Kerberos

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Network protocol, history, uses, application, procedures

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  • Client/TGS Session Key - encrypted with Client Secret Keyb. Ticket Granting Ticket - includes Client ID, client network address, ticket validity period, and Client/TGS Session key - encrypted with TGS secret Key
  • C. Ticket Granting Ticket from B - (encrypted with TGS Secret key) + File service IDD. Authenticator - composed of Client ID and Timestamp - encrypted with Client/TGS session key from ATGS decrypts C and gets Ticket Granting Ticket - includes Client ID, Client network address, ticket validity period, and Client/TGS Session Key
  • E. Client-to-FS ticket - Client ID, network Address, Validity period, Client/Server secret key - encrypted with FS Secret keyf. Client/Server Session Key - encrypted with client/TGS session key from A
  • E. Client-to-FS ticket - Client ID, network Address, Validity period, Client/Server secret key - encrypted with FS Secret keyG. Authenticator - composed of Client ID and Timestamp - encrypted with Client/SERVER session key from FFS decrypts E using FS secret key and gets Client ID, network address, validity period, Client/Server session keyFS decrypts G using Client/Server Session Key and gets Client ID and timestamp
  • Server sends the following message to client to confirm its true identity and willingness to serve the clientClient decrypts H using client/server session key, checks if timestamp is timestamp + 1, if so, it is correctly updated, client can trust the FS
  • Server sends the following message to client to confirm its true identity and willingness to serve the clientClient decrypts H using client/server session key, checks if timestamp is timestamp + 1, if so, it is correctly updated, client can trust the FS
  • Kerberos

    1. 1. Third Party AuthentiStrong Cryptograph
    2. 2. Modern HistoryMassachusettssInstitute ofTechnologyProject AthenaSteve Millerand CliffordNeuman
    3. 3. evolutionEarly Kerberos (v1, v2, v3)Kerberos 4Kerberos 5
    4. 4. BASIC DESIGNAuthentication ServerTicket Granting ServerFile ServerKey Distribution CenterCLIENT
    5. 5. BASIC DESIGNASTGSFSCLIENTUserName: gichyPassword: 12345?><Client Secret KeyOne way Hash
    6. 6. BASIC DESIGNASTGSFSCLIENTUser gichy wants touse file server(clear text)
    7. 7. BASIC DESIGNASTGSFSCLIENTChecks ifclient is inthe databaseGeneratesthe ClientSecret Key
    8. 8. BASIC DESIGNASTGSFSCLIENT2 Messagesbeing sentA. Client / TGSSession KeyB. TicketGranting TicketClient decodes A:Using its secretkeyClient CAN’Tdecode B
    9. 9. BASIC DESIGNASTGSFSCLIENTC. TicketGranting Ticketfrom BD.AuthenticatorTGS decrypts Cand gets TicketGranting TicketTGS decrypts DusingClient/TGSSession key andgets Client IDand TimestampTGS checks thatClient ID from Cmatches Client IDfrom D andtimestamp doesnot exceed ticketvalidity period
    10. 10. BASIC DESIGNASTGSFSCLIENTE. Client-to-FSticketF. Client/ServerSession KeyClient decodes Fusing Client/TGSsession key,obtainsClient/ServerSession Key
    11. 11. BASIC DESIGNASTGSFSCLIENTE. Client-to-FSticketG.AuthenticatorFS decrypts EFS decrypts GFS checks thatClient ID from Ematches Client IDfrom G andtimestamp doesnot exceed validityperiod
    12. 12. BASIC DESIGNASTGSFSCLIENTH. Thetimestampfound in G + Iencrypted withtheClient/ServerSession KeyClient decryptsH
    13. 13. BASIC DESIGNASTGSFSCLIENTClient issuesservice requestto the FSFS services therequest
    14. 14. hank You

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