CODEWITHSUNDEEP
c#.netencryptioncryptography
A. Burlak
A. Burlak

Reputation: 25

A way to make a file decryptable only by specific program?

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!

Upvotes: 2

Views: 401

Answers (1)

akton
akton

Reputation: 14386

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.

Upvotes: 2

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