Theorie Practical part Outlook. Kerberos. Secure and efficient authentication and key distribution. Johannes Lötzsch and Meike Zehlike

Transcription

1 Secure and efficient authentication and key distribution October 27, 2009

2 Table of content Theorie Why to use SingleSignOn TGT ross-realm-authentication Practical part Setup your own -server kadmin (add principal, ktadd, list principals) klist, kinit, kdestroy SSH with SingleSignOn Outlook Further literature

3 Why to use Use cases for / Alternatives Trusted Instance for: Keydistribution Authentication SingleSignOn Trusted Third Party Alice Bob Well known alternative Trusted Third Parties: A in hierarchical PKI Asymmetric ryptography = slow / expensive Members of Web of Trust (e.g. PGP) Hard to say how trustworthy a Trustpath is

4 Why to use Use cases for / Alternatives Trusted Instance for: Keydistribution Authentication SingleSignOn Trusted Third Party Alice Bob Well known alternative Trusted Third Parties: A in hierarchical PKI Asymmetric ryptography = slow / expensive Members of Web of Trust (e.g. PGP) Hard to say how trustworthy a Trustpath is

5 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) Authentication Server (AS) lient () erifier () Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

6 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

7 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

8 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

9 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

10 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

11 Based on symmetric Needham-Schroeder-Protocol Assumption: Each participant exchanged Key with AS on save channel (K AS,, K AS, ) AS Procedure: 1. Authentication Request: (,, time exp, n) 2. Authentication Reply: E KAS, (, time exp, n, K, ), E KAS, (, time exp, K, ) 3. Application Request: E KAS, (, time exp, K, ), E K, (ts, K subsession, ck) 4. Application Reply: E K, (ts)

12 SingleSignOn TGT Ticket Granting Tickets K AS, needs to be handled with caution usage from different machines should not be stored on clients = always created from a password Howto cache credentials? 1-2: Authentication with AS using password = TGT 3-4: Authentication with TGS using TGT = SessionTicket for 5-6: Authentication with using SessionTicket 3-6 can be repeated until time exp of TGT

13 SingleSignOn TGT Ticket Granting Tickets K AS, needs to be handled with caution usage from different machines should not be stored on clients = always created from a password Howto cache credentials? TGS 3 4 AS : Authentication with AS using password = TGT 3-4: Authentication with TGS using TGT = SessionTicket for 5-6: Authentication with using SessionTicket 3-6 can be repeated until time exp of TGT

14 SingleSignOn TGT Ticket Granting Tickets K AS, needs to be handled with caution usage from different machines should not be stored on clients = always created from a password Howto cache credentials? TGS 3 4 AS : Authentication with AS using password = TGT 3-4: Authentication with TGS using TGT = SessionTicket for 5-6: Authentication with using SessionTicket 3-6 can be repeated until time exp of TGT

15 SingleSignOn TGT Ticket Granting Tickets K AS, needs to be handled with caution usage from different machines should not be stored on clients = always created from a password Howto cache credentials? TGS 3 4 AS : Authentication with AS using password = TGT 3-4: Authentication with TGS using TGT = SessionTicket for 5-6: Authentication with using SessionTicket 3-6 can be repeated until time exp of TGT

16 SingleSignOn TGT Ticket Granting Tickets K AS, needs to be handled with caution usage from different machines should not be stored on clients = always created from a password Howto cache credentials? TGS 3 4 AS : Authentication with AS using password = TGT 3-4: Authentication with TGS using TGT = SessionTicket for 5-6: Authentication with using SessionTicket 3-6 can be repeated until time exp of TGT

17 ross-realm-authentication ross-realm-authentication Realm1 Realm2 TGS1 AS1 TGS2 AS2

18 ross-realm-authentication ross-realm-authentication Realm1 Realm2 TGS1 AS1 TGS2 AS2

19 ross-realm-authentication Authentication in hierarchic Realms Parent-Realm TGS0 AS0 Realm1 Realm2 TGS1 AS1 TGS2 AS2

20 ross-realm-authentication Authentication in hierarchic Realms Parent-Realm TGS0 AS0 Realm1 Realm2 TGS1 AS1 TGS2 AS2

21 ross-realm-authentication Authentication in hierarchic Realms Parent-Realm TGS0 AS0 Realm1 Realm2 TGS1 AS1 TGS2 AS2

22 ross-realm-authentication Authentication in hierarchic Realms Parent-Realm TGS0 AS0 Realm1 Realm2 TGS1 AS1 TGS2 AS2

23 Setup your own -server Installation on Debian / Ubuntu $ wget krb.sh... read, UNDERSTAND, modify... $ chmod +x setup krb.sh $ sudo./setup krb.sh

24 kadmin (add principal, ktadd, list principals) Add new user (create K AS, ) $ sudo kadmin.local kadmin.local: addprinc newuser Enter password for principal [email protected] : $passwort Re-enter password for principal [email protected] : $passwort Principal [email protected] created. kadmin.local: list principals... [email protected]...

25 kadmin (add principal, ktadd, list principals) Add new server (create K TGS, ) kadmin.local: addprinc -randkey host/servername.example.com Principal host/[email protected] created. kadmin.local: ktadd -k /tmp/key host/servername.example.com Entry for principal host/servername.example.com with kvno 3, encryption type AES-256 TS mode with 96-bit SHA-1 HMA added to keytab WRFILE:/tmp/key. $ sudo scp /tmp/key [email protected]:/etc/krb5.keytab

26 klist, kinit, kdestroy Obtaining the TGT $ kinit newuser Password for [email protected]: $passwort $ klist -5 Ticket cache: FILE:/tmp/krb5cc 1000 Default principal: [email protected] alid starting Expires Service principal 10/07/09 20:16:04 10/08/09 06:16:04 krbtgt/[email protected] renew until 10/08/09 20:15:58 $ kdestroy $ klist -5 klist: No credentials cache found (ticket cache FILE:/tmp/krb5cc 1000)

27 SSH with SingleSignOn Use the -principal for SSH $ yes sudo adduser --disabled-password newuser $ kdestroy $ ssh [email protected] [email protected] s password: passwort is disabled Permission denied, please try again. $ kinit newuser $ Password for [email protected]: $passwort $ ssh [email protected] [email protected]: $

28 SSH with SingleSignOn Done SingleSignOn works $ klist -5 Ticket cache: FILE:/tmp/krb5cc 1000 Default principal: [email protected] alid starting Expires Service principal 10/07/09 20:27:09 10/08/09 06:27:09 krbtgt/[email protected] renew until 10/08/09 20:27:03 10/07/09 20:27:14 10/08/09 06:27:09 host/[email protected] renew until 10/08/09 20:27:03 $ ssh [email protected] [email protected]: $ exit $ ssh [email protected] [email protected]: $ $ kdestroy

29 Further literature Further literature DIY (protocol)