I am doing a larger application which at some point would serialize/deserialize XML files. The problem is, that I need to make some of those XML files encrypted.
Basically, the encrypted one would be made by my professor for his students. It would be like a black-box, so my professor prepares a class in my application, serializes it and additionally, my app would encrypt the whole XML. Then student loads the XML to the application, but they don't know what's in it. I thought about a simple encryption, AES, whatever. I would store the key to encryption/decryption as bytes in my code.
But then it came to me, that every student could go for something like dotPeek, or something like this, disassembly my executable and then get the key and be able to decrypt every encrypted XML file. Now that is not something I can allow.
I was searching through the internet for possible solutions to my problem, but I couldn't quite find an answer.
Can you guys think of any way of doing that kind of thing? The app would be written in C# and would be running on Windows 7/10 if that matters.
If it is a multi-user application, then you need to ensure the ownership of the file by individual user authentication & authorization.
Server should be able to validate client incoming request and serve the authorized file accordingly.
Maintain different encryption keys for each user; this is to decrypt the file. Note that, having global-admin-enc-key is vulnerable in attack vector.
To prevent the code from re-engineered, you can obscure the code by obfuscation. It confuses the code for human. This thread also claims to have a protector.
How to prevent decompilation of any C# application
Related
I have a WinForms application which reads data from a sensitive file and performs calculations using that data. In order to keep the sensitive information from people's PCs, we decided to move the calculations to a web service, where the file will hide in a protected folder and only is accessible by the web service program itself.
Due to some complications it looks like it may not be possible to secure the server space in the required timeframe, so what we are now looking to do is use encryption to protect the file so that it can be safely distributed to people's PCs.
My question is this. Is is possible to encrypt a file (once, so a pre-encrypted file will be attached to the project) and then decrypt the file for use by the application without revealing
The sensitive information inside the file
The Encryption key used to decrypt the file
I know it is possible to generate source code from a .exe file so I would be looking for a solution that bears this in mind. I am new to this kind of app development so please excuse me if this is a stupid question and that what I am trying to do is not actually possible.
Cheers
No, it is not possible, you can only make it hard to do those two things. You can not make it impossible. All you can do is just make it hard enough it is not worth the effort to try, and that takes money to do (via specialized obfuscation software and paying experts in the field to look at your code and make it more secure)
My situation is as follows:
I have to deploy a series of .NET desktop applications consisting of a file with encrypted data and an executable that will access that data and decrypt some parts of it in runtime.
What I need to achieve is that each data container should only be decryptable by that specific .exe it is provided with.
The first idea was to encrypt the data using, say, the hash value of the .exe file as a symmetric key and during decryption calculate the hash value of the .exe file in runtime and decrypt the parts of the data container with it.
However, the problem with that approach is that the user can easily look into the .NET assembly with ILSpy or any other decompiler and discover the whole encryption algorithm which will enable the user to decrypt all the data containers in my series of applications.
Another solution that comes to my mind is to make a small C native library (that is less easy to decomplile) that will perform some manipulations with the .exe assembly information and generate a key for decryption based on it (let's consider the user lazy enough so that he will not try to intercept the key from the memory).
But ideally I wouldn't like to resort to any languages other than C# because porting the application to other platforms with Mono will require additional effort (P/Invokes and so).
So my question is: is there a way I can encrypt the data so that only a certain application would be able to decrypt it?
Of course I understand that in case of a local application it is impossible to keep the data absolutely secure but I need to make the 'hacking' at least not worth the effort. Are there any reasonable solutions or I will have to stick to one of my ideas I described above?
Thank you in advance!
The simple answer is no.
To encrypt and decrypt data, you need an algorithm and, optionally, a secret or key. If a computer can execute the algorithm, someone else can learn what it is. Ignoring decompilation and disassembly, a user could just look at the instructions executed by the CPU and piece together the algorithm.
This leaves the secret. Unfortunately, if the computer or program can access or derive a secret, so can someone with root or administrator rights on that computer for the same reasons above.
However, maybe you are just thinking about the problem the wrong way. If you want the program to access data that no one else can, consider making that data available from a server that users must authenticate to access. Use SSL so data is protected in transit and encrypt the data locally using a key that only the local user and local administrators can access. It is not perfect but it is about the best you are going to get in the general case.
If you need more protection than that, you may want to consider hardware dongles but this gets expensive and complex quite quickly.
Lets say my program is an Anti-Virus.
Lets also say I have a file, called "Signatures.dat". It contains a list of viruses to scan.
I would like to encrypt that file in a way that it can be opened my by anti-virus on any computer but the users wont able to see the content of that file.
How would I accomplish that task ?
I was looking at thigs like DPAPI, but I dont think that would work in my case because it's based on User's setting. I need my solution to be universal.
I've got a method to encrypt it, but then I am not sure how to store the keys.
I know that storing it in my code is really unsecure, so I am really not sure what to do at this point.
You want the computers of the users to be able to read the file, and you want the computers of the users to be unable to read the file. As you see, this is a contradiction, and it cannot be solved.
What you are implementing is basically a DRM scheme. Short of using TPM (no, that doesn't work in reality, don't even think about it), you simply cannot make it secure. You can just use obfuscation to make it as difficult as possible to reverse-engineer it and retrieve the key. You can store parts of the key on a server and retrieve it online (basically doing what EA did with their games) etc., but you probably will only make your product difficult to use for legitimate users, and anyone who really wants to will still be able to get the key, and thus the file.
In your example are you trying to verify the integrity of the file (to ensure it hasn't been modified), or hide the contents?
If you are trying to hide the contents then as has been stated ultimately you can't.
If you want to verify the file hasn't been modified than you can do this via hashes. You don't appear to have confused the two use-cases but sometimes people assume you use encryption to ensure a file hasn't been tampered with.
Your best bet might be to use both methods - encrypt the file to deter casual browsers, but know that this is not really going to deter anyone with enough time. Then verify the hash of the file with your server (use https, and ensure you validate the certificates thumbprints). This will ensure the file hasn't been modified even if someone has cracked your encryption.
I'm looking for a way to securely store an API key in a WP7 application. The key is a string and is currently hard coded into the code (see below). I know that someone with a reflector program could easily view this. Is there a better way to package this key as part of my app? Would a resource be more secure?
string key = "DSVvjankjnersnkaecjnDFSD44VDS23423423rcsedzcadERVSDRFWESDVTsdt";
Thank you in advance.
Have a look at Safeguard Database Connection Strings and Other Sensitive Settings in Your Code, it is a good read. Your question is under the "Hiding Keys in the Application Source Code" section.
Excerpt:
If you define the key in the application, in addition to obfuscating the assembly, try not to store the actual key bytes in the source code. Instead, implement key-generation logic using persistent characteristics, such as the encryption algorithm, key size, pass phrase, initialization vector, and salt (see an example at Encrypt and Decrypt Data Using a Symmetric (Rijndael) Key). This will introduce an extra layer of indirection, so the key will not be accessible by simply dumping the symbols from the application binary. As long as you do not change key-generation logic and key characteristics, the resulting key is guaranteed to be the same. It may also be a good idea not to use static strings as key-generation characteristics, but rather build them on the fly. Another suggestion would be to treat the assembly the same way as the data store should be treated, that is, by applying the appropriate ACLs. And only use this option as a last resort, when none of the other data protection techniques work and your only alternative is leaving sensitive data unencrypted.
I've read through all these answers, and I don't think there is any way you can securely embed this - regardless of where you put it, or how you obfuscate it. As long as its in your XAP and decoded within the application then it will always be available to hacking.
If you need to ship the key inside the xap with a reasonable degree of protection, then I think #maka's answer yields your best bet - obfuscate it as best you can - but don't think this will make you secure - i.e. don't do this for your mobile banking apps!
Alternatively, if you really need security then don't operate solely within the app - use a web server as well. For example, if you were doing a Facebook app and needed to somehow protect your facebook secret key, then you would need to redirect the user from your app to a web page on your server for authentication. That web page would then need to guide the user through the process of getting an access token - and then just that access token (along with the public appid) would need to go back to your app. And for those webservices which require knowledge of the secret key to accompany every call, then I'm afraid every single call will probably need to go via your server.
You can encrypt Api key with ProtectedData and then decrypt it in runtime. This is good tutorial how to encrypt data in Windows Phone: Encryption in Mango
May be you can encrypt it before hand and save it in app.config. And while reading it decrypt it using the same algorithm.
You could use DotFuscator to disable the ability to use reflector.
But, this will not allow you to change the key without recompiling.
In the past I've used the following method in other (web/winform-based) software:
http://weblogs.asp.net/jgalloway/archive/2008/04/13/encrypting-passwords-in-a-net-app-config-file.aspx
It's not an answer maybe, but sure it's a suggestion:
Store encrpyted key in a db. And store encrypted "db password" in app.config.
Use two proper string encrypt/decrypt algorithm, let's say algorithm x and y.
Put encrypted db password in app.config before to publish it.
Decypt app.config password(algo y) to connect the db for taking new encrpyted string(real one).
Close the connection and decyrpt new string with algorithm x if reflector/etc. not running.
Use it.
Dispose the object that holds the string.
Beforehand :
I have read indeed the other topics on SO, but I can't find an answer in them.
(The others are about config-files, or a list of techniques)
My question thus is very simple, though a bit subjective (I'll label it beforehand :-)) what is the easiest way..
File.Encrypt is pretty simple - one call (with one parameter).
Of course, it really depends on what you want the encryption for. File.Encrypt encrypts to the current account, which isn't much use if you're passing the file around. But, given your spec - i.e. easiest way to encrypt a file - it has to be a candidate!
Data Protection API in C#
Don't believe you have any security just because you encrypt a config file. If someone has access to the encrypted config file, and your executable, containing the password, it's likely to be possible to decrypt your configfile. It's just a little harder.
And say your config file contains passwords to database connections, it might be possible to get those passwords looking at the network packets.
Encryption is trivial with modern libraries: the hard part is securing the key(s).
So you need to look at what you're trying to secure, and what threats you are trying to secure against.
To encrypt a file so only the current user can see it on a client workstation, File.Encrypt is a good choice, or DPAPI with the CurrentUser scope.
For a configuration file on a single server, DPAPI using the LocalMachine scope is a good choice. You then need to make sure only authorized users are able to log in to the server. Here you're essentially delegating key management to Windows.
For a configuration file on a server farm, you need to share the key between the servers. RsaProtectedConfigurationProvide is a good choice, but you have more work ensuring that all servers have access to the same key, and that it is protected against unauthorized access (e.g. using a DACL).
I recommend the Cryptography Application block in Enterprise Library. Very easy, very flexible.