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Towards Remote Policy Enforcement for Runtime Protection of Mobile Code Using Trusted Computing

Towards Remote Policy Enforcement for Runtime Protection of Mobile Code Using Trusted Computing. Xinwen Zhang Francesco Parisi-Presicce Ravi Sandhu www.list.gmu.edu George Mason University IWSEC 2006. Mobile Codes and Agents.

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Towards Remote Policy Enforcement for Runtime Protection of Mobile Code Using Trusted Computing

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  1. Towards Remote Policy Enforcement for Runtime Protection of Mobile CodeUsing Trusted Computing Xinwen Zhang Francesco Parisi-Presicce Ravi Sandhu www.list.gmu.edu George Mason University IWSEC 2006

  2. Mobile Codes and Agents • programs that migrate and execute at remote hosts, so that the execution environments are different for different instances • Downloaded executables, Java applet, ActiveX components, Servlet/EJB components, etc. • Two types of security problems: • Type I: Protect a local host (where a mobile code is executing) resources to prevent malicious access from mobile code • Protect host’s files/dirs, sockets, memory space, etc. • Type II: Protect mobile applications from malicious hosts • Sensitive information/functions with mobile codes

  3. Security in Type I • Runtime policy enforcement on local host • Common Language Runtime (CLR) and Java Runtime Environment (JRE) • Policies are based on attributes of codes and users • JDK1.0/1.1: code-identity based model • Simple sandbox model • Sandboxing based on code sources, URL (where the code is downloaded, signature, etc. • JDK1.2: user & code attribute based model • User attributes—Java Authentication and Authorization services • Identity-based, role-based, group-based, general certificate-based, etc. • Augmented with local operating system’s access control policies

  4. Java Security • Sample policies: granting permissions based on: • Code URL • Code signature • Solaris authenticated principal name • Kerberos authenticated Principal name

  5. Mechanism • Initial steps for security check in JVM: • Type safety checks for language by Verifier • Classloader loads bytecode and check signatures and code source • Construct security policy in terms of protection domain • Class is “defined” and public available to run in JRE • Every time the class tries to access a system resources, its permissions are checked by security manager (or access controller). • Stack inspection mechanism is used in access controller to enforce security policy • Rights of a piece of code is a function of the state of the execution stack. • Same mechanism is applied in .Net (stack walk)

  6. Motivations for Mobile Policy for Type II Security • Enforce code originator’s policies when the code is remotely executing: • a shopping application carrying user’s sensitive information while running in a remote site. The code originator may require that the code can only run in a specific protected domain, and the user who runs this code must have a specific role in an organization, or some other credentials. • Enforce enterprise-wide security policies for codes deployed in many platforms within an enterprise • Extensible and scalable policy definition • Policies can be reused, revoked and updated • Flexible policy management • Centralized or decentralize • Fine-grained policy specification based on users, target services, and system conditions

  7. Challenges and Solutions • Challenges: • Need trusted runtime environment to Enforce Mobile Policies • trusted by policy stakeholder (e.g., mobile code originator/owner) • Need policy enforcement mechanism with minimum changes in existing security architecture • Solutions: • Trusted computing enabled runtime environment • Leveraging stack-based security check by dynamically loading external policy file • Viable with the separation of policy definition and enforcement in JVM

  8. Trusted Runtime Environment (TRE) • Trust Model: Integrity measurement and secure boot • TPM -> Secure Kernel -> JVM -> Mobile code & policy • Primitive functions of TRE: • Integrity measurement and attestation response of mobile code & policy from code originator • Integrity measurement and attestation of security components: • JAAS for trusted user authentication • PDP for trusted access control enforcement

  9. Mobile Policy Specification • Logically, each code is associated with one policy file • XACML policy specification: • Extensible policy specification language • Support policy composing and derivation <Policy PolicyId="(policy-name)" PolicyCombinationAlg="rule-combining-algorithm:permit-overrides"> <Target> <Subjects>(predicates over subject attributes)</Subjects> <Resources>(predicates over object attributes)</Resources> <Actions>(predicates over access rights such as read and write)</Actions> </Target> <Rule effect="permit"/> (Specification that this policy is positive) <Obligations>(Specification of attribute-update actions)</Obligations> </Policy>

  10. Policy Model • Subject attributes: • Identity, role, Group, Clearance level • General credentials • Objects • Sensitive information presented and accessed by mobile code • Components, classes, methods, variables • permissions • Initialization components and classes • invoke methods • Access (read/write) variables

  11. Policy Enforcement • Sun’s XACML library • PDP module • Evaluated XACML policy file with XMLPolicy class • Loading XACML policy file need local privilege in JVM • Access control algorithm • Stack-inspection mechanism <Policy PolicyId="makeorder-policy" <Subjects>… <AttributeValue DataType="string">OU=Org1</AttributeValue> <SubjectAttributeDesignator AttributeId="subject-id“ DataType="x500Name"/>… <AttributeValue DataType="string">PurchaseManager</AttributeValue> <SubjectAttributeDesignator AttributeId="subject-rolename" DataType="string"/>... </Subjects> <Resources>… <AttributeValue DataType="string">creditPermission</AttributeValue> <ResourceAttributeDesignator AttributeId="permission-name" DataType="string"/>… </Resources> <Actions> <Action>GET</Action><!-- "GET" represents the read privilege. --> </Actions> <Rule effect="permit"/> </Policy>

  12. Revocation • Revocation because of • Policy revocation • Trust revocation of a component in JVM • E.g., JAAS, access controller, XACML PDP • Trust revocation of a TRE • Trust revocation of a platform • Two approaches: • Push: code owner sends updated policy to client side • Pull: client side checks policy update whenever loads a code • Both may have delayed revocation • Instant revocation needs centralized policy server

  13. Related Work • Protection of local host against malicious code • Safe Interpreters • Saft-Tcl (J.K.Ousterhout et al ‘97) • Telescript/Odyssey (J.Tardo et al ‘96) • Runtime environment security • Code-signing • Sandbox (JDK 1.0) • Extended sandbox(JDK1.1, 1.2) • .Net CLR security • Proof-carry (P.Lee et al ‘97) • Protection of mobile code against malicious host • Secure coprocessor (B.Yee, 1994) • Encrypted function. (J. Algesheimer et al ’01) • Trusted JVM (Halder et al ’04)

  14. Conclusions & Future Work • A mobile policy framework to protect mobile code from execution host • A policy model • A trusted runtime environment • Policy enforcement mechanisms with XACML and Sun PDP module • Future Work • Runtime policy analysis engine • Dynamically derive policy info from multiple policy files • For decentralized policy definition and management • A comprehensive policy model

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