Code Mobility in Mobile Agent Systems

1
Code Mobility in Mobile Agent Systems

• Reinier Timmer
• VU, Amsterdam

2
Introduction

• Mobile Agents
• The next generation of information access
• Suited for networking environments
• Transfer computation instead of just data
• Problem program execution on remote hosts

3
Outline

• Introduction to mobile agents
• Code mobility
• Code migration
• Overview of existing mobile agent platforms
• Programming language support
• How (and what kind of) mobility support

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Mobile Agents

• Software object program
• On machine in network
• Represents user
• Can travel network
• Autonomous goal-driven
• Use when
• Accessing protected data
• Bandwidth is low

A
B
A
A
Network
A
C
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Existing methods

• Client-server (CS)
• Remote Evaluation (REV)
• Example active server pages
• Code on Demand (COD)
• Example Java applets
• Agent uses custom code roams a network

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Requirements

• A Mobile Agent system (MAS) needs
• Agent code to be portable
• Agent execution to be resumed remotely
• Main issues
• Choice of programming language
• Protecting host from malicious agents
• Protecting agent from others

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Choice of language

• Native languages (C) probably will not do
• Rather use some interpreted language
• Portability does not imply (easy) migration

data?
data
X
X
state?
B
A
state
Migration
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Code Migration

• How does an agent react upon migration?
• Needs restart weak mobility
• Resumes at next instruction strong mobility
• Problems
• What to transport upon migration
• How to resume execution
• Resource access on remote host

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General layout
Distributed System
Mobile Agent System
Agents
Agents
Applications
True Distributed System
Agent Place
Agent Place
OS
OS
OS
OS
Machine
Machine
Machine
Machine

• Location is explicit in a mobile agent system
• Has influence on agents decisions

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Telescript

• Uses a dedicated language telescript
• Designed for security strong migration
• Only the mobile parts coded in telescript
• Resource migration by concept of ownership

Agents
Telescript Engine
Agentencoding/decoding
agent transport
external applications
resources
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Tacoma

• Mainly uses TCL language (more added)
• A weak mobility model
• Data stored using concept of folders
• Carried with agent in a briefcase
• Left on server in a cabinet
• Agents are just code fragments
• Electronic cash supported
• Runs on Unix, PalmOS, Windows CE/NT,

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Intro to Java-based systems

• Java is a logical language choice
• Code is portable (interpreted)
• Code is mobile (dynamic class loading)
• Type-safe and well-known language
• Object serialization makes transport easy
• But runtime state is not transported
• A lot of attacks are known
• Security needs to be well-configured

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IBM Aglets

• Uses standard Java model
• Transport uses serialization
• Weak mobility
• Aglet server clearly separated
• Context is interface to host
• Proxy is interface to agent

A
Proxy
Context
Aglet Server
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Ajanta

• Uses standard (weak mobile) Java model
• Emphasis on
• Fault tolerance (local guardian object)
• Agent integrity protection (protected containers)
• Credentials for resource access
• Some special protection measures (by Java)
• Separating class loaders
• Thread grouping

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ARA

• Multiple languages (TCL, C/C, Java)
• But still it provides strong mobility

TCL
C
C
Java
TCL interpreter
C/C interpreter
Java VM
ARA core
Host OS
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ARA

• Uses interpreters for language-specific tasks
• A modified JVM TCL interpreter
• Special compiler interpreter for C/C

TCL
C
C
Java
TCL interpreter
C/C interpreter
Java VM
ARA core
Host OS
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ARA

• Generic routines reside in ARA core system
• Global local allowances limit resource access

TCL
C
C
Java
Agents

• state capturing
• memory protection

TCL interpreter
C/C interpreter
Java VM
Two-way interface

• agent transport
• resource control

ARA core
Host OS
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DAgents (Agent TCL)

• Multiple languages (Java, TCL, Scheme, )
• Mobility depends on what interpreter supplies

Agents
Java
TCL

Server/Engine
TCP
Email

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DAgents (Agent TCL)

• General language plugin structure

Interpreter
Agents
Statecapture
languagesecurity
Java
TCL

Server/Engine
Server API
TCP
Email

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DAgents (Agent TCL)

• Heavy focus on security protection
• Security managers supported by language
• Resource managers for resource access

Interpreter
Agents
Statecapture
languagesecurity
Java
TCL

Server/Engine
Server API
TCP
Email

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Conclusions

• Choice of language is essential for MA system
• Influences level of mobility
• Some (basic) security measures
• Language support is but one aspect
• Ensuring agent integrity
• Protection of host
• New research trends more towards security
• Essential for real (E-business) applications

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QA
???