Get started with the Data Protection APIs in ASP.NET Core

Basically, protecting data consists of the following steps:

1. Create a data protector from a data protection provider.
2. Call the Protect method with the data you want to protect.
3. Call the Unprotect method with the data you want to turn back into plain text.

Most frameworks and app models, such as ASP.NET Core or SignalR, already configure the data protection system and add it to a service container that is accessed via dependency injection. The following sample demonstrates:

• Configuring a service container for dependency injection and registering the data protection stack.
• Receiving the data protection provider via DI.
• Creating a protector.
• Protecting then unprotecting data.

using System;
using Microsoft.AspNetCore.DataProtection;
using Microsoft.Extensions.DependencyInjection;

public class Program
{
    public static void Main(string[] args)
    {
        // add data protection services
        var serviceCollection = new ServiceCollection();
        serviceCollection.AddDataProtection();
        var services = serviceCollection.BuildServiceProvider();

        // create an instance of MyClass using the service provider
        var instance = ActivatorUtilities.CreateInstance<MyClass>(services);
        instance.RunSample();
    }

    public class MyClass
    {
        IDataProtector _protector;

        // the 'provider' parameter is provided by DI
        public MyClass(IDataProtectionProvider provider)
        {
            _protector = provider.CreateProtector("Contoso.MyClass.v1");
        }

        public void RunSample()
        {
            Console.Write("Enter input: ");
            string input = Console.ReadLine();

            // protect the payload
            string protectedPayload = _protector.Protect(input);
            Console.WriteLine($"Protect returned: {protectedPayload}");

            // unprotect the payload
            string unprotectedPayload = _protector.Unprotect(protectedPayload);
            Console.WriteLine($"Unprotect returned: {unprotectedPayload}");
        }
    }
}

/*
 * SAMPLE OUTPUT
 *
 * Enter input: Hello world!
 * Protect returned: CfDJ8ICcgQwZZhlAlTZT...OdfH66i1PnGmpCR5e441xQ
 * Unprotect returned: Hello world!
 */

When you create a protector you must provide one or more Purpose Strings. A purpose string provides isolation between consumers. For example, a protector created with a purpose string of "green" wouldn't be able to unprotect data provided by a protector with a purpose of "purple".

Tip

Instances of IDataProtectionProvider and IDataProtector are thread-safe for multiple callers. It's intended that once a component gets a reference to an IDataProtector via a call to CreateProtector, it will use that reference for multiple calls to Protect and Unprotect.

A call to Unprotect will throw CryptographicException if the protected payload cannot be verified or deciphered. Some components may wish to ignore errors during unprotect operations; a component which reads authentication cookies might handle this error and treat the request as if it had no cookie at all rather than fail the request outright. Components which want this behavior should specifically catch CryptographicException instead of swallowing all exceptions.

Use AddOptions to configure custom repository

Consider the following code which uses a service provider because the implementation of IXmlRepository has a dependency on a singleton service:

public void ConfigureServices(IServiceCollection services)
{
    // ...

    var sp = services.BuildServiceProvider();
    services.AddDataProtection()
      .AddKeyManagementOptions(o => o.XmlRepository = sp.GetService<IXmlRepository>());
}

The preceding code logs the following warning:

Calling 'BuildServiceProvider' from application code results in an additional copy of singleton services being created. Consider alternatives such as dependency injecting services as parameters to 'Configure'.

The following code provides the IXmlRepository implementation without having to build the service provider and therefore making additional copies of singleton services:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<DataProtectionDbContext>(options =>
        options.UseSqlServer(
            Configuration.GetConnectionString("DefaultConnection")));

    // Register XmlRepository for data protection.
    services.AddOptions<KeyManagementOptions>()
    .Configure<IServiceScopeFactory>((options, factory) =>
    {
        options.XmlRepository = new CustomXmlRepository(factory);
    });

    services.AddRazorPages();
}

The preceding code removes the call to GetService and hides IConfigureOptions<T>.

The following code shows the custom XML repository:

using CustomXMLrepo.Data;
using Microsoft.AspNetCore.DataProtection.Repositories;
using Microsoft.Extensions.DependencyInjection;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;

public class CustomXmlRepository : IXmlRepository
{
    private readonly IServiceScopeFactory factory;

    public CustomXmlRepository(IServiceScopeFactory factory)
    {
        this.factory = factory;
    }

    public IReadOnlyCollection<XElement> GetAllElements()
    {
        using (var scope = factory.CreateScope())
        {
            var context = scope.ServiceProvider.GetRequiredService<DataProtectionDbContext>();
            var keys = context.XmlKeys.ToList()
                .Select(x => XElement.Parse(x.Xml))
                .ToList();
            return keys;
        }
    }

    public void StoreElement(XElement element, string friendlyName)
    {
        var key = new XmlKey
        {
            Xml = element.ToString(SaveOptions.DisableFormatting)
        };

        using (var scope = factory.CreateScope())
        {
            var context = scope.ServiceProvider.GetRequiredService<DataProtectionDbContext>();
            context.XmlKeys.Add(key);
            context.SaveChanges();
        }
    }
}

The following code shows the XmlKey class:

public class XmlKey
{
    public Guid Id { get; set; }
    public string Xml { get; set; }

    public XmlKey()
    {
        this.Id = Guid.NewGuid();
    }
}