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I just recently found out here that it is possible (at least in c#) to look up private fields and properties due to reflection.
I was surprised, although I knew that somehow constructs like the DataContractSerializer class need the possibility to access them.
The question now is, if anyone can access every field in my classes, this is kind of insecure, isn't it? I mean what if someone has a private bool _isLicensed field. It could be changed easily!
Later I found out here that the field accessors are not meant as a security mechanism.
So how do I make my Application safe, meaning how do I prevent anyone other than me from changing essential status values inside my classes?
The question now is, if anyone can access every field in my classes, this is kind of insecure, isn't it?
Not everyone can. Only code with sufficient permissions - trusted code. Untrusted code is restricted quite a bit. On the other hand, if the person who wants to use reflection has your assembly, they can run trusted code on their own machine. That's not a new attack vector though, as if they've got your code they could also modify it to make the field public in the first place.
Basically, if code is running on their machine, you should expect them to be able to do pretty much anything with it. Don't rely on access modifiers to keep anything secret.
So how do I make my Application safe, meaning how do I prevent anyone other than me from changing essential status values inside my classes?
If the hostile user is running your code themselves, you pretty much can't. You can make it harder for them, but that's an arms race which is no fun.
So one option in some cases is not to let anyone else run your code - host it on the web in an environment you've locked down. That's not appropriate in all cases, of course.
If you have to let users run the code themselves, you need to weigh up the downsides of them tampering with the costs of making that tampering difficult. We can't really help you with that balancing act - we don't have any idea what your application is, or what the costs involved are (reputational, financial etc).
private public and so on are a part of http://en.wikipedia.org/wiki/Encapsulation. the use is to make your API clear and to avoid mistakes.
there is no solid way to avoid people messing with your program.
you may have noticed that all programs are cracked in a few days usually.
in .net it is VERY easy because of IL code been very readable http://ilspy.net/ and such allow you to take any DLL and just read it like C# code.
you can make it more annoying to read your code using obfuscator
http://en.wikipedia.org/wiki/List_of_obfuscators_for_.NET
but applications like http://de4dot.com/
break this VERY easily.
SecureString is a nice trick: https://msdn.microsoft.com/en-us/library/system.security.securestring%28v=vs.110%29.aspx
writing your code in low level language like c++ might make cracking your code really annoying. but soon a skilled hacker will do whatever he wants with your program.
the only option that might be safe is providing your application as a cloud service where the user only sees the screen output and sends keyboard/mouse input.
This was meant to be a comment for John Skeets answer but ran out of room..
Great answer by the way, but I also must add that code is not meant to be secure its meant to clearly defined.
Most developers know how to change classes and inject into classes. There are many utilities to not only decompile your code but to also allow injection into it.
I wouldn't spend to much effort trying to your make code more secure, I would try and expect the code to be changed. Many programming languages do not have such modifiers as private, public, internal, protected etc. They rely on the developers to understand the consequences of using this code on their own. These programming languages have been quite successful as the developers understand that modifying, calling or injecting into code the API does not specify has results that the developing company cant and will not support.
Therefore, expect your code to be modified and ensure your applications responds to invalid changes appropriately.
Sorry if this seems like a comment...
To add to all the other answers, a simple way of looking at it is this: If the user really wants to break your code, let them. You don't have to support that usage.
Just don't use access modifiers for security. Everything else is user experience.
So yeah, the question basically says it all. What do you gain when you ensure that private members / methods / whatever are marked private (or protected, or public, or internal, etc) appropriately?
I mean, of course I could just go and mark all my methods as public and everything should still work fine. Of course, if we'd talk about good programming practice (which I am a solid advocate of, by the way ), I'd mark a method as private if it should be marked as such, no questions asked.
But let's set aside good programming practice, and just look at this in terms of actual quantitative gain. What do I get for proper scoping of my methods, members, classes, etc.?
I'm thinking that this would most generally translate to performance gains, but I'd appreciate it if someone could provide more detail about it.
(For purposes of this question, I'm thinking more along C#.NET, but hey, feel free to provide answers on whatever language / framework you deem fit.)
EDIT: Most pointed out that this doesn't lead to performance gain, and yeah, thinking back, I don't even know why I thought that. Lack of coffee probably.
In any case, any good programmer should know about how proper scopes (1) help your code maintenance / (2) control the proper use of your library / app / package; I was kinda curious as to whether or not there was any other benefit you get from it that's not apparently obvious outright. Based on the answers below, it looks like it basically sums up to just those two things most importantly.
Performance has absolutely nothing to do with the visibility of methods. Virtual methods have some overhead, but that's not why we scope. It has to do with maintenance of code. Your public methods are the API to your class or library. You as a class designer want to provide some guarantee to the outside world that future changes aren't going to break other peoples code. By marking some methods private, you take away the ability for users to depend on certain implementations which allows you freedom to change that implementation at will.
Even languages that don't have visibility modifiers, like python, have conventions for marking methods as internal and subject to change. By prefixing the method with an _underscore(), you're signalling to the outside world that if you use that method, you do so at your own risk, as it can change at any time.
On the other hand, public methods are an explicit entry way into your code. Every effort should go towards making public methods backward compatible to avoid the pitfalls I described above.
By better encapsulation, you provide a better API. Only methods / properties that are of interest of the user of your class are available : visible.
Next to that, you ensure that certain variables that should not be called / modified, cannot be called/modified.
That's the most important thing. Why do you think this would lead to performance gains ?
As I see you gain two important features from proper scoping. You API is reduced in size and clearly focused on the task at hand.
Second, you get a less brittle implementation as you are free to change implementation details without altering the exposed API.
I cannot see how accessibility modifiers would affect performance in any way.
There are mainly two types of methods/properties.
That are helpful to perform a task to whoever consumes it. (Recommended Scope: Public)
That are helpful to the above methods to get their task done. (Recommended Scope: Private or Protected)
Type 1 methods are the only methods that any client code requires and does not need any other method. This avoids confusion, keeps things simple and prevents client code to do something wrong.
Type 2 methods are methods into which Type 1 methods are divided. They help Type 1 methods to complete their task and still allow them to be simple, concise, less complex and more readable. They are not really needed for client code but just the class/module itself.
A fair example would be of a car. What you have is a gas pedal, brakes, gearbox, etc. You don't have an interface to minor details for what is under the hood. That is for the mechanic.
In C# programming, it helps to make sure that your API/classes/methods/members are "easy to use correctly and difficult to use incorrectly".
Does reflection break the idea of private methods? Because private methods can be accessed from outside of the class? (Maybe I don't understand the meaning of reflection or miss something else, please tell me)
http://en.wikipedia.org/wiki/Reflection_%28computer_science%29
Edit:
If relection breaks the idea of private methods - do we use private methods only for program logic and not for program security?
Thanks
do we use private methods only for program logic and not for program security?
It is not clear what you mean by "program security". Security cannot be discussed in a vacuum; what resources are you thinking of protecting against what threats?
The CLR code access security system is intended to protect resources of user data from the threat of hostile partially trusted code running on the user's machine.
The relationship between reflection, access control and security in the CLR is therefore complicated. Briefly and not entirely accurately, the rules are these:
full trust means full trust. Fully trusted code can access every single bit of memory in the process. That includes private fields.
The ability to reflect on privates in partial trust is controlled by a permission; if it is not granted then partial trust code may not do reflection on privates.
See Link for details.
The desktop CLR supports a mode called "restricted skip visibility" in which the rules for how reflection and the security system interact are slightly different. Basically,
partially trusted code that has the right to use private reflection may access a private field via reflection if the partially trusted code is accessing a private field from a type that comes from an assembly with equal or less trust.
See
Link
for details
The executive summary is: you can lock partially trusted code down sufficiently that it is not able to use reflection to look at private stuff. You cannot lock down full trust code; that's why it's called "full trust". If you want to restrict it then don't trust it.
So: does making a field private protect it from the threat of low trust code attempting to read it, and thereby steal user's data? Yes. Does it protect it from the threat of high trust code reading it? No. If the code is both trusted by the user and hostile to the user then the user has a big problem. They should not have trusted that code.
Note that for example, making a field private does not protect a secret in your code from a user who has your code and is hostile to you. The security system protects good users from evil code. It doesn't protect good code from evil users. If you want to make something private to keep it from a user then you are on a fool's errand. If you want to make it private to keep a secret from evil hackers who have lured the user into running hostile low-trust code then that is a good technique.
Reflection does provide a way to circumvent Java's Access Protection Modifiers and therefore violates strict encapsulation as it realised in C++ and Java. However this does not matter as much as you might think.
Access Protection Modifiers are intended to assist programmers to develop modular well factored systems, not to be uncompromising gate keepers. There are sometimes very good reasons to break strict encapsulation such as Unit Testing and framework development.
While it may initially be difficult to stomach the idea that Access Protection Modifiers are easily circumventable, try to remember that there are many languages (Python, Ruby etc.) that do not have them at all. These languages are used to build large and complex systems just like languages which do provide access protection.
There is some debate on whether Access Protection Modifiers are a help or a hindrance. Even if you do value access protection treat it like a helping hand, not the making or breaking of your project.
Yes, but it is not a problem.
Encapsulation is not about security or secrets, just about organizing things.
Reflection is not part of 'normal' programming. If you want to use it to break encapsulation, you accept the risks (versioning problems etc)
Reflection should only be used when there are no better (less invasive) ways to accomplish something.
Reflection is for system-level 'tooling' like persistence mapping and should be tucked away in well tested libraries. I would find any use of reflection in normal application code suspect.
I started with "it is not a problem". I meant: as long as you use reflection as intended. And careful.
It's like your house. Locks only keep out honest people, or people who aren't willing to pick your lock.
Data is data, if someone is determined enough, they can do anything with your code. Literally anything.
So yes, reflection will allow people to do things you don't want them to do with your code, for example access private fields and methods. However, the important thing is that people will not accidentally do this. If they're using reflection, they know they're doing something they probably aren't intended to do, just like no one accidentally picks the lock on your front door.
No, reflection doesn't break the idea of private methods. At least not per se. There is nothing that says that reflection can't obey access restrictions.
Badly designed reflection breaks the idea of private methods, but that doesn't have anything to do with reflection per se: anything which is badly designed can break the idea of private methods. In particular, a bad design of private methods can also obviously break the idea of private methods.
What do I mean by badly designed? Well, as I said above, there is nothing stopping you from having a language in which reflection obeys access restrictions. The problem with this is that e.g. debuggers, profilers, coverage tools, IntelliSense, IDEs, tools in general need to be able to violate access restrictions. Since there is no way to present different different versions of reflection to different clients, most languages opt for tools over safety. (E is the counterexample, which has absolutely no reflective capabilities whatsoever, as a conscious design choice.)
But, who says that you cannot present different versions of reflection to different clients? Well, the problem is simply that in the classical implementation of reflection, all objects are reponsible for reflecting on themselves, and since there is only one of every object, there can be only version of reflection.
So, where does the idea of bad design come in? Well, note the word "responsible" in the above paragraph. Every object is responsible for reflecting on itself. Also, every object is responsible for whatever it is that it was written for in the first place. In other words: every object has at least two responsibilities. This violates one of the basic principles of object-oriented design: the Single Responsibility Principle.
The solution is rather simple: break up the object. The original object is simply responsible for whatever it was originally written for. And there is another object (called a Mirror because it is an object that reflects other objects) which is responsible for reflection. And now that the responsibility for reflection is broken out into a separate object, what's stopping us from having not one, but two, three, many Mirror Objects? One that respects access restrictions, one that only allows an object to reflect upon itself but not any other objects, one that only allows introspection (i.e. is read-only), one that only allows to reflect on read-only callsite information (i.e. for a profiler), one that gives full access to the entire system including violating access restrictions (for a debugger), one that only gives read-only access to the method names and signatures and respects access restrictions (for IntelliSense) and so on …
As a nice bonus, this means that Mirrors are essentially Capabilities (in the capability-security sense of the word) for reflection. IOW: Mirrors are the Holy Grail on the decade-long quest to reconcile security and runtime dynamic metaprogramming.
The concept of Mirrors was originally invented in Self from where it carried over into Animorphic Smalltalk/Strongtalk and then Newspeak. Interestingly, the Java Debugging Interface is based on Mirrors, so the designers of Java (or rather the JVM) clearly knew about them, but Java's reflection is broken.
Yes, reflection breaks this idea. Native languages also have some tricks to break OOP rules, for example, in C++ it is possible to change private class members using pointer tricks. However, by using these tricks, we get the code which can be incompatible with future class versions - this is the price we pay for breaking OOP rules.
It does, as other already stated.
However, I remember that in Java there can be a security manager active, that could prevent you from accessing any private methods, even with reflection, if you don't have the rights to do so. If you run your local JVM, such a manager is usually not active.
Yes, Reflection could be used to violate encapsulation and even cause incorrect behavior. Keep in mind that the assembly needs to be trusted to perform reflection, so there are still some protections in place.
Yes it breaks the encapsulation, if you want it to. However, it can be put to good use - like writing unit tests for private methods, or sometimes - as I have learned from my own experience - getting around bugs in third party APIs :)
Note that encapsulation != security. Encapsulation is an object oriented design concept and is only meant for improving the design. For security, there is SecurityManager in java.
Yes. Reflection breaks encapsulation principle. That's not only to get access to private members but rather expose whole structure of a class.
I think this is a matter of opinion, but if you are using reflection to get around the encapsulation put in place by a developer on a class, then you are defeating the purpose.
So, to answer your question, it breaks the idea of encapsulation (or information hiding), which simply states that private properties/methods are private so they cant be mucked with outside the class.
Reflection makes it possible for any CLR class to examine and manipulate properties and fields of other CLR classes, but not necessarily to do so sensibly. It's possible for a class to obscure the meaning of properties and fields or protect them against tampering by having them depend in non-obvious fashion upon each other, static fields, underlying OS info, etc.
For example, a class could keep in some variable an encrypted version of the OS handle for its main window. Using reflection, another class could see that variable, but without knowing the encryption method it could not identify the window to which it belonged or make the variable refer to another window.
I've seen classes that claim to act as "universal serializers"; they can be very useful if applied to something like a data-storage-container class which is missing a "serializable" attribute but is otherwise entirely straightforward. They will produce gobbledygook if applied to any class whose creator has endeavored to obscure things.
Yes, it does break encapsulation. But there are many good reasons to use it in some situations.
For example:
I use MSCaptcha in some websites, but it renders a < div> around the < img > tag that messes with my HTML. Then i can use a standard < img> tag and use reflection to get the value of the captcha's image id to construct a URL.
The image id is a private Property but using reflection i can get that value.
access control through private/protected/package/public is not primarily meant for security.
it helps good guys to do the right thing, but doesn't prevent bad guys from doing wrong things.
generally we assume others are good guys, and we include their code into our application without though.
if you can't trust the guy of a library you are including, you are screwed.
In both Java and C# it is possible to invoke a private method via reflection (as shown below).
Why is this allowed?
What are the ramifications of doing this?
Should it be taken away in a future version of the language?
Do other languages/platforms allow this?If I have this class in both Java and C#
Here is the example
public class Foo
{
private void say() { WriteToConsoleMethod("Hello reflected world"); }
}
where WriteToConsole() is language specific, then I can run the following to call the private say() method:
C#
Foo f = new Foo();
var fooType = f.GetType();
var mi = fooType.GetMethod("say", BindingFlags.NonPublic | BindingFlags.Instance);
mi.Invoke(f, null);
Java
Foo f = new Foo();
Method method = f.getClass().getDeclaredMethod("say", null);
method.setAccessible(true);
method.invoke(f, null);
As you can see, it is not obvious, but it's not difficult either.
In both Java and .NET, this is only allowed if you have sufficient permissions. Code that you run directly from the command line is (usually) operating in "full trust" mode. If you try doing the same thing in more restrictive environments, it will fail. Access control is more about encapsulation than security though. If you're operating at full trust, you've probably got enough access to launch native methods to poke around memory directly anyway...
Why is it allowed? Sometimes it can be handy. It should be treated with care, but it can be useful.
What are the ramifications? Your code becomes fragile; you're interacting with a type in a way it doesn't expect.
Should it be taken away in a future version of the language? It's a platform feature rather than a language feature in the first place, but no I don't think it should be removed.
Do other languages/platforms allow this? I'm not sure... I wouldn't be surprised though.
This is allowed because access restrictions are not meant to be a security measure.
It is kind of like putting locks on your house - they are a deterrent but they do nothing against someone who wants to use a battering ram to break down the door.
If for some reason you need to make sure that inappropriate callers cannot call a certain method (like if there is some kind of password/security risk), have a look at Code Access Security in .net. There is a way to tell the runtime to only allow a method to be called by callers who have a specific Authenticode signature.
The private/protected/public model of C++ became popular because C++ became popular, not because it was a great idea.
There are a lot of libraries out there that set methods to private that really should not have; some programmers will set nearly everything to private without understanding why you would do so, and some IDEs create scaffolding code with private set when it probably shouldn't be.
The result is that a lot of libraries have good, useful ideas, but have mistakes somewhere in their methods, and often those methods are marked private. The problem with private/protected/public and the normal constraints that come along with them is that you can't plan for everyone else's future use of your code. Even if you somehow managed to write bug-free code (which you won't), popular libraries will still find future uses you didn't anticipate. The author can't possibly determine which methods and variables will need to be accessed, overridden, tweaked etc for every single future use at the time they write it. It's just too much responsibility.
So this reflection trick you found breaks this model, but the truth is it should probably be EASIER to break, not more difficult. I would not look at this as a bug.
In fact in .Net you can use Reflector to take this approach even farther and avoid the real-time reflection calls in your code, to avoid the performance hit incurred when you find buggy code marked private. If you do so, try to avoid private declarations in the new code you write, to be nice to the next author who leverages your work.
Omar Al Zabir is looking for "a simpler way to do AOP style coding".
He created a framework called AspectF, which is "a fluent and simple way to add Aspects to your code".
It is not true AOP, because it doesn't do any compile time or runtime weaving, but does it accomplish the same goals as AOP?
Here's an example of AspectF usage:
public void InsertCustomerTheEasyWay(string firstName, string lastName, int age,
Dictionary<string, string> attributes)
{
AspectF.Define
.Log(Logger.Writer, "Inserting customer the easy way")
.HowLong(Logger.Writer, "Starting customer insert", "Inserted customer in {1} seconds")
.Retry()
.Do(() =>
{
CustomerData data = new CustomerData();
data.Insert(firstName, lastName, age, attributes);
});
}
Here are some posts by the author that further clarify the aim of AspectF:
AspectF fluent way to put Aspects into your code for separation of concern (Blog)
AspectF (google code)
AspectF Fluent Way to Add Aspects for Cleaner Maintainable Code (CodeProject)
According to the author, I gather that AspectF is not designed so much as an AOP replacement, but a way to achieve "separation of concern and keep code nice and clean".
Some thoughts/questions:
Any thoughts on using this style of coding as project grows?
Is it a scalable architecture?
performance concerns?
How does maintainability compare against a true AOP solution?
I don't mean to bash the project, but
IMHO this is abusing AOP. Aspects are not suitable for everything, and used like this it only hampers readability.
Moreover, I think this misses one of the main points of AOP, which is being able to add/remove/redefine aspects without touching the underlying code.
Aspects should be defined outside of the affected code in order to make them truly cross-cutting concerns. In AspectF's case, the aspects are embedded in the affected code, which violates SoC/SRP.
Performance-wise there is no penalty (or it's negligible) because there is no runtime IL manipulation, just as explained in the codeproject article. However, I've never had any perf problems with Castle DynamicProxy.
On a recent project, it was recommended to me that I give AspectF a try.
I took to heart the idea of laying all the concerns up front, and having the code that does the real work blissfully unaware of all the checks and balances that happened outside of it.
I actually took it a little further, and added a security "concern" that required credentials that were being received as part of a WCF request. It went off to the database and did what it had to. I did obvious validations, and the security check before running the actual code that would return the required data.
I found this approach quite a refreshing change, and I certainly liked that I had the source of AspectF to walk through as I was debugging and testing the service calls.
In the office, some argued that these concerns should be implemented as a decoration on a class / method. But it doesn't really matter where you decorate it, at some point somewhere, you need to say you wish to perform certain actions / checks. I like the fact that it's all laid out in-place, not as another code file, not as some kind of configuration file, and for once, not adding yet another decoration to a class / method.
I'm not saying it's true AOP - and I certainly think there are solutions and situations where it really isn't the best way of implementing your objectives, but given that it's just a couple of K of source files, that makes for a very light-weight implementation.
AspectF is basically a very clever way of chaining delegates together.
I don't think every developer is going to look at the code and say how wonderful it is to look at, indeed in our office it confused some of us! But once you understand what's going on, it's an inexpensive way of achieving much of what can be done by other approaches too.