This document provides an overview and guide to Kerberos authentication. It begins with introductions and an agenda. The agenda covers Kerberos overview, the logon process, accessing a website, troubleshooting Kerberos, and delegation. It then discusses Kerberos details such as dependencies, service principal names, and references. It concludes with a Q&A section and appendix.

1. Kerberos Survival GuidePresented by:JD WadeSenior SharePoint Consultant, MCTS, MCITPMail: jd.wade@hrizns.comBlog: http://wadingthrough.comLinkedIn: JD WadeTwitter: http://twitter.com/JDWade

2. Who is JD Wade?SharePoint Consultant since 2007

3. Certified KnowledgeLake Partner

4. With Horizons since 2005

5. Member of SharePoint 2007 and 2010 TAP

6. Over 10 years of IT experience

7. Technical Editor for book SharePoint 2010 Disaster Recovery http://tinyurl.com/SPDRBook2010

8. Loves anything related to sound

9. Probably has one of the driest senses of humor in the roomAgendaOverview

10. Logon Process

11. Accessing a Web Site

12. Troubleshooting Kerberos

13. DelegationKerberosMassachusetts Institute of Technology

14. Details Out of ScopeRenewing tickets

15. Ticket expiration

16. Keys

17. Authenticator

18. TGT Structure

19. Service Ticket Structure

20. Encryption/Decryption

21. Multiple domains/forests

22. DependenciesSPN

24. Service Principal NameService ClassHost NamePortHTTP/website:80

25. Service Classes allowed by hostalerterhttppolicyagentscmappmgmtiasprotectedstorageseclogonbrowseriisadrasmansnmpcifsminremoteaccessspoolercisvcmessengerreplicatorTapisrv clipsrvmsiserverrpctimedcommcsvcrpclocatortrksvrdhcpnetdderpcsstrkwksdmservernetddedsmrsvpupsdnsnetlogonsamssw3svcdnscachenetmanscardsvrwinseventlognmagentscesrvwwweventsystemoakleySchedulefaxplugplay

26. KerberosBenefits

27. Delegated Authentication

28. Interoperability

29. More Efficient Authentication

30. Mutual Authentication

31. IIS – Chatty by default

32. IIS6 – See MS KB 917557

33. IIS7 – See MS KB 958473Logon Process

34. KDC

35. KDC

36. KDCSPN

37. KDC

38. Access Web Site

39. 401

40. SPN

42. <system.webServer> <security> <authentication> <windowsAuthentication enabled="true" useAppPoolCredentials="true" /> </authentication> </security></system.webServer>

44. TroubleshootingKerberos

45. ToolsKnowledge

46. SetSPN

47. Windows Security Logs

48. Windows 2008 ADUC or ADSIEdit

49. Kerbtray or Klist

50. Netmon and Fiddler

51. IIS Logs and IIS7 Failed Request Tracing

52. LDP

53. Kerberos Logging

54. Event Logging and/or Debug LogsCommon Issues that break KerberosTimes are out of sync – authenticators contain current time

55. Missing SPN

56. Duplicate SPN

57. SPN assigned to wrong service account

58. IIS Providers are incorrect (For IIS 5 or 6, see http://support.microsoft.com/kb/215383)

59. IIS 7 – remember Kernel mode authentication and check settings

60. Client TGT expired (7 days expiration – have user logon and logoff, no reboot required)

61. IE and non-default portsDelegation

64. FBAKerberos

67. ReferencesKen Schaefer’s Multi-Part Kerberos Blog Posts:http://www.adopenstatic.com/cs/blogs/ken/archive/2006/10/20/512.aspx

68. What Is Kerberos Authentication?http://technet.microsoft.com/en-us/library/cc780469%28WS.10%29.aspx

69. How the Kerberos Version 5 Authentication Protocol Workshttp://technet.microsoft.com/en-us/library/cc772815%28WS.10%29.aspx

70. Explained: Windows Authentication in ASP.NET 2.0http://msdn.microsoft.com/en-us/library/ff647076.aspxReferencesKerberos Authentication Tools and Settingshttp://technet.microsoft.com/en-us/library/cc738673%28WS.10%29.aspx

71. How To: Use Protocol Transition and Constrained Delegation in ASP.NET 2.0http://msdn.microsoft.com/en-us/library/ff649317.aspx

72. Spence Harbar’s Bloghttp://www.harbar.netQ & A

73. Appendix

74. Kerberos is an open authentication protocol. Kerberos v5 was invented in 1993 at MIT.

75. Authentication is the process of proving your identity to a remote system.

76. 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.

77. 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.

78. Service password is encrypted as the service key.

79. KDCs are found through a DNS query. Service registered in DNS by DCs.Showing detail behind what is happening inside of KDC but for day-to-day, use can just remember KDC

80. Another reason for simplification: encryption upon encryption upon encryption…just remember it is encrypted

81. This is a Windows-centric Kerberos presentation

82. Load balanced solutions need service account

83. All web applications hosted using the same SPN have to be hosted with the same account

84. Use A records, not CNAME recordsTerms

85. Key Distribution Center (KDC) – In Windows AD, KDC lives on domain controllers (DC), KDCs share a long term key across all DCs.

86. KDC security account database – In Windows, it is Active Directory

87. Authorization Service (AS) – part of the KDC

88. Ticket Granting Service (TGS) – part of the KDC

89. 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.TicketsTicket Granting Ticket (TGT)

90. A user's initial ticket from the authentication service

91. Used to request service tickets

92. Meant only for use by the ticket-granting service.

93. Service ticket for the KDC (service class = krbtgt)

94. Service Ticket

95. Enables the ticket-granting service (TGS) to safely transport the requester's credentials to the target server or service.ToolsKnowledge

96. SetSPN

97. Windows Security Logs

98. Windows 2008 ADUC or ADSIEdit

99. Kerbtray or Klist

100. Netmon and Fiddler

101. IIS Logs and IIS7 Failed Request Tracing

102. LDP

103. Kerberos Logging

104. Event Logging and/or Debug LogsTroubleshooting

105. 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.

106. Remember that authenticators contain the current time. Check for time sync issues.Request TGT (Remember there is even more complexity)User (client) logs into workstation entering their password.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.Client sends these three items to the KDC.KDC get user’s password from AD, decrypts time and verifies it is valid.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).

107. Request TGT (Remember there is even more complexity)KDC sends both to the client.Client decrypts logon session key using its password and stores the logon session key in cache. The client stores the TGT in cache.

108. Access Service (Remember there is even more complexity)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.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. 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.TGS sends service session key and the service ticket to the client.

109. Access Service (Remember there is even more complexity)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.Client sends ticket and authenticator to remote server which runs service. 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(Optional) If client requests mutual authentication, service encrypts current time using the service session key creating an authenticator and sends to the client.Clients decrypts authenticator and validates time.

110. Troubleshooting ToolsPatience – Test methodically and

111. Knowledge - Know your Forests, Domains, Trusts, Functional Levels…get a basic lay of the land.

112. Always test from a different machine than the web server or domain controller!

113. SetSPN

114. Windows Security Logs

115. Windows 2008 ADUC

116. Kerbtray

117. Netmon and Fiddler

118. IIS Logs and IIS7 Failed Request Tracing

119. Kerberos Logging

120. Event Logging and/or Debug LogsCommon Issues that break KerberosTimes are out of sync – authenticators contain current time

121. Missing SPN

122. Duplicate SPN

123. SPN assigned to wrong service account

124. IIS Providers are incorrect (For IIS 5 or 6, see http://support.microsoft.com/kb/215383)

125. IIS 7 – remember Kernel mode authentication and check settings

126. Client TGT expired (7 days expiration – have user logon and logoff, no reboot required)

127. IE and non-default ports