A Heuristic Approach for Secure Service Composition Adaptation

Liverpool John Moores UniversityBo Zhou

B.Zhou@ljmu.ac.uk

OverviewSOA and its security issues

Secure service composition adaptation

0/1 knapsack problem

Heuristic solution

Simulated annealing

Service-oriented ArchitectureFoundation for modelling, planning,

searching for and composing services.

Offer new applications via composition of services.

Facilitated by standardised interoperations among services.- WSDL, USDL, BPMN

A BPMN example

Security measures in SOAVerification is to ensure selected services comply

with the security policy at both design- and run-time.- Changes in service behaviour or operating context

could affect the stated composition behaviour.- There are variety of existing tools for performing

analysis of individual or composed services. i.e. formal analysis and code analysis

Inconsistent security policies and configurations must be continually monitored and addressed.- Countermeasures such as adaptation or recomposition.

Secure Service Composition AdaptationComposition adaptation aims to mitigate issues identified during

verification and monitoring.

Adaptation is not straightforward due to the following reasons.- No direct suggestions from verification tools.- Concept of security is broad.- A simple substitution of a service may result in dramatic changes to

the security properties of the entire composition.

Individual success does not guarantee collective satisfactory. - For example, two services use different encryption algorithms.

The secure composition adaptation issue is actually an optimisation problem with constraints.- Especially when facing wide choice of alternatives.

The 0/1 Knapsack Problem

Given a set of items, each with a weight and a value, determine the items to be included in a combination so that the total weight is less than or equal to a given limit (e.g. the capacity of a knapsack) and the total value is as large as possible.

The 0/1 Knapsack Problem

Similarity to our problemDefinition- Given a set of alternative services, what

is the best combination of them in order to achieve the most secure service composition?

There are always constraints while selecting services.- On trustworthiness, running efficiency and many other

QoS and security related factors. - This is known as the 0/1 multidimensional knapsack

problem.Focus on typical business decision where the user

has to balance security withcost.Cost->Weight Security->Value

Optimisation of Composition Adaptation

C

S1?

S11

S12

S13

S2?

S21

S22

Sn?

Sn1

Sn2

Snm

Candidate Services

ServiceCompositi

on

Composition plan

Heuristics-based SolutionProblems that have no polynomial-time

algorithms are known for solving them.- NP-complete

Exhaustive search is impractical.- Formal verification is a time consuming and

resource wasting processHeuristic methods select compositions

`intelligently‘, attempting to find increasingly successful solutions until an adequate answer is found.- Aiming for fast and accurate adaptation.

Simulated AnnealingUsed to solve NP-complete problems in

general, including 0/1 knapsack problem.

Named to mimic the chemical process when atoms in metal become placed in relative order during the process of being overheated to gradually being cooled.

The solution1. Choose any feasible combination randomly.2. Randomly select an item from the original items set n.3. If the item has not been collected, add the item to the combination. If the

new combination does not satisfy the weight constraint, randomly remove an item from the combination until it becomes feasible.

4. While in step 3 if the item has already been collected, remove this item and pick up another item from the items set that forms a new feasible combination.

5. If the new combination satisfies following equation, than the new combination will be accepted.

where ΔV represents the change of value, T is the temperature, e is the mathematical constant and R(0, 1) generates a random number between 0 and 1.

6. For the value function V, if ΔV is a positive, that means the new combination has greater value and the equation is always true; if ΔV is negative, than the new combination has lower value. However, it is still possible that the new combination will be accepted. In effect, with larger T, the chance of satisfying the equation is higher.

7. Repeat steps 2-6 several times, decreasing the value of T at each step until a lower threshold for the value of T is reached.

8. When T reaches the threshold value, the current solution will be the best one we can get.

R(0,1) > e T

V

Quantify ServicesTo apply the solution, we have to find away to quantify

services.- Will allow direct comparison of services.

Current proposal is to derive the security properties from service level agreement and catogorise them into four aspects.- Privacy, Confidentiality, Authenticity, Availability.- For example, `secured communication = true‘ contributes 0.5 to

Confidentiality and 0.3 to Privacy; `encryption algorithm = 3DES‘ contributes another extra 0.1 to Confidentiality.

e.g. S = 0.4 × C + 0.2 × U + 0.1 × V + 0.3 × P

where C represents the value of Confidentiality, U represents Authenticity, V represents Availability and P represents Privacy.

Future WorkProve the NP-completeness

Examine the efficiency of Heuristics solutions- Adaptation speed and accuracy- Other solutions apart from Simulated

Annealing

SummarySOA and its security issueSecure Service Composition AdaptationNP-complete with 0/1 knapsack problemHeuristic solutions such as Simulate

Annealing

Q & A