Making Ambients More Robust

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Making Ambients More Robust

• Xudong Guan
• Distributed Computing Technology Center
• Shanghai Jiao Tong University
• WCC-ICS2000, Beijing, Aug 22th, 2000

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Calculi for wide area and mobile computation

• The pushing forces behind
• Internet, laptop, WAP, H21
• Network computing, mobile agent
• A few examples (related work)
• ?-dist _at_ Tokyo U.
• Variations of ?-calculus
• Distributed Join calculus
• Seal calculus

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Ambient calculi

• Mobile Ambient (MA)
• Safe Ambient (SA)
• Robust Ambient (ROAM) - this work

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The Mobile Ambient calculus

• An exampleapout a.in b.?M? bopen p.(x).P
  
• Ambient
• a..., p..., b...
• Capabilities
• Movement (in?out), action (open)
• Local communication
• output ?M?, input (x).P

root
a
b
p
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The grave interference in MA

• h nin h mout n.P

• first in then out? hnmout n.P ? hn
  mP

• first out then in ? h nin h mP ?
  hn mP

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Safe Ambient
The key of the reduction order

• hin h nout n.in h mout n.P? hin h
  nin h mP? hn mPcoactions(in,
  out, open) guarantee the reduction order and
  eliminate the grave interference in MA

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Malicious tampering of coactions in SA

• nin m.open n.P min m.open n.Q hin m
  desired redex
• nin m.open n.P min m.open n.Q hin m
  malicious
  tampering

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SolutionExplicit coaction parameter

• nin m.open n.P min n.open n.Q hin
  mThis coaction could only be consumed by n
• hence the Robust Ambient calculus

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Type system for ROAM

• Mobility - mobile, immobile
• Threads - 0, 1, 1, n
• Why 1 ? Example nopen m.P
  mQAssume Q is single threaded,n seen to be
  single threaded as well, but this depends on P ...

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The expressiveness of ROAM

• Firewall crossing
• Asynchronous ?-calculus
• Message exchange in named ambients
• Can even encode ?-calculus with pure ROAM
  calculus (without message exchange) - our next
  paper.
• Substitution and message exchange in named
  ambients

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Thank you!

• For more information, please visitXudong Guans
  Mobile Ambient page athttp//go.163.com/mobile
  ambient/(online papers, researchers, other
  resources related to Ambient calculi)