I was examining the ways of protecting my code from decompiling.
There are several good threads here describing obfuscation and code packing as the possible ways of protecting the code. However none of them is ideal, obfuscation doesn't work with reflection when the string method/property names are used. Many people do not recommend to use obfuscation at all.
So I currently decided not to go with any of the above. However, I have parts of the code where I need a sort of encryption, for example, a database connection string with an IP, login and password is stored inside the code as simple const string, same as email account data.
In ASP.NET there is an option to move the sensitive data to a .config file and encrypt it, but that requires the server key, i.e. linked to a single computer. I didn't read much about it, but I suppose something similar is available for desktop applications. But I need this to work on any computer where the application is installed.
And here is the question: are there ways to encode/protect such data so that it cannot be read along with decompiled code?
First advice is to never store anything sensitive in your code directly. You can always reverse engineer that, no matter how cleverly you try to obfuscate it.
I've read about things like breaking a password into several pieces, placing them at different places in the code and running them through a series of functions before finally using them... although this makes things harder, you can still always monitor the application using a debugger and ultimately you will be able to retrieve the secret information.
If I interpret your scenario correctly, what you have is code that is to be deployed at some client's premises and your code is connected to a database (which I suppose is also under the client's supervision), connecting to it requires a password. This password is known to that client, so trying to hide it from the client is rather useless. What you do want is to restrict access to that password from anybody who is not supposed to know it.
You typically achieve this by putting the sensitive information in a separate file in a folder that should have very restrictive permissions, only the application and a handful of selected people should have access. The application would then access the information when needed during runtime.
Additionally encrypting the separate file turns out to be a problem - if you do so then there is a key involved that again would have to be secured somehow - infinite recursion is on it's way :) Securing access to the file is often sufficient, but if you really require to be as secure as possible, then a solution is to use password-based encryption for the file. But the idea here is not to store the password in yet another location on the system, but rather as out-of-band information (e.g. in a physical vault) and entering the password when starting the application. This, too, has its problems: physical presence of a person is required for (re-)starting the application, and you could still retrieve the password from the RAM of the machine where the application is running on. But it is probably the best you can do without specialized hardware.
Another good alternative to password-based encryption would be to rely on OS-specific "password vaults" such as Windows' Isolated Storage, it's sort of a trade-off between not encrypting at all and keeping the password out-of-band.
This isn't an encryption answer, but one way to 'secure' this would be to make all your database calls through a web service. Your connection credentials would then be stored on your secure server and the clients pass all calls through there.
Nothing sensitive stored in your re-distributable at all...
I have grappled with this problem in the past and come up with three ways of dealing with the problem, but I'm not sure any of them are perfect:
Obfuscate or encrypt the value and hope for the best. Encryption, of course, is just an extra level of obfuscation since the key must be delivered with the rest.
Eliminate the need for the key itself by using one-way encryption instead. Use a private key to generate a public key. This can be used for licensing or password validation. You generate the licenses with the private key, but the public key can be used to validate them. Or you use the private key to generate a password that can be validated, but not reversed using the public key.
Create your own system-specific key-generation mechanism similar to that used by ASP.NET. You can limit the effect of someone reversing the encryption/obfuscation in step 1 by generating a unique key for each installation or site.
There are tons of methods, but the reality is that if you really want to protect your code, the only solution is to use "professional" products :-) don't try to reinvent the wheel. These products normally have options to encrypt strings. The real problem is another: without a professional product (and even WITH a professional product) an expert can simply put a breakpoint and look at the parameters passed to the library method (for example the one that opens the connections). Now... If you really really want to encrypt the strings of your code, it's quite easy. But would it be useful? No.
Now, just so that no one will mark this as "not an answer", I'll post some simple encryption/decryption code:
// Generate key. You do it once and save the key in the code
var encryptorForGenerateKey = Aes.Create();
encryptorForGenerateKey.BlockSize = 128;
encryptorForGenerateKey.KeySize = 128;
encryptorForGenerateKey.GenerateKey();
encryptorForGenerateKey.GenerateIV();
var key = encryptorForGenerateKey.Key;
var iv = encryptorForGenerateKey.IV;
// Encrypt: this code doesn't need to be in the program. You create a console
// program to do it
var encryptor = Aes.Create();
var encryptorTransformer = encryptorForGenerateKey.CreateEncryptor(key, iv);
string str = "Hello world";
var bytes = Encoding.UTF8.GetBytes(str);
var encrypted = encryptorTransformer.TransformFinalBlock(bytes, 0, bytes.Length);
var encryptedString = Convert.ToBase64String(encrypted);
Console.WriteLine(encryptedString);
// Decrypt: this code needs to be in the program
var decryptor = Aes.Create();
var decryptorTransformer = decryptor.CreateDecryptor(key, iv);
byte[] encrypted2 = Convert.FromBase64String(encryptedString)
var result = decryptorTransformer.TransformFinalBlock(encrypted2, 0, encrypted2.Length);
var str2 = Encoding.UTF8.GetString(result);
This code clearly isn't secure. Anyone can decompile the program, add a Console.WriteLine(str2) and recompile it.
You can of course encrypt your string before compiling it, but your code need that in plain text sometime if you are using a simple db or http url.
There is not a real protection in this case: Everyone can listen (breakpoint) to a specified method and when called see what's going on without really reading your code.
So no, there is not a real protection against this, also using obfuscation at some point you will call some .NET method with that plain text string, and everyone can read it.
You can for example put a COM or C++ dll for storing encrypted strings.
A unmanaged dll is not decompilable, however, expert people can of course understand the disassembly of a dll. And as said before, sometime you will need the plain data, and at that moment, there is no protection that can last.
The only thing you can do is to change your architecture.
For example, if your db is online and your application is a client application, you can connect using web services.
Then you can expose only the web services the user really need to use, there is no risk of user writing sql queries.
Then you can add the protection logic on the server instead that on the client.
If everything is offline there is not much you can do, you can make life harder using simple string encryption but it will never be a real protection.
As Lucas pointed out in its comment, if you have only one piece, then anybody decompiling your application can reverse-engineer it and decrypt your database passwords.
About storing credentials, my usual practice is to always store them in the application configuration file. If then I need to secure it, I use a SecureString and some encryption. And this could work for any kind of configuration information, not only credentials. There is a really good article about securing configuration files here: Encrypting Passwords in a .NET app.config File
Maybe you should read some more on encrypting the web.config http://learn.iis.net/page.aspx/141/using-encryption-to-protect-passwords/
Otherwise there isnt much you can do. Storing sensitive data in code isn't an option since anyone with a reflector tool can open it and see it. If you want code or variables to be invisible to everyone, you should create a webservice on a private server that accepts data, transforms it through it's magic and returns it to the client. In that way everything in between posting and retrieving the data is kept secret.
I am not sure if it is possible to protect your code at a client location, but a solution might be to store the password in Azure Key Vault and authenticate to it with Azure Active Directory. However, this might still be possible to reverse engineer. You can read more here: https://learn.microsoft.com/en-us/azure/key-vault/
Related
I want to do the below. What is the best way to achieve this?
I have a desktop app in C# which will be installed on multiple client machines.
The application is capable of doing an operation X but it needs some auxillary info which it can read from a file. This auxiliary info essentially provides some specifics that identify that machine where the operation should be run and what operation to run etc.
I will work with the client to get some of this auxilary info about his machine (say hostname/ip address etc) which I want to put in this file along with other info and generate it on my machine and share it with him/her to provide it to my software. I want to encrypt this data so that the structure of the data is not obvious to somebody who opens it. (I will get some of the machine identification info from the client, either via phone or email).
I want to somehow encrypt and secure this file such that only I can generate the file but any of my installations can read it. But since the contained info is specific to a machine it will be executed only on one machine (other machines will read but reject it since the given hostname/ip etc won't match that machine)
How do I do this? I want to make sure the below:
Only I can generate this file.
I need to somehow authenticate that this is generated only by me and not by somebody else.
But my software on client machines should be able to decrypt this.
I don't want to take a password from the customer etc. all the decryption logic should be in the installed software itself. I want to code it in.
When I researched this online, many talk about public and private cryptography but there they talk about encrypting with the public key and decrypting with the private key. But I don't think this will work since decryption is being done by my software at the client machine and so I shouldn't put the private key in my code. Because, from what I read, private key can generate public key so somebody could potentially generate that instruction file if I do this.
What is the best way to do this? Can I encrypt with private key and decrypt with public key? Is it ok if somebody gets hold of my public key (say they disassemble the C# code)? Any other good ways to encrypt and authenticate such that I hold the private data with me but code only harmless public keys/data in the application?
TIA.
Who are you trying to protect this from?
You are giving the end user your application binary. Assume they can decompile it and work out how it works. Or step through your code in a debugger, with access to the contents of every variable. Assume that an attacker can learn everything they need to know about how it works.
At best I would recommend creating a hash of the machine details and a salt value. Then create a signature of that hash.
Keep the salt and the public key of the signature as a constant in the application binary. Maybe XOR values together so an attacker has to think a little about how it works.
But anything more is pointless. Any attacker with more skills will just patch your program to delete the test entirely. So I wouldn't bother building anything too complicated.
Giving someone a program, and preventing them from using it, is like trying to make water not wet.
You have two questions
How do you encrypt the information, and
How can your client make sure the information came from you.
Those are orthogonal
I'll address the second on first - it's easier.
First, hash the file, and add the hash to the payload. Then generate a public/private key pair, then encrypt some known (but non-trivial) information with the private key and add that to the payload. You can distribute the public key with your app. If your app hashes the file and the hashes match and it can decrypt the known information and make sense of it, then it came from you and no one has changed it.
This is known as a digital signature. If you look up a digital signature provider and follow the docs, it should just work.
The encryption problem is more of an issue. There's pretty much no way to do what you want. If your app can decrypt the information using information you distribute with the application, then a determined bad guy can extract that key material and decrypt it.
However, you can use the RSA key container on the client to do the encryption when you install the app. The process is similar to using encrypted sections in a web.config file. Since you won't be following the encrypted config section cookbook the process is complicated.
I've done this before, but it was several jobs ago, so I don't have anything I can show you.
But, it will be encrypted so that it can be read only where it was encrypted. No two installations will recognize each others files.
That said...
Encryption seems like a heavy hammer to prevent your customers from being able to guess "the structure of the data [so that it] is not obvious to somebody who opens it"
Unless you have something worth protecting, you can probably get away with obfuscating the data. For example, you could have the data as JSON, but then use GetBytes on a Utf8Encoding to get a byte[] and convert that to a hex string. A determined hacker could decompile you code, figure out what you've done and reverse it, but that doesn't seem like a threat you really need to worry about.
I have Created a C# Desktop Windows form Application and I have created a setup for that. In the C:\Programs files app folder I have a JSON file. I need to protect it from accessing by anyone (I need to protect the data). What should I do?
You can't. If the intruder have access to the computer with the Administrator rights (or even more - a physical access to the hardware), then any protection will be useless.
You can use some kind of encryption, code obfuscation and some anti-debugging techniques to make it harder to retrieve the data, but qualified intruder with the appropriate access level will be able to access the data in the moment when you will decrypt it.
The only working way is to completely remove the secret data from the client's computer and move it to the your secure server alongside with the processing of such a data. So, client sends the inputs to your server, the server performs the processing using the secret data and sends back ready-to-use results.
First of all: it's impossible to make it un-breakable - I won't argue on this. Then you can simply encrypt it with a simple Blowfish algorithm and keep the key hardcoded.
You can use a more secure algorithm if you want so.
Easiest solution is to use a binary serialization format instead of json. This will make it much harder to understand and decode. Or just hardcode the data instead. Most people lack the knowledge to do anything meaningfull with a binary chunk of data, or an assembly for that matter.
A more complicated solution would be to sign the data, as this would allow you to only hardcode the key. A related alternative is Encryption. Encryption is sufficient but not necessary for ensuring the integrity of the data, but is not really more difficult to apply, see encrypting data.
Whatever you do you cannot really prevent a sufficiently determined and knowledgeable attacker. It is possible to decompile the program and extract or replace any secrets therein. The only truly secure way would be to prevent access to the files in the first place, by moving it to the web for example.
I had a similar requirement and decided to encrypt the data.
I used the package "AuthenticatedEncryption" (available from NuGet ) and could hard-code the key in my code.
NuGet: https://www.nuget.org/packages/AuthenticatedEncryption/
Guthub: https://github.com/trustpilot/nuget-authenticated-encryption
I can do this, as my main purpose is more to make the data unreadable to users and I don't expect it to be unbreakable.
Even so, I change the key every few releases.
For my ~70Kb JSON file I only load it once at the start of the program, so performance is not a problem. Not that I anyway notice anything!
To access a API, I have to have a secret key. How would you approach storing that secret key, if this is going to be used on multiple machines?
I read this answer, and if I understand it correctly, besides some obfuscation, there's no point doing anything more?
It's not easy because IL code is readable. And the IL code easily gain from a binary like DLL or EXE using IL Disassembler: ildasm.exe.
The solution that #miniHessel said, downloading the code from a server using SSL is also not a safety solution, because a client on his/her own machine can track the SSL communication doing a "MITM attack" with a proxy like Fiddler or any other app. We have a lot.
We can only make things more difficult:
One solution is to encrypt the secret and keep the encrypted secret in the code. (before you use it you can decrypt it)
Better if you cut the encrypted secret to multiple parts and keep it different place in the code. And merge them before you decrypt it.
Give the variables and functions innocent name, so noone can figure out what the content is.
A good encryption/decryption solution is here: Encrypting & Decrypting a String in C#
I'm looking for a secure way to encrypt and decrypt a string in a Visual Studio Project (in C#). I found that there is native DES classes, but it's not secure enough. Do you have any suggestions?
UPDATE :
OK then, the question is : What's the most secure way to encrypt/decrypt a string without too much hassle (aka having to install external tools, etc. An external library is fine though). And where to put the secret "key" (is compiling the value inside the code secure enough?).
Update #2
If I'm using something like this code to save encrypted string in a config file :
using System.Security.Cryptography;
using System.Security;
byte[] encrypted = ProtectedData.Protect(StrToByteArray("my secret text"), null, DataProtectionScope.LocalMachine);
byte[] derypted = ProtectedData.Unprotect(encrypted , null, DataProtectionScope.LocalMachine);
Is this secure enough? I guess that with the "LocalMachine" parameter instead of "User" parameter, somebody could just write an application in .net, put it on the machine and execute it to decrypt the encrypted string. So if I want it more secure, I'll have to have a config file different for each user? Am I understanding that correctly?
To answer your second question, no, storing the encryption key in the executable, even obfuscated, is not secure at all. It'll keep casual prying eyes out, but not those with an hour to devote to walking through your decompiled source.
Think hard about where to store your encryption key - it looks like that'll be your weak point. And yes, this is a hard problem to solve. The most secure way to store encryption keys is not to - require the user to type a password, or require external hardware, like a key fob.
If you're encrypting contents intended to be read only on a single machine or by a single domain user, consider the Data Protection API (DPAPI). It takes the encryption key out of your hands - it uses the user's Windows credentials as the key.
I've got a little more detail in another answer here: Persistent storage of encrypted data using .Net
Regarding your second edit (is DataProtectionScope.LocalMachine good enough?); this MSDN blog entry summarizes it well:
Setting a scope of
DataProtectionScope.CurrentUser
encrypts the data so that only the
currently logged on user can decrypt
it. Switching to
DataProtectionScope.LocalMachine
allows any process running on the
current machine to decrypt the data.
This could be useful in a server
scenario, where there are no untrusted
logins to the machine, but for a
general purpose workstation using
LocalMachine encryption is almost
equivalent to using no encryption at
all (since anybody logged in can get
at the data).
It also has AES.
If I read your update correctly, you basically want to conceal some string constant from a sysadmin snooping around your assembly.
There is no way to make it impossible that someone with too much time extracts your string constant eventually. But you can annoy them, hoping that they give up trying before they unmask your secret.
One way to achieve that are Obfuscation Tools. These obfuscate your compiled assembly as much as possible, making it much harder to follow program flow when decompiling it with Reflector. Try it. If your string constant is still not hidden enough, you can additionally invent your own scheme to make it harder to find.
If you need more security, the almost only option is to not give the relevant parts of the code to the user. Create a web service that contains the secret parts of your application and secure the connection with SSL/TLS.
Try using AesManaged.
That depends on your definition of secure enough. You may use triple DES. .Net also has native Rijandel class. Is it secure enough? http://www.obviex.com/samples/Encryption.aspx
Using a well tested and accepted library is a good idea too...
http://www.bouncycastle.org/csharp/
I have an application that requires a secure way to store its configuration. There are users that can change the configuration. I need some sort of signature scheme where I can verify that the config file has not changed with out a valid user. I had thought about using RSA, where the private key is encrypted with the users password, and the public key is used to sign the config. However there is nothing to prevent someone from changing the user file and adding their own public key, thus circumventing my security. Any ideas?
You could just keep the file encrypted, and only allow editing from within your application. This would prevent users from editing the configuration from any tool other than yours, which could do the authentication to verify that the user is a "valid user".
Of all the methods listed, key management is the true weakness on a client machine. The key is required to decrypt. Using another key to encrypt that key is no stronger. Obfuscation is a start.
What I use is a separate assembly that contains our encryption code. The key is then stored via a technique called Steganography. I encode the key in the logo of application. This key is then encrypted using a known value of the software. In one case, it may be the checksum of a specific assembly. Thus anyone that makes any change to that file will break the system. This is by no means any more secure, but its all about hiding details. and raising the level of difficulty from casual to determined. From there, I then run the assembly through an obfuscator and string encryptor. This breaks Reflector with a crash when attempting to view the assembly and thus makes its more difficult to learn what is going on.
The issue with these strategies, is that if you attach an debugger then you get the data in the clear since you may store the values in a string after the encryption/decryption process. To combat this, but not eliminate, I use the System.Security.SecureString class and do not keep data in the clear.
The goal is to break reflector, stop simple attacks of just using the .NET Framework to decrypt the data, stop dictionary attacks by employing a random salt, allow easy string handling by URLEncoding the encrypted buffer, proper use of an Initialization Vector.
There is no way to fully secure a stand-alone Client application. The only way would be to do a checksum on the file and validate it to a/the server. The method of signing the file is less important than how you verify what is in fact signed.
A start to securing the client application is with Obfuscation. Thereafter your encryption is next in line.
For the actual signature, even a SHA series of hashes should do the job for you. An example using SHA512 is as follows:
FileStream fs = new FileStream(#"<Path>", FileMode.Open);
using (SHA512Managed sha512 = new SHA512Managed ())
{
byte[] hash = sha512.ComputeHash(fs);
string formatted = string.Empty;
foreach (byte b in hash)
{
formatted += b.ToString("X2");
}
}
These contradicts:
"I can verify that the config file has not changed with out a valid user"
"there is nothing to prevent someone from changing the user file"
You should just find a way to protect your "user file" first. By encrypting it with a key nobody can edits (except determined crackers) or otherwise. And then your RSA scheme will work.
Do note that, however, there is NO way to protect an application that runs entirely on the client from a determined cracker.
For most applications, though, you DON'T need perfect security. Maybe you should think about how much security is actually "enough" for your application first.
If you, however, needed perfect security, then you might need to add a server-side component OR add human-intervention into the process such as having an administrator controls the user file.
Encrypt the "user file" with the admin's passwords. And then whenever someone wants to change the user file, the administrator's consent is then needed.
I think what I will do is keep a private key(A) in the office. I will ship the app with an public private pair(B), signed with the private(A) that only I know. I will use the public private pair(B) I ship to sign everything on the config files. Thus there will be a verifiable set of RSA keys(B), that can't be change, because the private key(A) used to verify them is in the office, and the public key(A) is hard coded.