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SPS Ozarks 2012: Kerberos Survival Guide
This document provides an overview and agenda for a Kerberos survival guide presentation. The presentation will cover Kerberos logon process, accessing a web site using Kerberos, miscellaneous Kerberos information, and complex Kerberos configurations. It includes dependencies, service principal names (SPNs), and troubleshooting tools for Kerberos. The presentation aims to provide essential information about Kerberos without overcomplicating details.
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SPS Ozarks 2012: Kerberos Survival Guide
- 1. Kerberos Survival Guide Presentedby: JD Wade, Senior SharePoint Consultant MCTS & MCITP: SharePoint 2010, Configuring Mail: jd.wade@hrizns.com Blog: http://wadingthrough.com LinkedIn: JD Wade Twitter: http://twitter.com/JDWade Horizons Consulting, Inc. http://www.hrizns.com
- 2. Agenda •Overview •Logon Process •Accessing aWeb Site •Miscellaneous Information •The Really Complicated Stuff
- 3. Kerberos Massachusetts Institute of Technology
- 4. Details Out ofScope •Renewing tickets •Ticket expiration •Keys •Authenticator •TGT Structure •Service Ticket Structure •Encryption/Decryption •Multiple domains/forests
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- 8. Service Principal Name ServiceClass Host Name Port HTTP/website:80
- 9. Service Classes allowedby host alerter clipsrv dnscache http msiserver netman policyagent rpc scardsvr scm time wins appmgmt dcom eventlog ias mcsvc nmagent protectedstorage rpclocator scesrv seclogon trksvr www browser dhcp eventsystem iisad netdde oakley rasman rpcss Schedule snmp trkwks fax cifs dmserver plugplay min netddedsm remoteaccess rsvp spooler ups cisvc dns messenger netlogon replicator samss Tapisrv w3svc
- 10. Kerberos •Benefits •Delegated Authentication •Interoperability •More Efficient Authentication •Mutual Authentication •Reasons to Use •Need Auditing at the Data Sources •Data Sources contain Row Level Security •Otherwise, DO NOT USE IT!
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- 21. Kerberos •IIS – Chattyby default (make sure you do this!) •IIS6 – See MS KB 917557 •IIS7 – See MS KB 954873
- 22. <system.webServer> <security> <authentication> <windowsAuthentication enabled="true" useAppPoolCredentials="true" /> </authentication> </security> </system.webServer>
- 24. Troubleshooting Tools •Knowledge •SetSPN •Windows 2008ADUC or ADSIEdit •Windows Security Logs and IIS Logs •Klist •Netmon/Wireshark and Fiddler •IIS7 Failed Request Tracing •Kerberos Logging •Event Logging and/or Debug Logs
- 25. Why So Many StupidSettings?
- 28. Web Srv1 Srv2 Srv3 Srv4 Datamart Cubes
- 29. For all of2007 Web Srv1 Srv2 Srv3 Srv4 Datamart Cubes
- 30. Web Srv1 Srv2 Srv3 Srv4 Datamart Cubes
- 31. FBA Kerberos
- 32. Web Srv1 Srv2 Srv3 Srv4 Datamart Cubes
- 34. For 2010 &2013 • Uses Protocol Transition (Domain limited) (Constrained Only) • Excel Services • Visio Services • PerformancePoint • InfoPath Form Services • Does NOT Use Protocol Transition (Forest limited) (Unconstrained or Constrained) • SQL Reporting Services • BCS • Access Services • Project Server • Doesn’t usually require Kerberos • PowerPivot for SharePoint Server
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- 36. References •Ken Schaefer’s Multi-PartKerberos Blog Posts: http://www.adopenstatic.com/cs/blogs/ken/archive/2006/10 /20/512.aspx •What Is Kerberos Authentication? http://technet.microsoft.com/en- us/library/cc780469%28WS.10%29.aspx •How the Kerberos Version 5 Authentication Protocol Works http://technet.microsoft.com/en- us/library/cc772815%28WS.10%29.aspx •Explained: Windows Authentication in ASP.NET 2.0 http://msdn.microsoft.com/en-us/library/ff647076.aspx
- 37. References •Kerberos Authentication Toolsand Settings http://technet.microsoft.com/en- us/library/cc738673%28WS.10%29.aspx •How To: Use Protocol Transition and Constrained Delegation in ASP.NET 2.0 http://msdn.microsoft.com/en-us/library/ff649317.aspx •Spence Harbar’s Blog http://www.harbar.net
- 38. Housekeeping • Follow SharePointSaturday Ozarks on Twitter @SPSOzarks hashtag #SPSOzarks • Stop by and thank our sponsors for making this event possible! • Fill out and turn in evaluation forms to be eligible for the end-of- day raffle. You must be present to win. • Don’t miss “This Modern Station” tonight at Waxy O’Shea’s! 38 | SharePoint Saturday St. Louis 2012
- 39. Thanks to Our Sponsors! Platinum
- 40. Thanks to Our Sponsors!
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- 43. •Kerberos is anopen authentication protocol. Kerberos v5 was invented in 1993 at MIT. •Authentication is the process of proving your identity to a remote system. • Your identity is who you are, and authentication is the process of proving that. In many systems your identity is your username, and you use a secret shared between you and the remote system (a password) to prove that your identity. •User password is encrypted as the user key. User key is stored in credentials cache. Once the logon session key is received, the user key is discarded. •Service password is encrypted as the service key. •KDCs are found through a DNS query. Service registered in DNS by DCs.
- 44. •Showing detail behindwhat is happening inside of KDC but for day-to-day, use can just remember KDC •Another reason for simplification: encryption upon encryption upon encryption…just remember it is encrypted •This is a Windows-centric Kerberos presentation •Load balanced solutions need service account •All web applications hosted using the same SPN have to be hosted with the same account •Use A records, not CNAME records
- 45. •Terms •Key Distribution Center(KDC) – In Windows AD, KDC lives on domain controllers (DC), KDCs share a long term key across all DCs. •KDC security account database – In Windows, it is Active Directory •Authorization Service (AS) – part of the KDC •Ticket Granting Service (TGS) – part of the KDC •Ticket Granting Ticket (TGT) - A user's initial ticket from the authentication service, used to request service tickets, and meant only for use by the ticket granting service. Keeps the user from having to enter password each time a ticket is requested.
- 46. Tickets •Ticket Granting Ticket(TGT) •A user's initial ticket from the authentication service •Used to request service tickets •Meant only for use by the ticket-granting service. •Service ticket for the KDC (service class = krbtgt) •Service Ticket •Enables the ticket-granting service (TGS) to safely transport the requester's credentials to the target server or service.
- 47. Tools •Knowledge •SetSPN •Windows Security Logs •Windows2008 ADUC or ADSIEdit •Kerbtray or Klist •Netmon and Fiddler •IIS Logs and IIS7 Failed Request Tracing •LDP •Kerberos Logging •Event Logging and/or Debug Logs
- 48. •Troubleshooting • Have user logon and logoff if they don’t regularly: TGTs are only renewable for so long and then they expire (7 day default), then password has to be re- entered. • Remember that authenticators contain the current time. Check for time sync issues.
- 49. •Common Issues • Missing SPN • Duplicate SPN • SPN assigned to wrong service account • Times are out of sync • Client TGT expired (7 days) • IE and non-default ports
- 50. •Request TGT (Rememberthere is even more complexity) 1. User (client) logs into workstation entering their password. 2. Client builds an authentication service request containing the user’s username (KPN), the SPN of the TGS, and encrypts the current time using the user’s password as an authenticator. 3. Client sends these three items to the KDC. 4. KDC get user’s password from AD, decrypts time and verifies it is valid. 5. AS generates a logon session key and encrypts with the user’s password. AS generates a service ticket which contains a logon session key and the user’s KPN encrypted with the AS shared key. This is a special service ticket called a Ticket Granting Ticket (TGT).
- 51. •Request TGT (Rememberthere is even more complexity) 6. KDC sends both to the client. 7. Client decrypts logon session key using its password and stores the logon session key in cache. The client stores the TGT in cache.
- 52. •Access Service (Rememberthere is even more complexity) 1. User (client) encrypts the current time using the logon session key in cache creating an authenticator and sends the authenticator, the user’s KPN, the name of the target service (SPN), and the TGT to the TGS. 2. TGS decrypts the TGT using its shared key to access the logon session key. The logon session key is used to decrypt the authenticator and confirms the time is valid. 3. TGS extracts the user’s KPN from the TGT. TGS generates a service session key and encrypts the service session key using the logon session key. TGS uses server session key to generate service ticket and encrypts it using service’s password. 4. TGS sends service session key and the service ticket to the client.
- 53. •Access Service (Rememberthere is even more complexity) 5. Client decrypts service session key using cached logon session key, adds current time (as well as other items), and encrypts with the service session key to create an authenticator. 6. Client sends ticket and authenticator to remote server which runs service. 7. Service decrypts service ticket accessing the server session key and the KPN. Using the service session key, the service decrypts the authenticator and confirms the current time is valid. A Windows access token is generated 8. (Optional) If client requests mutual authentication, service encrypts current time using the service session key creating an authenticator and sends to the client. 9. Clients decrypts authenticator and validates time.
- 54. Troubleshooting Tools • Patience– Test methodically and • Knowledge - Know your Forests, Domains, Trusts, Functional Levels…get a basic lay of the land. • Always test from a different machine than the web server or domain controller! • SetSPN • Windows Security Logs • Windows 2008 ADUC • Kerbtray • Netmon and Fiddler • IIS Logs and IIS7 Failed Request Tracing • Kerberos Logging • Event Logging and/or Debug Logs
- 55. Common Issues thatbreak Kerberos • Times are out of sync – authenticators contain current time • Missing SPN • Duplicate SPN • SPN assigned to wrong service account • IIS Providers are incorrect (For IIS 5 or 6, see http://support.microsoft.com/kb/215383) • IIS 7 – remember Kernel mode authentication and check settings • Client TGT expired (7 days expiration – have user logon and logoff, no reboot required) • IE and non-default ports