Authentication. password-based authentication. address-based authentication. cryptographic protocols. passwords as keys.
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1 auth 1 Authentication password-based authentication address-based authentication cryptographic protocols passwords as keys eavesdropping trusted intermediaries session key establishment delegation
2 auth 2 Password proof by knowledge, sharing eavesdropping needed for dumb end systems cellular phone cloning single password across multiple hosts
3 auth 3 Password Guessing on-line: limit tries, delay, alarm off-line: dictionary attack f (p) capture 1. Your first, last, or kid s name 2. secret 3. stress-related words ( deadline, work ) 4. sports teams or terms ( bulls, golfer ) 5. payday 6. bonkers 7. The current season ( winter, spring ) 8. Your ethnic group
4 auth 4 9. repeated characters ( aaaaa, bbbbb ) 10. obscenities, sexual terms
5 auth 5 Storing Passwords per-node: /etc/passwd server: authentication storage server, retrieved by node (yp/nis) facilitator: server says yes/no need to authenticate node asking store hash only store encrypted with good, protected key but: needs to be in non-volatile memory (ROM?)
6 auth 6 Address-Based Authentication rcp, rsh:.rhosts node, user name per user reverse-lookup on IP address (in-addr.arpa) can use different login names /etc/hosts.equiv: trusted hosts
7 auth 7 Address-Based Authentication: Threats break in one, break in all A often: trusts B B, trusts A address spoofing; not easy for connections, but blind sending easy to listen/send on broadcast network MAC address spoofing prevention: filter on port, scramble Source routing to have T spoof A: ha; T; Di hd; T; Ai
8 auth 8 Humans and Computers humans: short, memorable key (8 characters, 48 bits) directly or as key for longer key (PGP, Netscape) computers: hidden key, directly
9 auth 9 Passwords as Keys directly as 56-bit key (e.g., use words) can t use for RSA p; q: use as seed for rng simulation-style rng, until primes found do once, then give offset hints to user
10 auth 10 Eavesdropping public key: need to secure Alice s private key use random challenge with signing difficult to protect against eavesdropping and disclosure Lamport, S/Key
11 auth 11 Trusted Intermediaries can t do pairwise authentication with secret keys: key explosion! Key Distribution Center (KDC) KDC knows all secrets ff asks KDC for secret (securely) to talk to any other fi node hand out session R key fffi : ticket single point of failure bottleneck
12 auth 12 Trusted Intermediaries: CA CA: ensure validity of public keys small number, preconfigured CA: single PoF CA: typically off-line, protected certificates are not sensitive compromised CA cannot eavesdrop need revocation list (CRL) must be signed and recent
13 auth 13 Multiple KDC Domains Secret keys: KDCs share pairwise key topology of KDC: tree with shortcuts Public keys: cross-certification of CAs example: Alice with CA A,BorisCA B Alice gets CA B s certificate signed by CA A Alice gets Boris certificate signed by CA B
14 auth 14 Session Key Establishment use public keys to authenticate, generate private key trade-off: processing, exposure limit lifetime limit replay attacks only need to expose short-term key to semi-trusted software
15 auth 15 Authorization authentication: identity (who) authorization: capability (what) may be implied (physical access) network: authentication access control list (ACL) groups: central server, signed certificate certificate: unwieldy, CRLs hierarchical groups typical: hiearchy(dh,director,...) andorganization
16 auth 16 Solaris ACLs setfacl -r -m user:czen:r-- file default entries per directory getfacl: # file: papers # owner: hgs # group: faculty user::rwx group::r-x group:irt:r-x mask:r-x other:--- #effective:r-x #effective:r-x
17 auth 17 Delegation short-term authorization for principals sign letter of authority (delegation) limit time, scope
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