Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Language-Based Information- Flow Security Andrei Sabelfeld Andrew C. Myers Presented by Shiyi Wei

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Literature review  Information flow security Static program analysis to enforce information-flow Confidentiality  Year: 2003  Jif (Java information flow) project  Active since 1997  More than 34 publications System, language, security – SOSP, POPL, CCS, Oakland  Other work based on Jif 2 About the paper

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Introduction  Background  Covert channels  Mandatory access control  Basics of language-based information flow  Research trends  Open challenges 3 Overview

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Protect data confidentiality  End-to-end security  Enforcement of confidentiality policies Information cannot flow to where policy is violated  Challenges Concurrency Covert channels  Applications Military, medical, financial information systems Web-based services: mail, shopping, social network 4 Introduction

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Standard security mechanisms  Discretionary access control Access files/objects based on privilege – Prevent processes not authorized by file owner from reading Place restrictions on the release of information, but not its propagation – Does not control how the data is used after reading from file To soundly enforce confidentiality – Grant access privilege only to processes that will not leak confidential data » A much stronger information-flow policy! » Access control cannot identify these processes 5 Introduction

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Standard security mechanisms  Encryption Secure an information channel – Only the communicating endpoints have access However, no assurance that once the data is decrypted  Antivirus software Offers limited protection against new attacks  Firewall Protects confidentiality by preventing communication Checking confidentiality violation lies outside its scope 6 Introduction

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Language-based approach  security-typed language Use of type systems for information flow – Augmented with annotations Specify policies on the use of the typed data Compile-time type checking – Add little or no run-time overhead E.g. Jif[1], SLam calculus[2], … 7 Introduction References [1] A.C.Myers and B. Liskov, “A decentralized model for information flow control,” in Proc. ACM Symp. on Operating System Principles, Oct. 1997, pp [2] N. Heintze and J. G. Riecke, “The Slam calculus: programming with secrecy and integrity,” in Proc. ACM Symp. on Principles of Programming Languages, Jan. 1998, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Integrity: a dual to confidentiality  “Confidentiality requires that information be prevented from flowing to inappropriate destinations”  “Integrity requires that information be prevented from flowing from inappropriate sources” 8 Introduction

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Implicit flows  Signal information through the control structure of a grogram  Termination channels  The termination/nontermination of a computation  Timing channels  Signal information through the time at which an action occurs rather than through the data E.g. total execution time of a program 9 Background: Covert Channels while secret=1 do skip

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Probabilistic channels  Signal information by changing the probability distribution of observable data  Resource exhaustion channels  Signal information by the possible exhaustion of a finite, shared resource  Power channels  Signal information in the power consumed by the computer 10 Background: Covert Channels

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Mandatory access control  Label each data with a security level Run-time enforcement mechanism  Problem: implicit flow Process sensitivity label  Label creep Monotonically increase label Too restrictive 11 Background: Mandatory Access control h := h mod 2; l := 0; if h = 1 then l :=1 else skip h := h mod 2; l := 0; if h = 1 l := 1 skip

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Noninterference policy  “a variation of confidential(high) input does not cause a variation of public(low) output”  The attacker cannot observe any difference between two executions that differ only in their confidential input  Security-type system  A collection of typing rules  Let’s build one! 12 Basics of Language-Based Information Flow

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 13 Basics of Language-Based Information Flow Language syntax: C ::= skip | var := exp | C1;C2 | if exp then C1 else C2 | while exp do C

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 14 Basics of Language-Based Information Flow Language syntax: C ::= skip | var := exp | C1;C2 | if exp then C1 else C2 | while exp do C (1) := (2) := (3) := (4) :=

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 15 Basics of Language-Based Information Flow C ::= skip | var := exp | C1;C2 | if exp then C1 else C2 | while exp do C (1)if then else (2)if then else (3)if then else (4)if then else (5)if then else (6)if then else (7)if then else (8)if then else

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 16 Basics of Language-Based Information Flow Language syntax: C ::= skip | var := exp | C1;C2 | if exp then C1 else C2 | while exp do C

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 17 Research Trends static certification noninterference sound security analysis expressiveness concurrency covert channels security policies

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 18 Language Expressiveness static certification noninterference sound security analysis expressiveness concurrency covert channels security policies procedures functions exceptions objects

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Procedures  Polymorphism[3] The type of commands or expressions may be generic  Functions  Slam calculus[4] A functional language 19 Language Expressiveness References [3] D. Volpano and G. Simth, “A type-based approach to program security,” in Proc. TAPSOFT’ 97. Apr. 1997, vol of LNCS, pp [4] N. Heintze and J. G. Riecke, “The Slam calculus: programming with secrecy and integrity,” in Proc. ACM Symp. on Principles of Programming Languages, Jan. 1998, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Exceptions  Nonlocal transfer of control; implicit flow  Path labels[5] Fine-grained tracking of implicit flows caused by exceptions  Objects  Java-like imperative object-oriented language[6]  JFlow[5] 20 Language Expressiveness References [5] A. C. Myers, “JFlow: Practical mostly-static information flow control,” in Proc. ACM Symp. on Principles of Programming Languages, Jan , pp [6] A. Banerjee and D. A. Naumann, “Secure information flow and pointer confinement in a Java-like language,” in Proc. IEEE Computer security Foundations Workshop, June 2002, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 21 Concurrency static certification noninterference sound security analysis expressiveness concurrency covert channels security policies non- determinism threads distribution

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Nondeterminism  Possibilistic security condition[7] High inputs may not affect set of possible low inputs  Dependence analysis between variables[8] 22 Concurrency References [7] J. McLean, “A general theory of composition for a class of “possibilistic” security properties,” IEEE Transactions on Software Engineering, vol. 22, no. 1, pp , Jan [8] J. –P. Banatre, C. Bryce, and D. Le Metayer, “An approach to information security in distributed systems,” in Proc. European Symp. on Research in Computer Security. 1994, vol. 875 of LNCS, pp , Springer-Verlag.

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Thread concurrency  High part has to be protected at all times  Noninterference for a multithreaded language[9] No while loop may have a high guard No high conditional may contain a while loop in branch  Encode of a timing leak into a direct leak 23 Concurrency (thread1) h := 0; l := h; (thread2) h := h’ (if h = 1 then C long else skip); l :=1 || l := 0 References [9] G. Simth and D. Volpano, “Secure information flow in a multi-threaded imperative language,” in Proc. ACM Symp. on POPL, Jan. 1998, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Distribution  The ability to exchange messages These communications may be observed by attackers  Mutual distrust  Components can fail Attempt to compromise the behavior of others  Secure program partitioning[10] Sequential, security-typed program -> fine-grained communicating subgrams 24 Concurrency References [10] S. Zdancewic, L. Zheng, N. Nystrom, and A.C. Myers, “Untrusted hosts and confidentiality: Secure program partitioning,” in Proc. ACM Symp. on Operating System Principles, Oct. 2001, pp. 1-14

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 25 Covert Channels static certification noninterference sound security analysis expressiveness concurrency covert channels security policies termination timing probability

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Termination channels  Termination-sensitive noninterference[11] Disallows high loops and requires high conditionals have no loops in the branches  Binding-time analysis[12] Divides program terms into – Static: known at partial-evaluation time – Dynamic: to be supplied later No static term depends on a dynamic variable 26 Covert Channels while h = 1 do skip References [11] D. Vlpano and G. Smith, “Eliminating covert flows with minimum typings,” Proc. IEEE Computer Security Foundations Workshop, pp , June 1997 [12] M. Abadi, A. Banerjee, N. Heintze, and J. Riecke, “A core calculus of dependency,” in Proc. ACM Symp. on Principles of Programming Languages, Jan. 1999, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Timing channels  Timing-sensitive noninterference[13] High conditionals have no loops in the branches and wrapping each high conditional in a protect statement whose execution is atomic  Program transformation[14] Cross-copy of the slices of the branches of a high if to equalize the execution time of the branches 27 Covert Channels if h = 1 then C long else skip References [13] D. Volpano and G. Smith, “Probabilistic noninterference in a concurrent language,” J. Computer Security, vol. 7, no. 2-3, pp , Nov [14] J. Agat, “Transforming out timing leaks,” in Proc. ACM Symp. on Principles of Programming Languages, Jan. 2000, pp

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Probabilistic channels  Probabilistic noninterference Two behaviors are indistinguishable by the attacker iff the distribution of low output is the same  Example [] p : probabilistic choice operator – Selects the left-hand side command with the probability p – Selects the right-hand side with the probability 1-p Varying PIN does not change set of possible outcomes – Secure for possibilistic condition 28 Covert Channels l := PIN [] 9/10 l := rand(9999)

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science 29 Security Policies static certification noninterference sound security analysis expressiveness concurrency covert channels security policies declassification admissibility relative security quantitative security

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Noninterference rejects downgrading  Decentralized model[1]  Selective declassification  Admissibility[15]  Explicitly states what dependencies between data are allowed in the program  Quantitative security[16]  Allow for a limited bandwidth of information leaks 30 Security Policies References [15] M. Dam and P. Giambiagi, “Confidentiality for mobile code: The case of a simple payment protocol,” in Proc. IEEE Computer Security Foundations Workshop, July 2000 [16] D. Clark, S. Hunt, and P. Malacaria, “Quantitative analysis of the leakage of confidential data,” in QAPL 2011.

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  System-Wide Security  Computer systems are only as secure as their weakest point  Integration of language-based information flow and system-wide information-flow control  Certifying Compilation  Secure information flow of low-level languages Useful information about program structure is lost 31 Open Challenges

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Abstraction-violating attacks  The model of the attacker is an abstraction Removes possibly important details about real attacker  E.g. cache attack When h = 1, execution time is likely to be shorter  Dynamic Policies  Information-flow policies are not known statically  E.g. Jif compiler Type label 32 Open Challenges (if h =1 then h’ := h 1 else h’ := h 2 ); h’ := h 1

Fall, Privacy&Security - Virginia Tech – Computer Science Click to edit Master title style Fall, Privacy&Security - Virginia Tech – Computer Science  Practical issues  Improve the precision of type systems Do not reject too many secure programs  Experience is needed  Variations of static analysis for security  Control- and data-flow analysis More accurate than many type systems  E.g. 33 Open Challenges (if h = 1 then l := 1 else l:= 0); l := 0