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KERBEROS

KERBEROS. Miah , Md. Saef Ullah . What Is Kerberos?. An authentication Service, designed for using in a distributed networked environment. Developed at MIT in mid 1980s Named after a Greek mythological creature named “Cerberus”, a three headed dog. Why Kerberos. Secure

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KERBEROS

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  1. KERBEROS Miah, Md. Saef Ullah

  2. What Is Kerberos? • An authentication Service, designed for using in a distributed networked environment. • Developed at MIT in mid 1980s • Named after a Greek mythological creature named “Cerberus”, a three headed dog.

  3. Why Kerberos • Secure • An opponent does not find it to be the weak link • Reliable • The system should be able to back up another • Transparent • An user should not be aware of authentication • Scalable • The system supports large number of clients and severs

  4. Cryptography Approach • Private Key: Each party uses the same secret key to encode and decode messages. • Uses a trusted third party which can guaranty for the identity of both parties in a transaction. Security of third party is imperative.

  5. How Kerberos Works • Instead of client sending password to application server: • Request Ticket from authentication server • Ticket and encrypted request sent to application server • Ticket contains Id of client, Network Address of Client and Id of server and secret encryption key shared by Application server and Authentication server.

  6. How Kerberos Works

  7. How Kerberos works?Ticket Granting Tickets C → AS: IDc || IDtgs || TS1 AS → C: E Kc [Kc,tgs|| IDtgs || TS2 || Lifetime2 || Tickettgs] Tickettgs = E Ktgs[Kc,tgs || IDC || ADC || IDtgs || TS2 || Lifetime2]

  8. How Kerberos Works?The Ticket Granting Service C → TGS: IDS || Tickettgs || AuthenticatorC TGS → C: EKc,tgs[ KC,S || IDS || TS4 || TicketS ] Ticket tgs = EKtgs[ KC,tgs || IDC || ADC || IDtgs || TS2 || Lifetime2 ] Ticket S = EKS [ KC,S || IDC || ADC || IDs || TS4 || Lifetime4 ] Authenticator C = E Kc, tgs[ IDC || ADC || TS3 ]

  9. How Kerberos works?The Application Server C → S: TicketS || AuthenticatorC S → C: EKc,s[ TS5 + 1 ] TicketS = EKs[ KC,S || IDC || ADC || IDs || TS4 || Lifetime4 ] AuthenticatorC = EKc, s[ IDC || ADC || TS5 ]

  10. Multiple Kerberi

  11. Multiple Kerberi (contd..) C -> AS: IDc||IDtgs||TS1 AS -> C: EKc[Kc,tgs||IDtgs||TS2||Lifetime2||Tickettgs] C -> TGS: IDtgsrem||Tickettgs||Authenticatorc TGS -> C: EKc,tgs[Kc,tgsrem||IDtgsrem||TS4||Lifetime2||Tickettgsrem] C -> TGSrem: IDsrem|| Tickettgsrem|| Authenticatorc TGSrem -> C: EKc,tgsrem[Kc,srem||IDsrem||TS6|| Ticketsrem] C -> Srem: Ticketsrem|| Authenticatorc

  12. KERBEROS Version 5 versus Version4 • Environmental shortcomings of Version 4: • Encryption system dependence: DES • Internet protocol dependence • Ticket lifetime • Authentication forwarding • Inter-realm authentication • Technical deficiencies of Version 4: • Double encryption • Session Keys • Password attack

  13. New Elements in Kerberos Version 5 • Realm • Indicates realm of the user • Options • Times • From: the desired start time for the ticket • Till: the requested expiration time • Rtime: requested renew-till time • Nonce • A random value to assure the response is fresh

  14. Weaknesses and Solutions

  15. References • Cryptography and Network Security by William Stallings • http://www.obscure.org/~jafitz/250_p1/kerberos.htm • http://en.wikipedia.org/wiki/Kerberos_(protocol) • www.cs.purdue.edu/homes/bertino/426Fall2009

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