1 / 18

Kerberos

James Johnson. Kerberos. What is it?. A system of authenticating securely over open networks Developed by MIT in 1983 Based on Needham-Schroeder Extended to fix vulnerabilities in Needham-Schroeder Currently widely used in industry ActiveDirectory. Why do I care?.

ima-hurst
Télécharger la présentation

Kerberos

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. James Johnson Kerberos

  2. What is it? • A system of authenticating securely over open networks • Developed by MIT in 1983 • Based on Needham-Schroeder • Extended to fix vulnerabilities in Needham-Schroeder • Currently widely used in industry • ActiveDirectory

  3. Why do I care? • Managing users across a huge network of computers is a pain • Individual users configured on each computer? LOL • Much easier to have a single authentication source • Kerberos provides this single source of authentication

  4. How Does It Work? • Clients authenticated using username and password • Single sign on • User authenticates username-password once per session • From then on, permissions granted using cryptographic “tickets”

  5. Cast of Characters • Principal (you) • Ticket Granting Service (TGS) • Key Distribution Center (KDC) • TGS and KDC separate entities on same host • Service Server (SS)

  6. Kerberos Authentication

  7. Messages (User Auth) • User -> Client: User, Pass • Keyuser = Hash(Password) • Client -> AS: User ID • AS->Client • Session key: {Sess}Keyuser • TGT: {Client ID, Client addr, validity period, Sess}Keyserver

  8. Messages (Service Auth) • Client -> TGS • {Client ID, Client addr, validity period, Sess}Keyserver , RequestedServiceID • Authenticator: {Client ID, Timestamp}Sess • TGS -> Client • Client-Server Ticket: {ClientID,Client addr, validitiy period, SessionClient-Server}Keyservice • {SessionClient-Server}Sess

  9. Messages (Service Request) • Client->Service • Client-Server Ticket • Authenticator: {Client ID,TimestampA} SessionClient-Server • Service->Client • {TimestampA+1} SessionClient-Server

  10. Domains/Realms • Kerberos designed to work across organizational boundaries • Each TGS constitutes a realm • Organizations can share “inter-realm keys” • Local AS issues TGT for remote TGS • Encrypted with inter-realm key • “Referral Ticket”

  11. Transitive Domain Referral

  12. Hierarchical Domains/Realms • Each realm shares a key with parent • Different key for each child • If no shared key between two realms, authentication path can be constructed

  13. Typical Implementations • MIT • Heimdal • Adds some functionality • Java • Microsoft Active Directory • Kerberos + LDAP + RPC • Does not use MIT software

  14. Security/Implementation Concerns • Synchronize clocks • NTP server • DO NOT USE KERBEROS 4 • Single point of failure • Harden servers • Consider redundancy of KDCs • One primary master, many secondary slaves • No automatic failover

  15. Kerberos + OpenLDAP • Kerberos can use LDAP backend instead of DB file • Eases DB replication and user management • Easy to do – Ubuntu packages, howtos

  16. Cross-Platform Integration • UNIX-only Kerberos networks are fairly straightforward • All use MIT software • Windows screws everything up • Tools for integrating Linux/BSD into AD • SAMBA • Likewise Open • Aspirin • SAMBA cannot act as a AD domain controller

  17. Conclusions • Kerberos greatly eases user management in Enterprise • Allows for fine-grained control • Inter-platform operation can be taxing

  18. Resources • http://technet.microsoft.com/en-us/library/bb742516.aspx • http://cryptnet.net/fdp/admin/kerby-infra/en/kerby-infra.html#overview • http://tools.ietf.org/html/rfc4120 • http://www.kerberos.org/events/2010conf/2010slides/2010kerberos_panel2.pdf

More Related