Issues Relevant To Distributed Security xuhong Zhang

 Security in Distributed Systems  Popular Security Mechanism in Distributed Systems  Protection Methods Against Security Threats  Complex Security Policies  Concept of Proxy  Covert channels  Traffic analysis prevention  Auditing  Current research  Future work OUTLINE

 Different from operating system security:  No central trusted authority that mediates interaction between users and processes.  Distributed system runs on top of a large number of loosely coupled autonomous hosts, that maybe running different OS’s with possibly different security policies.  So, issue of security becomes even more complex in Distributed Systems.  Two Key Terms  Objects, example:- a file  Subjects, example:- a user Security in Distributed Systems[1]

 Authentication  Allows only authentic subjects to have access to the system.  Authorization  Allows an object access only to authorized subjects.  Auditing  Process of maintaining an audit log which records all activity. This helps in tracing security attacks. Protection Methods Against Security Threats [2]

Complex Security policies  The Access Control List (ACL) and Capability List (CL) security models are stateless. Properties remain fixed unless explicitly changed by the server.  Complex Access Control Policies are state dependent. Authorization of access depends on subjects past history and interaction with other objects. [1998 Chow and Johnson]

 Complex access control policies have state dependent security requirements.  Example:- A security policy which decides its course by reading the subject’s past access history:  A subject S is not allowed to access object O1 if it has read object O2.  “If” is the keyword here which makes the security policies in distributed systems state dependent. …..Complex Security policies[2]

 Information flow model:  lattice structure in which information can flow in the direction the properties used to construct the lattice permit.  But, In Distributed Systems,  There are some applications which need information flow which violates some properties of lattice.  These are called information flow exceptions. Multilevel Information Flow Exceptions[2]

 There are 3 types of information flow exceptions:  Transitivity: A->B and B->C implies A->C  Transitivity exception : A->B and B->C but A-/->C  Aggregation: A->C and B->C implies A U B ->C  Aggregation exception: A->C and B->C, but A U B -/->C  Separation: A U B ->C implies A->C and B->C  Separation exception: A U B ->C,but A -/-> C and B -/-> C ….. Multilevel Information Flow Exceptions[2]

 Main operations between entities in access control are:  Read(confidentiality)&Write(integrity).  So, A → B means A writes information to object B. Redefining flow exceptions in terms of Access Control[2]

……Redefining flow exceptions in terms of Access Control[2]

Computer Automated Bank Loan Application  Only clerk(S 1 ) can prepare loan application (write permissions for object O).  One of two bank officers, the manager (S 2 ) or accountant (S 3 ) (but not both) must approve the application (append permissions).  Approved loan is the appended with electronic check signed by both bank manager (S 2 ) and cashier (S 4 ). Example of a Complex Access Control Policy

Graphical Representation

 Definition:  A “Proxy” is a certificate which verifies that a subject has truly given a subset of its rights to another subject for performing some tasks on its behalf.  Usage example:  A client process makes a request to a print server to print a file.  The client can make the print server its proxy. Proxy and its use[2][3]

 Amount of file transfer in the network is reduced.  Client does not have to wait for print server even if it does not have sufficient buffer space for the file at the time of the request.  So, the delegation of responsibilities to proxies improves the efficiency of processing. Advantages of Proxy[2][3]

 Definition:-  A communication path that conveys information illegitimately by seemingly legitimate use of computer resources.  Maybe intentional or unintentional  Traditionally, categories of covert channels:  Storage channels  Timing channels  Network covert channels Covert Channels[2][4]

 The key is to regulate information flow in the network such that the spatial and temporal imparity of the network traffic pattern is reduced.  Common approaches:-  Encryption  Padding  Routing  Scheduling Traffic Analysis Prevention[2]

 Passive protection – acts as a last resort when other mechanisms such as authentication and authorization are not sufficient to protect the security of the system  Can be performed online in the firewalls for early detection of threats or offline when an attack or problem has already occured  Maintain log files that record all activity in the system and the network Auditing

 Security policy conformance is a crucial issue in large- scale critical cyber-infrastructure  Previous methods do not adequately addressed the issue of scaling to networks of thousands of nodes or of resilience to attacks  This new approach addresses the scaling problem by decomposing policies and distributing the validation process Current Research Distributed Security Policy Conformance

 Each of the complex rules that define the compliant and non-compliant states of the system is decomposed into local components and an aggregate component  Securely delegate the validation of local components to secure agents installed on hosts.  These agents are able to reliably monitor the state of the system using virtual machine introspection.  Using this information, we partition the validation of aggregate components across several distributed servers. Current research

 One approach in auditing : Artificially Intelligent systems that enforce security policies and detect/prevent attacks based on past occurrences and heuristics Future Work

 [1]. Feng, Fujun; Lin, Chuang; Peng, Dongsheng; Li, Junshan. “A Trust and Context Based Access Control Model for Distributed Systems” High Performance Computing and Communications, HPCC '08. 10th IEEE International Conference on Sept Page(s):629 – 634 High Performance Computing and Communications, HPCC '08. 10th IEEE International Conference on  [2]. Distributed Operating Systems & Algorithms, Randy Chow and Theodore Johnson, Addison Wesley,  [3]. Dave, A.; Sefika, M.; Campbell, R.H.; “ Proxies, application interfaces, and distributed system” Object Orientation in Operating Systems, 1992., Proceedings of the Second International Workshop on Sept Page(s): Object Orientation in Operating Systems, 1992., Proceedings of the Second International Workshop on  [4]. 1 Nov.,2008  [5]. Montanari, Mirko, Chan Ellick, Larson Kevin, Yoo Wucherl, and Campbell Roy H. “Distributed Security Policy Conformance”, 2011Distributed Security Policy Conformance REFERENCES