Non-DI aware scenarios for Data Protection in ASP.NET Core

By Rick Anderson

The ASP.NET Core Data Protection system is normally added to a service container and consumed by dependent components via dependency injection (DI). However, there are cases where this isn't feasible or desired, especially when importing the system into an existing app.

To support these scenarios, the Microsoft.AspNetCore.DataProtection.Extensions package provides a concrete type, DataProtectionProvider, which offers a simple way to use Data Protection without relying on DI. The DataProtectionProvider type implements IDataProtectionProvider. Constructing DataProtectionProvider only requires providing a DirectoryInfo instance to indicate where the provider's cryptographic keys should be stored, as seen in the following code sample:

using System;
using System.IO;
using Microsoft.AspNetCore.DataProtection;

public class Program
{
    public static void Main(string[] args)
    {
        // Get the path to %LOCALAPPDATA%\myapp-keys
        var destFolder = Path.Combine(
            System.Environment.GetEnvironmentVariable("LOCALAPPDATA"),
            "myapp-keys");

        // Instantiate the data protection system at this folder
        var dataProtectionProvider = DataProtectionProvider.Create(
            new DirectoryInfo(destFolder));

        var protector = dataProtectionProvider.CreateProtector("Program.No-DI");
        Console.Write("Enter input: ");
        var input = Console.ReadLine();

        // Protect the payload
        var protectedPayload = protector.Protect(input);
        Console.WriteLine($"Protect returned: {protectedPayload}");

        // Unprotect the payload
        var unprotectedPayload = protector.Unprotect(protectedPayload);
        Console.WriteLine($"Unprotect returned: {unprotectedPayload}");

        Console.WriteLine();
        Console.WriteLine("Press any key...");
        Console.ReadKey();
    }
}

/*
 * SAMPLE OUTPUT
 *
 * Enter input: Hello world!
 * Protect returned: CfDJ8FWbAn6...ch3hAPm1NJA
 * Unprotect returned: Hello world!
 *
 * Press any key...
*/

By default, the DataProtectionProvider concrete type doesn't encrypt raw key material before persisting it to the file system. This is to support scenarios where the developer points to a network share and the Data Protection system can't automatically deduce an appropriate at-rest key encryption mechanism.

Additionally, the DataProtectionProvider concrete type doesn't isolate apps by default. All apps using the same key directory can share payloads as long as their purpose parameters match.

The DataProtectionProvider constructor accepts an optional configuration callback that can be used to adjust the behaviors of the system. The sample below demonstrates restoring isolation with an explicit call to SetApplicationName. The sample also demonstrates configuring the system to automatically encrypt persisted keys using Windows DPAPI. If the directory points to a UNC share, you may wish to distribute a shared certificate across all relevant machines and to configure the system to use certificate-based encryption with a call to ProtectKeysWithCertificate.

using System;
using System.IO;
using Microsoft.AspNetCore.DataProtection;

public class Program
{
    public static void Main(string[] args)
    {
        // Get the path to %LOCALAPPDATA%\myapp-keys
        var destFolder = Path.Combine(
            System.Environment.GetEnvironmentVariable("LOCALAPPDATA"),
            "myapp-keys");

        // Instantiate the data protection system at this folder
        var dataProtectionProvider = DataProtectionProvider.Create(
            new DirectoryInfo(destFolder),
            configuration =>
            {
                configuration.SetApplicationName("my app name");
                configuration.ProtectKeysWithDpapi();
            });

        var protector = dataProtectionProvider.CreateProtector("Program.No-DI");
        Console.Write("Enter input: ");
        var input = Console.ReadLine();

        // Protect the payload
        var protectedPayload = protector.Protect(input);
        Console.WriteLine($"Protect returned: {protectedPayload}");

        // Unprotect the payload
        var unprotectedPayload = protector.Unprotect(protectedPayload);
        Console.WriteLine($"Unprotect returned: {unprotectedPayload}");

        Console.WriteLine();
        Console.WriteLine("Press any key...");
        Console.ReadKey();
    }
}