconvenient for a user, secondly, it is unreliable because of unreliability of disk as an information medium. By the way, a common belief that this method is unreliable because any disk can be copied with a special program, is not true.
Aside from some apparent benefits, this method also has its disadvantages. Usage of two programs protected this way on one computer may turn out to be problematic. Because of a sensible cost, this method may be inappropriate for inexpensive programs. Besides, this method is only potentially reliable. In practice, however, we may encounter some very clumsy implementations (here’s a specific example: a verification function is located in a separate DLL and returns a true/false value «key present/ key not present».
Binding a program to equipment seriously limits a user, because a computer upgrade becomes impossible.
This binding may not be evident because program which has a complicated installer that carries out a large preparation work (entering settings into the Registry, installing common DLLs into the system directory, registering ActiveX controls) essentially binds a program to a specific copy of software installed on your computer.
If your program is distributed on CDs and its volume is not too big (that is, a program does not take up a whole CD), than you may consider filling the free space with the information which is needed for the installation. If you do it skillfully enough, than pirates would have a question arisen – is it worthwhile to issue a CD which is completely dedicated to your small program?
Well, pirates strive to place as much of different programs on a CD as possible, in order to increase the quantity of potential buyers. Your program may be small, yet have a bonus pack of useful, yet non-essential programs included with it. Pirates can easily «crop» your distribution package, therefore your installer should check for the presence of this extra information. You can also check if some files or directories previously absent from an original package have appeared on a CD.
And, just a little notice in conclusion. You can dramatically increase your program’s fortitude, yet it is going to take greater carefulness and attention than common programming takes. Here’s a small example: when proposing a method of protection by means of setting a counter of program launches, this article suggested to put this counter into a .ini file with a name that sounds intimidatingly scientific, and the most important thing was to forcibly set the same old date of modification for this file after each decrement of the counter. I hope that, upon reading this article, you will not store the name of this file as an open text. To manipulate this .ini-file you will probably use a WIN API function WritePrivateProfileString. Do you remember that Windows caches .ini-files to increase the operation speed? Here’s where such a situation may occur: you use the WritePrivateProfileString function, yet saving an .ini-file is delayed. You then set a date you need for the file. And then the cache is being dumped onto disk with a correct, yet undesirable date of modification specified. How to counter this problem is mentioned in the description of the mentioned function – I used this example to show, just how accurate a programming should be.
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