Securing Microsoft Silverlight: Client & Services Security Guide

1. Securing Microsoft Silverlight Shawn Wildermuth Microsoft Corporation

5. Silverlight Security Vectors Users/Hackers (Reflector, Silverlight Spy, Debuggers, Memory Profilers) Eavesdroppers (Packet Sniffers, etc.) Hackers/Personnel (Intrusion and Physical Security)

6. Securing the Client

7. Securing the Client (2) • Client Security Considerations • Code • XAML • Assets • Secrets • Isolated Storage • Data

8. Securing the Client (3) • Code • Limited Protection • Even with Obfuscation • XAML • Almost No Protection • Stored as Text • Assets • Almost No Protection

9. Securing the Client (4) • Secrets • Obfuscation Helps • Not Complete – Must Be Loaded Into Memory • Isolated Storage • No Protection • Accessible to Users – Keep Your Secrets Out of Here • Data • Limit Surface Area • Send Summary Data • Data Services’ Projections Are Helpful

10. Protecting You Intellectual Property • Silverlight does not protect your Algorithms • Unlike .NET: • Obfuscation only protects against decompilation • Code runs in the client • Client must be able to download assemblies

11. Protecting You Intellectual Property (2) • What is worth protecting? • Labor? No… • Unique implementations? Yes… • Sensitive data? Yes…

12. Protecting You Intellectual Property (3) • Hide it on the Server • Generate the XAML on the Server • Send only summary data to the client

13. Protecting Your XAP • Silverlight Apps Are Just Files • Protect like any other web file • Forms Authentication • Windows Authentication • Etc.

14. Protecting Your XAP (2) • For Apps with Login • XAP needs to be anonymous accessed • Compose at Runtime • Bootstrapper App or Composition (Prism, MEF, etc.)

15. Securing Services • Only Secure Methods in Silverlight • Token Based • Cookie Based • NTLM Based

16. Securing Services (2) Browser Silverlight App Network Call with Browser State (cookies, Session ID, NTLM) Network Call

17. Securing Services (3) • Why Not Basic Auth? • Insecure across the wire • (though could secure with SSL) • Uses Headers • Specifically forbidden using the HTTP Stacks

18. Securing Services (4) • Integrated Windows Authentication • Just Works • Assumes NTLM on the Platform • OSX is Problematic

19. Securing Services (5) • Cookie Based Auth • ASP.NET’s Forms Based Auth • Custom Encrypted Cookies • Never decrypt on client • Expire Cookies Frequently

20. Securing Services (6) • Token-based Security • Can use expiring tokens • Pass them in on web services • Not fool proof or ‘secure’ • Must also expire

21. Securing Services (7) • Add Service Reference Problem • Doesn’t play well with security • Must disable security when adding/refreshing • Trouble for building references at build-time

22. Securing Services (8) • ClientCredentials MyServiceClient client = new MyServiceClient(); client.ClientCredentials.UserName.UserName = "Frank"; client.ClientCredentials.UserName.Password = "P2ssw0rd"; client.GetNameCompleted += (s, args) => { theText.Text = args.Result; }; client.GetNameAsync();

23. Securing Services (9) • Using Forms Authentication Service • AuthenticationService (pre-built WCF) • Simple SOAP call to authenticate <%@ ServiceHost Language="C#" Service="System.Web.ApplicationServices.AuthenticationService" %> var proxy = new AuthenticationServiceClient(); proxy.LoginCompleted += (s, args) => { if (args.Result) { // Succeeded } }; proxy.LoginAsync("Frank", "P2ssw0rd", null, false);

24. Client HTTP Stack • Standard network stack goes through Browser • Good: • Uses cookies and NTLM • Looks and feels like the browser • Bad: • Only GET/POST are supported • Typically limited to two outbound requests

25. Client HTTP Stack (2) • Alternative: Client HTTP Stack • For specific scenarios: • Need PUT/DELETE • Need Custom Cookies • Need more control • status codes, bodies and headers

26. Client HTTP Stack (3) • Create New Request • Use WebRequestCreator’sClientHttp property: • Non-event-based, APM style WebRequestreq = WebRequestCreator.ClientHttp.Create(new Uri("http://api.search.live.net/qson.aspx?query=Silverlight", UriKind.Absolute)); req.BeginGetResponse(new AsyncCallback(r => { var res = req.EndGetResponse(r); varstrm = res.GetResponseStream(); }), null);

27. Client HTTP Stack (4) • Specify all Client HTTP Stack • Call WebRequest’sRegisterPrefix to specify: • Then all calls become client, even WebClient: boolhttpResult = WebRequest.RegisterPrefix("http://", WebRequestCreator.ClientHttp); WebClient client = new WebClient(); client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(OnDlComplete); client.DownloadStringAsync(new Uri("/template.xaml", UriKind.Relative));

28. Client HTTP Stack (5) • WebRequests Credentials Supported • For ClientHttp stack only, adds Authentication header var request = WebRequestCreator.ClientHttp.Create( new Uri("http://wildermuth.com", UriKind.Relative)); request.Credentials = new NetworkCredential("shawn", "p@ssw0rd"); request.UseDefaultCredentials = false; WebRequest.RegisterPrefix("http", WebRequestCreator.ClientHttp); var client = new WebClient(); client.Credentials = new NetworkCredential("shawn", "p@ssw0rd"); client.UseDefaultCredentials = false; client.DownloadStringCompleted += (s, a) => a.Result.ToArray(); client.DownloadStringAsync( new Uri("http://wildermuth.com", UriKind.Relative));

29. Questions?

30. Required Slide Track PMs will supply the content for this slide, which will be inserted during the final scrub. Track Resources • ASP.NET – http://www.asp.net/ • Silverlight – http://silverlight/ • Expression – http://www.microsoft.com/expression/ • Internet Explorer – http://www.microsoft.com/windows/internet-explorer/default.aspx

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