Security in semantic web

Hassan Abolhassani, Leila SharifSharif university of technology

abolhassani@sharif.ir

Outline

● Semantic Web: a short introduction ● Security model in html document based web● Security issues in a sample semantic web● Analysis of solutions

● Query reformulation: centralized version● Query reformulation: distributed version● Security aware inference engine

Semantic web

● Bringing meaning to the web● Overcome the limitation of current web

– Machine processing is not possible– Search engines returns a lot of un-related

results● Impossible using current web:

– Find information about animals that use sonar but are not either bats or dolpines

– Finding (best) prices of goods and services– Delegating task to agents: Book me a holiday

next weekend somewhere warm not too far away

Syntatic web

Semantic web layers

Semantic web layers

Focus of this work

Outline

● Semantic Web: a short introduction ● Security model in html document based web● Security issues in a sample semantic web● Analysis of solutions

● Query reformulation: centralized version● Query reformulation: distributed version● Security aware inference engine

Simplified security model of the current web

● A page as a whole is subject to security● All the concepts in a page is treated equally● Searches return references to pages, not to concepts● This model is not applicable to semantic web

Outline

● Semantic Web: a short introduction ● Security model in html document based web● Security issues in a sample semantic web● Analysis of solutions

● Query reformulation: centralized version● Query reformulation: distributed version● Building security aware inference engine

A sample semantic web

● company1 has name1 as its name ● person1 is the president of the company1● this person has phone1 as his personal phone and phone2 as his office phone● the company has partner1 as one of its partners● partner1 has product1 with name1 and price1 as its name and price respectively● ...

A sample semantic web (cont.)

Example queries (in OWL/QL)● Finding the “personalPhone” number of the president of “company1”:

Query: (“What is the personalPhone of president of company1”)

Query Pattern: {(c:president company1 ?person) (p:personalPhone ?person ?phone)}

Must-Bind Variables List: (?phone)

May-Bind variables List: ()

Don't-Bind Variables List: ()

Answer Pattern: {(p:personalPhone “president of company1” ?phone)}

Example queries (in OWL/QL)● Finding the “personalPhone” number of the president of “company1”:

Query: (“What is the personalPhone of president of company1”)

Query Pattern: {(c:president company1 ?person) (p:personalPhone ?person ?phone)}

Must-Bind Variables List: (?phone)

May-Bind variables List: ()

Don't-Bind Variables List: ()

Answer Pattern: {(p:personalPhone “president of company1” ?phone)}

Is anybody's access to personal phone number of presidentof company ok?

Example queries (in OWL/QL)● Finding a provider company that provides product1

Query: (“What partner provides product1”)

Query Pattern: {(c:partner company1 ?partner) (c:product ?partner prd:product1)}

Must-Bind Variables List: (?partner)

May-Bind variables List: ()

Don't-Bind Variables List: ()

Answer Pattern: {(prd:prduct ?partner prd:product1)}

Example queries (in OWL/QL)● Finding a provider company that provides product1

Query: (“What partner provides product1”)

Query Pattern: {(c:partner company1 ?partner) (c:product ?partner prd:product1)}

Must-Bind Variables List: (?partner)

May-Bind variables List: ()

Don't-Bind Variables List: ()

Answer Pattern: {(prd:prduct ?partner prd:product1)}

Is anybody's access to partner information ok?

Differences between traditional web and semantic web security

● Concepts are linked not web pages● Query instead of search● A query processor traverses a semantic web graph● For each node in the graph a different access

previlage may be assigned● We don't want to repeat current web limitations

● Each different site has its own logon facility● Single sign-on is introduced to solve this

● How to add security to SW?

Outline

● Semantic Web: a short introduction ● Security model in html document based web● Security issues in a sample semantic web● Analysis of solutions

● Query reformulation: centralized version● Query reformulation: distributed version● Building security aware inference engine

Ad-hoc solution

● Create several semantic webs:● Separate non-public and public information

● This works but is not a general solution:● Results in redundant information: creation,

maintenamce, and other problems.● It is not feasible when we have a distributed

model (query processor should know about all security measures of involving sites)

Query reformulation (filtering)

● Using OWL/QL features of variable binding

Query reformulation (cont.)

● Merits:● Easy to implement● Has not a significant overhead on query

processing● Demerits

● Not applicable when a semantic model is distributed

Distributed query reformulation

Query pattern

Query processor

Site1 filteringagent

Site2 filteringagent

SiteN filteringagent

Query pattern

Filtered Query pattern

Distributed query reformulation (cont.)

● Merits:● No centeralized control on security is needed● Applicable to semantic webs that are distributed

● Demerits● Overhead of pre-prossesing● The need for filtering agents at each site● May introduce security holes (should be

investigated further)

Security aware inference engines

● It is clear by now that the general solution is to add security at the level of inference engines

● To have a security model we need to have a formalism

● The basic formal model for SW is considered to be Description logic:● A variable-free logic formalism● A deciedable fragment of first-order logic● All constructs are convertible to first-order logic

unary and binary predicate

Security aware inference engines (cont.)

● Basic description logic AL (attributive language) description logic:

Sample statements:

Security aware inference engines (cont.)

● Inference in Description Logic● Tableau based reasoning algorithms has been

developed● This algorithms work based on expansion

(completion) rules● A tree is expanded starting from the original

statement (i.e. Query)● Algorithm stops when a clash appears (i.e. C and

~C in the same node)

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Example of inference

Security aware inference engines (cont.)

● Expansion rules for ALC

Security aware inference engines (cont.)

● Adding security semantics to expansion rules

Security aware inference engines (cont.)

● Security added tableau algorithm

● Output of reasoner depends on the way the processing is terminated:● In case of a clash the output can be something like: The query is

not answerable by the knowledge base● In case of a security violation: You are not allowed to

traverse parts of knowledge base needed to respond to your query

apply completion rules in arbitrary order as long as possible:- stop in case of clash- stop in case of “security violation”- Terminate if no completion rule is applicable

Security aware inference engines (cont.)

● Merits:● An algorithm based on a formal language● Complexity is same as tableau

● Demerits● ?

Conclusions

● Differences between security model of syntactic web and semantic web is recognized

● Several solutions proposed:● Ad-hoc: applicable to small closed organizations● Centeralized filtering: applicable to a small

society of organizations● Distributed filtering: applicable to any society of

organizations but with preprocessing overhead● Security aware inference engines: no limitations

upto now is recognized

Thank you