1. ASPIRE: Automated Systematic Protocol Implementation Robustness Evaluation

2. CONTENT
Introduction
Definitions & Taxonomy of Application Layer Protocols
Fault Generation Algorithms
Experiments & Conclusions

3. Introduction
Robustness – Ability of an implementation to handle exceptional input in the form of faulty PDUs and continue normal protocol operation
Protocol implementations differ in their behavior on faulty inputs
Challenge in automated robustness protocol testing is systematic generation of faulty inputs
Taxonomy of Application layer protocols used to design test cases for testing robustness

4. Defnitions PDU : <c1,…cn>; ci = control fields
Protocol Specification: Defines syntax, semantics and allowed sequences of PDUs
Protocol Implementation: P={Si|Si=[<p1,h1,a1>….<pn,hn,an>]}; P=set of sequences, each triple<pi, hi, ai> represents an action ai (send or receive) on PDU pi by host hi

5. Taxonomy of Application Layer Protocols
Stateless Protocols - HTTP: State information about a client (record of transaction) is not maintained; susceptible to syntactical faulty PDUs
Stateful Protocols – SMTP: State information about a client until the transaction is over is maintained; susceptible to semantic faulty PDUs

6. Fault Generation Algorithms
Generating syntactically faulty PDUs : Maximally faulty PDUs grow exponentially in the number of fields – Pruning Strategy (pair wise testing constraint)
Generating semantically faulty PDUs : Semantic faulty PDUs grow polynomially (manageable); Test case consists of a state, list of semantically faulty PDUs related to that state and sequence of correct PDUs which will drive the protocol to that state

7. Experiments & Conclusions
Evaluated Hypotheses:
- Protocol implementations differ in their behavior in terms of robustness to faulty PDU input for both stateful & stateless protocols
- Pair wise constraint in the pruning strategy does not reduce the capacity to evaluate robustness of different implementations

8. Metrics
-Reduced ratio = syntactic faulty PDUs by the generation algorithm / combinatorial enumeration
- Robustness ratio = number of faulty inputs that were handled by implementation by continuing normal operation / total number of faulty inputs
Results show the following to prove the hypotheses:
Average robustness ratio is not different for syntactic faulty PDUset of all posssible faulty PDUs
Average robustness ratio of different implementations is different for semantic & syntactic faults

9. Thank You