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Kerberos

Kerberos. 그리스 신화에서 저승의 신 하데스의 문을 지키는 머리가 셋 달린 개 MIT 의 Project Athena 팀에 의해 개발된 인증 (authentication) 서비스 커버로스는 제 3 의 인증서버를 이용해 사용자간에 인증 , 즉 , 신분의 확인을 인증서버를 통해 하는 것. Server Access Request. Service Ticket. Session key, Ticket. authentication. Service Request. Unique Key.

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Kerberos

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  1. Kerberos • 그리스 신화에서 저승의 신 하데스의 문을 지키는 머리가 셋 달린 개 • MIT의 Project Athena 팀에 의해 개발된 인증(authentication) 서비스 • 커버로스는 제 3의 인증서버를 이용해 사용자간에 인증, 즉, 신분의 확인을 인증서버를 통해 하는 것

  2. Server Access Request Service Ticket Session key, Ticket authentication Service Request Unique Key Session Key Access to Services and Servers • 사용자는 Kerberos Server 에서 인증 받음 • 인증 후, Ticket-Granting Server에 서버 접근 권한 요청 • 얻어낸 Service Ticket을 이용하여 해당 서버에 접근 User U Ticket-Granting Server Kerberos Server Other Server

  3. Kerberos • 4 entities in Kerberos • U (User): A서버에 접근하려 함 • KS (Kerberos Server): 사용자 인증 후, ticket 발행 • TGS (Ticket-Granting Server): ticket 검사 후 A서버에 접근을 허용하는 ticket 발행 • S (Server): A서버 (e.g., 파일 서버, …) • Ticket in Kerberos • Authenticated token • Unforgeable, nonreplayable, authenticated object

  4. Kerberos 인증 구성요소 • Password • 사용자 U의 패스워드. KS(커버로스서버) 에 저장 • KKS,TGS • KS (커버로스)서버와 TGS (티켓 그랜팅)서버 간의 비밀 키 • KTGS,S • TGS 서버와 서버 S 간의 비밀 키

  5. User U Ticket-Granting Server Encrypted Under Password 2. Session Key (SG), Ticket (TG) 2. Session Key (SG) Encrypted Under KKS,TGS 1. U’s Identity Kerberos Server Kerberos Session 의 초기화 • 사용자의 ID를 Kerberos Server에 전달 • Kerberos Server는 Session Key(S)와 Ticket(TG)를 사용자에 전달하면서, Ticket Granting Server에 Session Key(S)를 등록

  6. Encrypted Under SG 1. Request to Access Server A User U Ticket-Granting Server 2. Ticket to A Server to Access Server A, SA (Encrypted Under KTGS,S), SA Encrypted Under SG Kerberos 티켓 전달 • 초기화 과정에서 얻어낸 Session Key(SG) 와 Ticket(TG) 를 이용하여 Ticket-Granting Server 에 ‘파일 접근 티켓’ 요청 • Ticket-Granting Server가 ‘파일 접근 티켓’을 사용자에게 전달 • ticket contains U’ id, A’s id, access rights, session key SA, expiration date

  7. Kerberos 의 장점 • No Password communicated in the network • Protection against spoofing • Limited period of validity(8hrs) • Timestamps to prevent replay attacks • Mutual authentication

  8. Kerberos 의 단점 • Requires continuous availability of a trusted TGS • Authenticity of servers requires a trusted relationship between the TGS and every server • Requires timely transactions

  9. Authentication Server (AS) Client Ticket Granting Server (TG) Application Server Kerberos • Kerberos System from MIT • Trusted Third-Party stores all the passwords KERBEROS User Logon Ticket Granting Ticket Ticket Granting Ticket Service Granting Ticket Service Granting Ticket Service for the Client

  10. Authentication Server Client Ticket Granting Server (TG) Application Server (AS) Kerberos ID = ‘Alice’ Alice, Password Alice’s Password => K{Alice} Ticket-granting Ticket = EK1 ( ‘Alice’, K{Alice-TG} ) EK{Alice} ( K{Alice-TG}, Ticket-granting Ticket ) Service-granting Ticket EK{Alice-AS} ( Timestamp ) Ticket-granting Ticket EK {Alice-TG} ( Timestamp ) Ticket-granting Ticket Service-granting Ticket = EK2( ‘Alice’, K{Alice-AS}, ..) EK{Alice-TG} (K{Alice-AS}, Service-granting Ticket )

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