Computer

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Secure and Reliable Embedded Systems Laboratory

• Kishore Dhaveji

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Robust Object Calculus

• A Process Calculus used both as an Executable
  Model as well as for System Verification.
• Models concurrent objects
• Supports complex message passing
• Encapsulation Security

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Meta-Object Model

• Provides common substrate for securely
  interoperable heterogeneous distributed objects.
• Permits the development and interoperation of a
  variety of Object Oriented Systems.
• Implements a meta-level architecture for a method
  based access control of meta-objects.
• Based on ROC.

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Object Oriented Systems

• Composed of classes, instances (objects),
  attributes (instance variables) and methods.
• Supports encapsulation, modularity and re-use
  through message passing, inheritance and
  aggregation.
• Objects encapsulate state and service.
• Classes are templates for instances.

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Meta-Object Models

• Supports classes, subclasses and inheritance.
• Supports method invocation, message passing and
  aggregation.

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How MOM differs from OOS

• Classes and Objects are modeled by meta-objects.
• Meta-objects can spawn other meta-objects.
• Meta-objects capable of spawning class
  meta-objects are called meta-classes.
• Method invocation is sent in the form of messages
  between two objects.

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MOM Objects

• Are a collection of tightly encapsulated agents.
• Identifiers in MOM objects define how the objects
  can be addressed.

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Composition of MOM Objects

• Message Handler
• Object Information Repository
• Object Registries (OR)
• Object Access Control List (OACL)
• Metadata repository (MD)
• Object Contents
• Methods
• Sub Objects

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MOM Object Components
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Object Information Repository

• Object registries contain useful information
  about each component that resides in MOM.
• Local identifier (lid), component type, and other
  information stored in registry record.
• Metadata repositories contain information
  intended to describe class and interface
  behaviour.

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Object Information Repository

• Object access control lists (OACL) define the
  local authorization state of MOM object.
• Contents of OACL can be changed issuing
  authorization commands.

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Object Information Repository

• Structure of record in OACL
• Ex.1 states that
  interface1 has lock associated with token a. i.e.
  interface1 is accessible to all messages having
  a tickets.
• Ex.2 states that b is a ticket
  held by Arbiter2.

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Messages

• Messages are ROC agents that expose values that
  encapsulate message content within appropriate
  domain.
• MOM messages is a persistent entity in the
  system.
• All messages exist until consumed by a message
  handler.

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Messages

• Messages are of the following types
• Requests
• Replies
• Acknowledgements
• Authorization Commands

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Message Handlers

• Processes and delegates incoming messages.
• At times interacts with method interfaces (for
  method invocation requests) and method arbiters
  (for method replies).

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Method Components

• Method Interfaces
• Used to control access to individual methods.
• Receives the invocation request created by a MOM
  message handler.
• Unique method interface for each method in an
  object.
• Communicates with method arbiters.

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Method Components

• Method Arbiters
• Designed to manage communication of individual
  method bodies.
• Responsible for creating method bodies and
  marshaling their input and output.
• Method bodies
• ROC expressions constrained to obey necessary
  interface and encapsulation principles.
• Perform the work of methods.

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MOM Methods

• Perform operations on primitive data types and/or
  issues other method invocation requests.
• There are two types of methods
• Immutable methods
• Mutable methods

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Immutable Methods

• Do not contain state information.
• They are functional methods that return value.
• Serve as interface to instance variables.
• Spawns a new Method Body.

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Mutable Methods

• Have state associated with them.
• They model instance variables.
• Can be accessed many times.
• They spawn a single Method Arbiter and Method
  Body in the whole life time.

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Security in MOM

• Tickets, Message filters and OACLs implement
  access control in MOM systems.
• Tickets are unforgeable tokens visible only to
  trusted processes (MF OACL).
• Message filters accept messages by comparing
  embedded tickets with the local authorization
  states of objects.
• Local authorization states of an object are
  recorded in its OACL.

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Security in MOM

• Based on 3 models
• Ticket Based Security
• Authorization Model
• Ticket Based Access Control

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Programming Access Control

• Discretionary Access Control
• Mandatory Access Control
• Role Based Access Control
• Task Based Access Control