PSU CSE 543 - Systems and Midterm Review (17 pages)

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Systems and Midterm Review



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Systems and Midterm Review

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Pages:
17
School:
Penn State University
Course:
Cse 543 - Computer Security
Computer Security Documents
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Lecture 18 Systems and Midterm Review CSE543 Fall 2007 Computer and Network Security Professor Jaeger October 30 2007 CSE543 Computer and Network Security Fall 2007 Professor Jaeger Understanding Data Lifetime What happens to data in a system Where do secrets go Handled by Hardware systems middleware applications drivers etc How to find leaks and solve them CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 2 Data Lifetime How long memory values reside on a system Allocate a buffer Assign a secret Free the buffer Q What happens to the memory during and after this cycle What happens to freed memory Data may be written elsewhere used for other purposes Q What s the threat model here Key and other secrets protection is paramount CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 3 Can t Be That Hard Typical solutions Zero the memory on free Pin memory so not written to swap Encrypted file systems Problems Compilers may not comply Zeroing code on free buffers is optimized out Crashes Incorrect features don t really pin memory Hibernation and Migration Write state of system Complex interactions of logging random number generation crash dumps error reporting etc CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 4 Understanding Approach Whole System Simulation TaintBochs extension of IA 32 simulator Key Ideas Shadow Memory Backup of all existing memory registers and main memory Propagation Policy If any byte of any input value is tainted then all bytes of the output are tainted Exceptional Cases Tainted lookup tables Add more tainting Constant functions Remove unnecessary tainting Tainted Inputs Device inputs all keyboard or patterns network Application state what data is tainted to the system CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 5 Analysis Log everything All changes in system state at any point in simulation System states Can generate the state of the system at any time Identify Data Map memory and registers to source variables Program and line number where variable was defined Patch Linux kernel to store this or core dump reading Identify Code Find line number of modifying code Can also enact gdb to use most features from a state CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 6 Findings Mozilla browser What happens to a user input password Ends up in Linux tty buffers Linux Random number generator Xserver input queue Linux UNIX domain socket buffers Mozilla strings Everyone in path allocates memory Sometimes for multiple purposes Free d but not zero d Memory is still around until reused May also be copied to other variables CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 7 Fixes Some are easy Heap memory Ensure memory is zero d Stack memory Zero the stack frame Some are harder Stores built from tainted data Random number and others in memory Stores written to other places Swap encrypt it Logs etc Encrypt them CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 8 What Does This Say About Security Systems Security Involves interactions at multiple levels OS Devices Application Services X Window System Users Function Is Defined By Code What does that instruction do What is its security impact Can programmers express this Or can we figure it out Can it be conveyed into a form that users can work within Not around CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 9 Midterm 11 1 In class Closed book and closed notes Contents 1 3 crypto and 2 3 systems security Crypto Scope is same as mini exam Questions will be closely related but no same or subsumed by mini exam Systems Principles Systems Approaches Some times compare them CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 10 Security Terminology Adversary Risks Vulnerability Threats Compromise Trust Trust Model Threat Model CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 11 Cryptography Encryption Decryption Symmetric Key Systems DES One time pads Public Key Systems RSA Diffie Hellman Hash Functions Uses Properties Combinations of these into protocols Threats to crypto systems use CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 12 Authentication Key distribution Needham Schroeder Secret and public key Kerberos Protocol Basics Extensions to NH Kerberos Flaws Public Key Infrastructure Use Limitations CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 13 Trusted Computing Hardware for Security Protected Storage Hash Extends Sealed Storage IMA Model Paper What can really be done Issues Trust and DRM CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 14 Systems Security Access Control Fundamentals Protection State Protection System Reference Monitor Access Matrix Policies Secrecy Bell LaPadula MLS Integrity Biba LOMAC Clark Wilson Goals Properties How represented how achieved ACLs and Capabilities Functions and issues CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 15 Systems Architectures Protection systems UNIX Windows Features used for protection and or security Secure Systems Sandbox Systems Secure Capability Systems Multics SELinux Domain transitions Programming language vulnerabilities Security typed languages Related to HW SELinux and Security Typed Languages CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 16 Good Luck CSE543 Computer and Network Security Fall 2007 Professor Jaeger Page 17


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