9-1©2007 Raj JainCSE571SWashington University in St. LouisOverview of Overview of Authentication SystemsAuthentication SystemsRaj Jain Washington University in Saint LouisSaint Louis, MO [email protected]/Video recordings of this lecture are available at:http://www.cse.wustl.edu/~jain/cse571-07/9-2©2007 Raj JainCSE571SWashington University in St. LouisOverviewOverview! Passwords! Address based authentication! Key Distribution Center (KDC)! Certification Authorities (CAs)! Multiple Trust Domains! Session Keys! Delegation9-3©2007 Raj JainCSE571SWashington University in St. LouisPasswordsPasswords! Do not store passwords in clear. Store hashes.⇒ Subject to offline attack! Encrypt the hash storage.⇒ Where do you keep the master key?! Do not transmit passwords in clear.! Use password as a key to encrypt a challenge.⇒ Cryptographic Authentication9-4©2007 Raj JainCSE571SWashington University in St. LouisAddress based authenticationAddress based authentication! /etc/hosts.equiv file in UNIX.! John Smith can do on B whatever he is allowed to do on A.⇒ Users need to have the same name on all machines.! Per user .rhosts files. Lists <address, remote account name> that can access this account.! Issue: Attacker can gain access to all machines! Attacker can change IP addresses of machines and can access remote resources of all users on that machine.! Attacker can use source route <A, X, D> to send messages to D (from A).9-5©2007 Raj JainCSE571SWashington University in St. LouisMachine vs. Person AuthenticationMachine vs. Person Authentication! Machines can store long secret keys.! Person's password can be used to decrypt a long secret key or private key.9-6©2007 Raj JainCSE571SWashington University in St. LouisSecret Keys for an NSecret Keys for an N--System NetworkSystem Network! n system need n(n-1)/2 pairs of secret keys! Each system remembers n-1 keys.! If a new system comes in n new key are generated.! If a system leaves, n-1 keys are removed.ABDCEF9-7©2007 Raj JainCSE571SWashington University in St. LouisKey Distribution Center (KDC)Key Distribution Center (KDC)! Each node is configured with KDC's key! KDC has all the keys.! KDC sends a key encrypted with A's key and B's key to A.! Issues:" If KDC is compromised, all systems are compromised." KDC is single point of failure or performance bottleneck." KDC has to be on-line all the time.ABDCEFKDC9-8©2007 Raj JainCSE571SWashington University in St. LouisCertification Authorities (CAs)Certification Authorities (CAs)! Unsigned public keys can be tampered.! Public Keys are signed by CAs ⇒ Certificates.! Each system is configured with CA's public key.! CA's don't have to be on-line.! A compromised CA cannot decrypt conversations.9-9©2007 Raj JainCSE571SWashington University in St. LouisCertificate Revocations Lists (CRL)Certificate Revocations Lists (CRL)! The lists are published regularly.! Certificates are checked in a recent CRL.! Certificate contains user's name, public key, expiration time, a serial number, and CA's signature on the content.9-10©2007 Raj JainCSE571SWashington University in St. LouisKDCs in Multiple Trust DomainsKDCs in Multiple Trust Domains9-11©2007 Raj JainCSE571SWashington University in St. LouisKDCs in Multiple Trust Domains (Cont)KDCs in Multiple Trust Domains (Cont)! Issue: Every pair of KDC needs a shared key ⇒ KDC hierarchy! Issue: Every pair of KDC needs a shared key ⇒ KDC hierarchy! Some pairs of KDCs have a secret key9-12©2007 Raj JainCSE571SWashington University in St. LouisCA's in Multiple DomainsCA's in Multiple Domains! Each CA has a certificate from the other.! Alice with Boris's certificate and Boris's CA's certificate issued by Alice's CA can authenticate BorisAliceCAAliceBorisCABorish9-13©2007 Raj JainCSE571SWashington University in St. LouisSession KeysSession Keys! Public key is used to exchange a secret key.! Each session should start with a new secret key.9-14©2007 Raj JainCSE571SWashington University in St. LouisDelegationDelegation! Authentication forwarding! A signed message with time limit and details of privileges9-15©2007 Raj JainCSE571SWashington University in St. LouisSummarySummary! Passwords should not be stored or transmitted in clear ⇒ Use to generate keys! Address based authentication is not safe.! Key Distribution Center (KDC): Single point of failure! Certification Authorities (CAs) sign public keys.! Multiple Trust Domains: Hierarchy of KDCs or CAs9-16©2007 Raj JainCSE571SWashington University in St. LouisHomework 9Homework 9! Read Chapter 9 of the textbook! Submit answers to Exercise 9.3! Extend the scenario in Section 9.7.4.1 Multiple KDC Domains to a chain of three KDCs. In other words assume that Alice wants to talk to Boris through a chain of three KDCs (Alice’s KDC, A KDC that has shared keys with both Alice’s KDC and Boris’s KDC and finally, Boris’s KDC). Give the sequence of events necessary to establish
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