Web Services and the Semantic Web:Open Discussion Session

Diana Geangalau

Ryan Layfield

OASIS

http://www.oasis-open.org/home/index.php Web Services are a way of implementing service-

orientation architecture Supposed to be Internet-based XML-oriented More than just connecting web pages

• Must be structure behind them• Self-contained (i.e. self-describing)

What was the original intention of it? How do they treat the security issues in service-

oriented architecture? Helps to resolve contradicting standards among

multiple needs

OASIS

OASIS

WS security as enhancements to SOAP messaging to provide message integrity and confidentiality.

Requirements:Multiple security token formatsMultiple trust domainsMultiple signature formatsMultiple encryption technologiesEnd-to-end message content security and not

just transport-level security

OASIS

ConceptsSecurity TokensSignatures

Security ConcernsConfidentiality: EncryptionIntegrity: Signature

Policy Definition Location

OASIS

SignaturesProvide a way for the recipients to verify

the integrity of the messageSign the important parts of the messageTo verify if the policies of a security token

apply to the sender

OASIS

Is the security policy specified only once?

R: No. Security policy can be targeted for the destination as well as for any intermediary therefore can be present a number of times in the SOAP message once for each target (multiple headers).

OASIS

Can you have multiple signatures attached to a message?

R: Yes. Multiple signatures can reference different or overlapping parts of the message, reason being in distributed applications messages usually go through multiple processing stages (workflow).

OASIS

Can you see the issues involved with multiple processing stages?

R: There are issues with the signatures for important parts of the message that need to be legitimately altered during the various stages of processing.

OASIS

EncryptionCan encrypt header blocks, body blocks,

or part of themCommon symmetric key shared by the

sender and the receiverEncrypted symmetric key inside the

message

OASIS

Can you have overlapping encryption for parts of message? Why? In which order should they be encrypted?

R: Yes. Because the decryption might be done in the different stages of processing. The order has to be predefined by prior agreement.

OASIS

Can you think what “freshness” of security semantics means?

R: If security semantics are “old”, they might be ignored by the receiver. Need to specify time references but the specification does not provide a mechanism for synchronizing time.

OASIS

Where would you specify the time references?

R: XML Schema (web services are XML based).

SAML

Security Assertion Markup LanguageDesigned to provide a single point of

authorizationAims to ‘solve the web single sign-on’ problemOne identity provider in group allows access

Public/Private Key Foundation Competitors

Microsoft PassportOpenID (VeriSign)Global Login System (Open Source)

SAML

Three main components (from http://searchwebservices.techtarget.com/ tip/1,289483,sid26_gci818643,00.html ) Assertions: SAML has three kinds of assertions.

Authentication assertions are those in which the user has proven his identity. Attribute assertions contain specific information about the user, such as his spending limits. Authorization decision assertions identify what the user can do, for example, whether he can buy an item.

Protocol: This defines the way that SAML asks for and gets assertions, for example, using SOAP over HTTP for now, although using other methods in the future.

Binding: This details exactly how SAML message exchanges are mapped into SOAP exchanges.

SAML

Do you think SOAP is an efficient platform for security?

SAML

Are you comfortable knowing that part of your security implementation was written by the community? (Open-source)

SAML

How do you think we should handle multiple system types across a network? Do you think we need a new protocol to address this, or should SAML be expanded? (Federations)

SAML

How do we deal with older systems that don’t support this protocol with those that do?

SAML

Outstanding Issues Performance

• No Caching• Text-based transfer• Does not specify encryption (policies may be compromisable)• Binary must be encoded in Base64• Must be implemented over HTTP protocol via SOAP

Ownership• Sun developed large amount of it (via OpenSAML)• Claims it will not assert ownership• What happens if they do?

Federations• Authentication protcols not specified• Multiple domains are an issue• SAML 2.0 supposed to address this; will it be at the cost of becoming

monolithic? Legacy Applications

• Very expensive to retro-fit

XACML

eXtensible Access Control Markup Language

Highlights (from OASIS): Combines multiple rules into a single policyPermit multiple users to have different rolesProvide separation between policy writing and

application environment

Ultimately standardizes access control languages

XACML

Users interact with resources Every resource is protected by an entity

known as a Policy Enforcement Point (PEP)This is where the language is actually usedDoes not actually determine access

PEP sends it’s request to a Policy Decision Point (PDP)Policies may or may not be actually stored hereMakes the final say on access

Decision is relayed to PEP, which then grants or denies access

XACML

Do you think a system is more secure or less secure when it is distributed across multiple computers? What about a single system responsible for all?

XACML

How would you feel if you were using work that a corporation gave on it’s word on alone that it would never assert the rights to it?

XACML

Should policies be self-contained, or is it OK for them to reference each other? Is cross-PDP communication safe?

XACML

Outstanding Issues Distributed Responsibility

• What happens when the PEP is responsible for multiple objects? • What happens when we can compromise the PDP or spoof it’s

communication?• How do we guarantee that we reference the right object?• While the system is distributed, a policy is still in only one location

Ownership• Contributors like Sun have again done work in this area• Same as with SAML

Policy Cross-Referencing • One policy may access another• Typical issues arrise as with inheritance and unions/intersections of

related work• How do we deal with conflicts?

References

Sun’s XACML Documentation: http://sunxacml.sourceforge.net/guide.html

OpenSAML: http://www.opensaml.org/ OASIS: http://www.oasis-open.org/home/index.php Wikipedia’s Entry on SAML:

http://en.wikipedia.org/wiki/SAML

Questions

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