Active Directory and NT Kerberos

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Active Directory and NT Kerberos

• Rooster
• JD Glaser

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Introduction to NT Kerberos v5

• What is NT Kerberos?
• How is it different from NTLM
• NT Kerberos vs MIT Kerberos
• Delegation and Client Authentication
• What does NT Kerberos look like on the wire?
• KTNet - A native NT Kerberos telnet server

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What is NT Kerberos

• NTs new authentication system
• MIT Kerberos v5 - an Open Standard
• Kerberos is the default authenticator in W2K
  domains
• NTLM still used for compatibility
• usually the weakest version

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How is it different from NTLM

• Doesnt use a password hash system
• Requires fewer authentication calls
• More sophisticated - Yes
• More secure? - Possibly in pure mode
• Backwards compatibility hinders it
• NTLM v2 is strong in pure mode as well

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NT Kerberos

• Integrated with platform
• Locates KDC via DNS - DNS server required for
  install
• No support for DCE style cross-realm trust
• No raw krb5 API
• Postdated tickets (not implemented)
• Uses authdata field in ticket

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Windows 2000 Kerberos standards

• RFC-1510
• Kerberos change password protocol Kerberos set
  password protocolRC4-HMAC Kerberos Encryption
  type
• PKINIT

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Kerberos Interoperability Scenarios

• Kerberos clients in a Win2000 domain
• Kerberos servers in a Win2000 domain
• Standalone Win2000 systems in a Kerberos realm
• Using a Kerberos realm as a resource domain
• Using a Kerberos realm as an account domain

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MIT Kerberos Differences

• Win2000
• Clients
• Just logon
• Just logoff
• Domain membership
• Example app everything
• Servers
• Use computer account via SCM

• MIT
• Clients
• User logon with kinit
• User logoff with kdestroy
• Configured with /etc/krb5.conf
• Example app telnet
• Servers
• Do not logon use saved keys from keytab

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Using Kerberos clients

• Customer wants to have its non-windows Kerberos
  users use their Win2000 accounts

nt.company.com

• Setup the /etc/krb5.conf
• Users kinit with their Win2000 account

Unix workstation
Windows 2000 Server
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Using Kerberos servers

• Customer wants to user their Kerberos enabled
  database server in an n-tier application
  front-ended by IIS

nt.company.com

• /etc/krb5.conf on database server
• Create service account in domain
• Use ktpass to export a keytab
• Copy keytab to database server
• IIS server is trusted for delegation

Windows 2000 Wks
Windows 2000 IIS Server
Unix Database Server
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Kerberos realm as an account domain

• User logon with Kerberos principal
• User has shadow account in an account domain (for
  applying authz)
• Mapping is used at logon for domain identity

Domain trusts realm users
user_at_win2k.domain.com (user_at_MIT.REALM.COM)
comp_at_win2k.domain.com
User_at_MIT.REALM.COM
win2k.domain.com
MIT.REALM.COM
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Standalone Win2000 computers

• An employee has a Win2000 computer that they want
  to use in a Kerberos realm

MIT.REALM.COM

• Configure system as standalone (no domain)
• Use Ksetup to configure the realm
• Use Ksetup to establish the local account mapping
• Logon to Kerberos realm

Linux/Unix
Win2000
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Trusting a Kerberos realm

• Win2000 users accessing services in Kerberos
  realms
• Kerberos users accessing services in domains

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Windows 2000 Domain Trusts
Explicit Kerberos trust
microsoft.com
Kerberos realm
Domain
fareast. microsoft. com
europe. microsoft. com
Explicit Windows NT 4.0-style trust
Domain
Domain
Domain
Domain
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Cross-domain Authentication
company.com
west.company.com
east.company.com
KDC
KDC
srv1.east.company.com
Windows 2000 Professional
Windows 2000 Server
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Using Unix KDCs withWindows 2000 Authorization
COMPANY.REALM
nt.company.com
MITKDC
Windows 2000KDC
Name Mapping to NT account
Windows 2000 Server
Win2000 Professional
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NT Kerberos vs MIT Kerberos

• NT caches the password for ticket renewal
• Its not certain whether NT uses ticket caching
  tracking stolen replay tickets

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Kerberos v5 Ticket Details
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Delegation and Client Authentication
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NT Kerberos On The Wire
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Thank you

• Rooster, rooster_at_attrition.org
• JD Glaser, jd.glaser_at_foundstone.com

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Appendix

• John Brezak, PM - Microsoft
• Kerberos Talk - MTB 99