Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Advanced Operating Systems Lecture notes Dr. Clifford Neuman Dr. Dongho Kim University of Southern California Information Sciences Institute

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Focus on Authorization Focusing on authorization and the management of policies used in the authorization decision. –Not really new - this is a reference monitor. –Applications shouldn’t care about authentication or identity. ▪Separate policy from mechanism –Authorization may be easier to integrate with applications. –Hide the calls to the key management and authentication functions.

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Generic Authorization and Access-control API Allows applications to use the security infrastructure to implement security policies. gaa_get_object_eacl function called before other GAA API routines which require a handle to object EACL to identify EACLs on which to operate. Can interpret existing policy databases. gaa_check_authorization function tells application whether requested operation is authorized, or if additional application specific checks are required Application GAA API input output gaa_get_ object_eacl gaa_check_ authorization Yes,no,maybe SC,obj_id,op

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Credential transport (needed) The GAA-API gets user & connection info from Security Context: Evaluated and unevaluated credentials Delegated authority Cross-calls to transport to retrieve additional creds The security context is provided as: –Output from GSS-API (requires many calls) –Credentials from transport or session protocols –SSL, ARDP –Other extensions are needed: –IPSec, pulled from Kernel, other extensions

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Evaluation of credentials POLICY gaa_get_object_eacl gaa_check_authorization GAA API App EACL... GAA API Security Context GSS-API LIBRARY Transport Mechanism a 6a a 6b

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Integrating security services The GAA-API calls must be made by applications. –This is a major undertaking, but one which must be done no matter how one chooses to do authorization. These calls are at the control points in the app –They occur at auditable events, and this is where records should be generated for ID systems –They occur at the places where one needs to consider dynamic network threat conditions. –Adaptive policies use such information from ID systems. –They occur at the right point for billable events.

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Electronic commerce Some authorization policies do not require user authentication at all - just that an item is paid for. –Policy specifies required payment. –Cross call to credential transport retrieves payment credentials and grants access. –If application used GAA-API, no change to the application is necessary, simply specify the payment policy instead of a more traditional identity based policy.

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE ID and Audit relation to GAA-API SECURITY AUDIT RECORDS THREAT CONDITION UNDER ATTACK POLICY gaa_get_object_eacl gaa_check_authorization GAA API App EACL... GAA API Security Context GSS-API LIBRARY Transport Mechanism a 6a a 6b

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Application based ID Without the GAA-API –Convince each application developer to add calls to audit functions in addition to all the other security calls they make (good luck). Of course it needs to do authentication too. With the GAA-API –Get developers to use the GAA for authorization decisions instead of making multiple calls to implement their own authorization database. –Create module for GAA implementation that generates audit records according to policy. –Write policy (inc. adaptive or credential based) that says when to generate audit records.

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE CSci555: Advanced Operating Systems Lecture 7 - October 10 and 11, 2002 Security Architecture Dr. Clifford Neuman University of Southern California Information Sciences Institute

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Key distribution Conventional cryptography –Single key shared by both parties Public Key cryptography –Public key published to world –Private key known only by owner Third party certifies or distributes keys –Certification infrastructure –Authentication

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Authentication w/ Conventional Crypto Kerberos or Needham Schroeder,4,5 KDC C S

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Authentication w/ PK Crypto Based on public key certificates 1 DS S C 3 2

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Kerberos Third-party authentication service –Distributes session keys for authentication, confidentiality, and integrity TGS 4. Ts+{Reply}Kt 3. TgsReq KDC 1. Req 2. T+{Reply}Kc CS 5. Ts + {ts}Kcs

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Public Key Cryptography (revisited) Key Distribution –Confidentiality not needed for public key –Solves n 2 problem Performance –Slower than conventional cryptography –Implementations use for key distribution, then use conventional crypto for data encryption Trusted third party still needed –To certify public key –To manage revocation –In some cases, third party may be off-line

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Certificate-Based Authentication Certification authorities issue signed certificates –Banks, companies, & organizations like Verisign act as CA’s –Certificates bind a public key to the name of a user –Public key of CA certified by higher-level CA’s –Root CA public keys configured in browsers & other software –Certificates provide key distribution

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Certificate-Based Authentication (2) Authentication steps –Verifier provides nonce, or a timestamp is used instead. –Principal selects session key and sends it to verifier with nonce, encrypted with principal’s private key and verifier’s public key, and possibly with principal’s certificate –Verifier checks signature on nonce, and validates certificate.

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Secure Sockets Layer (and TLS) Encryption support provided between Browser and web server - below HTTP layer Client checks server certificate Works as long as client starts with the correct URL Key distribution supported through cert steps Authentication provided by verify steps C S Attacker Hello Hello + Cert S {PMKey}K s [Cert C + Verify C ] Verify S

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Trust models for certification X.509 Hierarchical –Single root (original plan) –Multi-root (better accepted) –SET has banks as CA’s and common SET root PGP Model –“Friends and Family approach” - S. Kent Other representations for certifications No certificates at all –Out of band key distribution –SSH

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Global Authentication Service Pair-wise trust in hierarchy –Name is derived from path followed –Shortcuts allowed, but changes name –Exposure of path is important for security Compared to Kerberos –Transited field in Kerberos - doesn’t change name Compared with X.509 –X.509 has single path from root –X.509 is for public key systems Compared with PGP –PGP evaluates path at end, but may have name conflicts

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Capability Based Systems - Amoeba “Authentication not an end in itself” Theft of capabilities an issue –Claims about no direct access to network –Replay an issue Modification of capabilities a problem –One way functions provide a good solution Where to store capabilities for convenience –In the user-level naming system/directory –3 columns Where is authentication in Amoeba –To obtain initial capability

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Capability Directories in Amoeba

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Security Architectures DSSA –Delegation is the important issue ▪Workstation can act as user ▪Software can act as workstation - if given key ▪Software can act as developer - if checksum validated –Complete chain needed to assume authority –Roles provide limits on authority - new sub-principal Proxies - Also based on delegation –Limits on authority explicitly embedded in proxy –Works well with access control lists

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Distributed Authorization It must be possible to maintain authorization information separate from the end servers –Less duplication of authorization database –Less need for specific prior arrangement –Simplified management Based on restricted proxies which support –Authorization servers –Group Servers –Capabilities –Delegation

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Proxies A proxy allows a second principal to operate with the rights and privileges of the principal that issued the proxy –Existing authentication credentials –Too much privilege and too easily propagated Restricted Proxies –By placing conditions on the use of proxies, they form the basis of a flexible authorization mechanism

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Restricted Proxies Two Kinds of proxies –Proxy key needed to exercise bearer proxy –Restrictions limit use of a delegate proxy Restrictions limit authorized operations –Individual objects –Additional conditions + Proxy Conditions: Use between 9AM and 5PM Grantee is user X, Netmask is x.x, must be able to read this fine print, can you PROXY CERTIFICATE Grantor

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Authorization and Group Services 1. Authenticated authorization request (operation X) 2. [operation X only]R, {Kproxy} Ksession 3. [operation X only]R, authentication using Kproxy R 2 SC 3 1

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Central Authorization Authorization server uses extended ACLs –Conditions are not evaluated, but instead attached to credentials Groups implemented by auth server –Server grants right to assert group membership Application servers configured to use authorization server –Minimal local ACL –Can use multiple Authorization servers

Copyright © Clifford Neuman - UNIVERSITY OF SOUTHERN CALIFORNIA - INFORMATION SCIENCES INSTITUTE Applied Security Electronic commerce –SSL Applies authentication and encryption –NetCheque applies proxies –SET applies certification –End system security a major issue What we have today –Firewalls –Web passwords, encryption, certificates –Windows 2000 uses Kerberos