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A Parametric Tool for Applied Process Calculi: PsiCalculi Workbench
Johannes Borgström Ramūnas Gutkovas Iona Rodhe Björn Victor
Uppsala University, Sweden
supported by ProFuN and

Motivation
• Application Specific Reasoning • Parametric • Dynamic Connectivity • Mobility • PsiCalculi Workbench

PsiCalculi Workbench (Pwb) Features
Parametric On
Unicast
Wireless Broadcast
Communication Primitives
Data Structures
Logics
Logical Assertions
e.g., Names, Bits, Vectors, ADTs, Trees, ...
e.g., EUF, FOL, Equational Theory, ...
e.g., Knows a secret, Connectivity, Constraints...

Pwb Functionality
P ⇠ Q
Symbolic Execution
Symbolic Behavioral Equivalence Checking
. P↵�!C
P 0
ConstraintsAssertion

Pwb implements PsiCalculi
• PsiCalculi is a parametric process calculi framework
• Designed for applications (WSNs, Cache Coherence, Security Protocols, etc.)
• The soundness of the metatheory has been machinechecked with Isabelle (algebraic laws, bisimulation theory, compositional semantics, etc.) inherited by all calculi [to appear in JAR]
• Symbolic Semantics and Bisimulation Checking Algorithm [JLAP’12]
[LMCS‘11]Just
Add Data
and Logic

PsiCalculi Expressiveness• Captures:
• Cryptography as in the applied picalculus by (Abadi, Fournet 2001) • Fusion as in the explicit fusion calculus by (Wischik, Gardner 2005) • Concurrent Constraints as in the concurrent constraint calculus by
(Buscemi, Montanari 2007)
• Polyadic Synchronization (Carbone, Maffeis 2002) • Extensions:
• Higher Order Processes [to appear in MSCS] • Wireless Broadcast Communication [SEFM’11] • Generalized pattern matching and sorts [to appear in TGC’13] • Parametrized type system for Psicalculi by (Hüttel 2011)

VINN Excellence Center WISENET 2009
PsiCalculi Workbench via an Example
Data Collection in Wireless Sensor Network
graphic from WISENET

Purpose of the Example
• Demonstrate the features of Pwb • Demonstrate the functionality of Pwb • Applicability of Pwb to WSNs

Data Collection in Wireless Sensor Networks
• Network consists of a set of nodes and one distinguished node sink
• Protocol has two phases: 1. Establishment of a routing tree
(rooted at sink): nodes wirelessly broadcast a special initialization message.
2.Data collection: nodes send and forward data via established route using (reliable) unicast messages
✰
✰

Specification in Pwb
Sink(nodeId, sinkChan)

Specification in Pwb
Sink(nodeId, sinkChan)

Specification in Pwb
Sink(nodeId, sinkChan)

Specification in Pwb
Sink(nodeId, sinkChan)

1 2
Sink
Node Node
Node Connectivity for Broadcasting
0
(0,1), (0,2), (1,2)
graph represented as edge list
Pwb Features
Sink(nodeId, sinkChan)

1 2
Sink
Node Node
Node Connectivity for Broadcasting
0
(0,1), (0,2), (1,2)
graph represented as edge list
Pwb Features
Sink(nodeId, sinkChan)

1 2
Sink
Node Node
Node Connectivity for Broadcasting
0
(0,1), (0,2), (1,2)
graph represented as edge list
Pwb Features
Sink(nodeId, sinkChan)

Establishment of a Routing Tree (1)
(!("data(sinkChan)"(gnb). ProcData))  (((new chan1)( '"init(1)"!. '"data(sinkChan)". !("data(chan1)"(gnb). '"data(sinkChan)")))  ((new chan2)( '"init(2)"!. '"data(sinkChan)". !("data(chan2)"(gnb). '"data(sinkChan)"))))
0
1 2
Sink
Node Node
(new sinkChan) Sink  (new chan1) Node  (new chan2) Node
"init(0)"!(new sinkChan)sinkChan
sinkChan sinkChan
broadcastscan unicast
▹ connectivity as current assertion
true

Establishment of a Routing Tree (2)
0
1 2
Sink
Node Node
"init(1)"!(new chan1)chan1
chan1
(!("data(sinkChan)"(gnc). ProcData))  (('"data(sinkChan)". !("data(chan1)"(gnc). '"data(sinkChan)"))  ((new chan2)( '"init(2)"!. '"data(sinkChan)". !("data(chan2)"(gnc). '"data(sinkChan)"))))
chan1
(!("data(sinkChan)"(gnb). ProcData))  (((new chan1)( '"init(1)"!. '"data(sinkChan)". !("data(chan1)"(gnb). '"data(sinkChan)")))  ((new chan2)( '"init(2)"!. '"data(sinkChan)". !("data(chan2)"(gnb). '"data(sinkChan)"))))
broadcastscan unicast
▹
true

(!("data(sinkChan)"(gnc). ProcData))  (('"data(sinkChan)". !("data(chan1)"(gnc). '"data(sinkChan)"))  ((new chan2)( '"init(2)"!. '"data(sinkChan)". !("data(chan2)"(gnc). '"data(sinkChan)"))))
Data Collection
0
1 2
Sink
Node Node
tau
datum1
((ProcData)  (!("data(sinkChan)"(gnb). ProcData)))  ((!("data(chan1)"(gna). '"data(sinkChan)"))  ((new chan2)( '"init(2)"!. '"data(sinkChan)". !("data(chan2)"(gna). '"data(sinkChan)"))))
broadcastscan unicastunicasts
▹
true

Example Summary
• Structured channels • Broadcast and Unicast Communication • Broadcast Connectivity as an assertion • Parameters of Pwb for WSN

How to Implement an Instance

Supporting library of Solvers Nominal Parser Printer
Parametric Pwb Architecture
Psi Calculi Core
Symbolic Execution
Symbolic Equivalence Checker
etc.
Command Interpreter
Pwb

Supporting library of Solvers Nominal Parser Printer
Parametric Pwb Architecture
Psi Calculi Core
Symbolic Execution
Symbolic Equivalence Checker
Data
etc.
Logics Assertions
Execution Constraint Solver
Equivalence Constraint Solver
ParserPretty Printer Command Interpreter
User Supplied Pwb

Implementing the Example in Pwb
datatype term = Init of term
 Data of term  Name of name  Int of int
datatype condition = OutputConn of term * term
 InputConn of term * term  ChEq of term * term
datatype assertion = Top
Type of Data Type of Logic
Type of Assertions

datatype term = Init of term
 Data of term  Name of name  Int of int
datatype condition = OutputConn of term * term
 InputConn of term * term  ChEq of term * term
datatype assertion = Top
Type of Data
Type of Logic
Type of Assertions
Operationschaneq : term*term > condition
compose : assertion*assertion > assertion
brReceive : term*term > conditionbrTransmit : term*term > condition
substA : (name*term) list > A > Afor A in term, condition, assertion
Implementing the Example in Pwb

Execution Constraint Solversolve : condition list > (substitution*assertion) option
(simplified signature)
In the example solves a unification problem for unicast channels
In the example solves a membership problem in the connectivity graph for broadcast channels
e.g. ChEq (Data “sinkChan”, Data “sinkChan”)
Implementing the Example in Pwb
. P↵�!C
P 0

Easy to Obtain a ToolJust
Implement
datatype term
datatype condition
datatype assertion
chaneq : term*term > condition
compose : assertion*assertion > assertion
brReceive : term*term > condition
brTransmit : term*term > condition
substA : (name*term) list > A > Afor A in term, condition, assertion
solve : condition list > (substitution*assertion) option

Currently implemented Calculi (1)
• picalculus (260 + 333 LOC): data are names, logic of equality on names. Also includes a equivalence solver.
• Frame Hopping Spread Spectrum (292 LOC): structured data as channels, logic of equality on the data. Solver is implemented as unification.
• Common Ether (331 LOC): data are names, assertions are sets of names and logic of membership of a name in the current assertion. Solver generates assertions.

Currently implemented Calculi (2)
• The example WSN (462 LOC): as already discussed. • Aggregating WSN (569 LOC): similar to the example. The
instance extends it with structured data with the aggregation operator and positive integers with arithmetic operations.
• Alternating Bit Protocol (574 LOC): structured data with bit operations, substitution does term rewriting, logic is over equations of bit operations and bit predicates.
• Valuepassing CCS (538 LOC): structured data over a signature (of arithmetic), logic of linear equations, solver use an external linear programming solver.

Instance Summary
• All of the instances are done in the same tool Pwb • Don’t need separate tools • The calculi inherit machined checked proofs

Future Work
• Model Checking • Behavioral Preorder Checker • Behavioral Types • Modular Construction of
Instances
Functionality
• Bigger RealWorld Instances • Interfacing with Isabelle
(generating proofs)
• Higher Order Processes • Reliable Broadcast • Pattern Matching
Application
Extensions

Conclusions
• Pwb is a parametric tool on data and logics for concurrency
• Pwb is one tool for many calculi inheriting machine checked proofs
• Pwb provides primitives for both unicast and broadcast communication
• Pwb provides symbolic execution and equivalence checking

Where to Get Pwb
Pwb is free software (GPL)
http://goo.gl/ZJPu9 http://goo.gl/aU40h
Pwb on GithubPwb Home
Runs on UNIX like systems (on Windows, use cygwin)
http://goo.gl/ZJPu9http://goo.gl/aU40h