S90.20 Practice Questions

Question 1

Services A, B and C belong to Service Inventory A .Services D, E and F belong to Service Inventory B .Service C acts as an authentication broker for Service Inventory A .Service F acts as an authentication broker for Service Inventory B .Both of the authentication brokers use Kerberos-based authentication technologies. Upon receiving a request message from a service consumer, Services C and F authenticate the request using a local identity store and then use a separate Ticket Granting Service (not shown) to issue the Kerberos ticket to the service consumer. A recent security audit of the two service inventories revealed that both authentication brokers have been victims of attacks. In Service Inventory A, the attacker has been intercepting and modifying the credential information sent by Service C (the ticket requester) to the Ticket Granting Service. As a result, the requests have been invalidated and incorrectly rejected by the Ticket Granting Service. In Service Inventory B, the attacker has been obtaining service consumer credentials and has used them to request and receive valid tickets from the Ticket Granting Service. The attacker has then used these tickets to enable malicious service consumers to gain access to other services within the service inventory. How can the two service inventory security architectures be improved in order to counter these attacks?

Accepted Answer

The Data Confidentiality pattern can be applied to messages exchanged by the services in Service Inventory A .The Data Origin Authentication pattern can be applied to messages exchanged by services in Service Inventory B .

Answer

The Service Perimeter Guard pattern can be applied to Service Inventory A in order to establish a perimeter service responsible for validating and filtering all incoming request messages on behalf of Service C .The Data Origin Authentication pattern can be applied to messages exchanged by services in Service Inventory B .This will ensure the integrity of messages by verifying their origins to the message recipients.

Answer

WS-Secure-Conversation can be used to secure the communication between the authentication broker and service consumers in Service Inventory A .This ensures that Services A and B will contact Service C to request a security context token that will be used to generates a session key for the encryption of the ticket submitted to Service C . The Data Origin Authentication pattern can be applied to messages exchanged by services in Service Inventory B .This will ensure the integrity of messages try verifying their origins to the message recipients.

Answer

WS-Trust can be used to establish secure communication between the authentication broker and the service consumers. After receiving the request message and the corresponding credentials from service consumers, the authentication broker can validate their identity, and if successful, a signed SAML assertion containing all authentication information will be issued. The SAML assertion will then be used to authenticate the service consumers during subsequent communications. Because the messages are signed and encrypted, malicious service consumers cannot access the data. This approach can be applied to counter the threats in both Service Inventories A and B .

Question 2

Service A provides a data retrieval capability that can be used by a range of service consumers, including Service Consumer A, In order to retrieve the necessary data. Service Consumer A first sends a request message to Service A (1). Service A then exchanges request and response messages with Service B (2, 3). Service C (4, 5), and Service D (6. 7). After receiving all three response messages from Services B .C .and D, Service A assembles the collected data into a response message that it returns to Service Consumer A (8). The Service A data retrieval capability has been suffering from poor performance, which has reduced its usefulness to Service Consumer A .Upon studying the service composition architecture, it is determined that the performance problem can be partially attributed to redundant validation by service contracts for compliance to security policies. Services B and C have service contracts that contain the same two security policies. And, Service D has a service contract that contains a security policy that is also part of Service A's service contract. What changes can be made to the service contracts in order to improve the performance of the service composition while preserving the security policy compliance requirements?

Accepted Answer

Apply the Policy Centralization pattern in order to establish two centralized policy definitions and ensure that policy enforcement logic is correspondingly centralized. The first policy definition includes the redundant security policies from Services A and D and the second policy definition contains the redundant security policies from Services B and C .

Answer

Apply the Policy Centralization pattern in order to establish a single security policy for the entire service composition. The-redundant policies residing in the service contracts of Services A .B, C and D need to be removed and grouped together into one master policy definition enforced by Service A .This way, redundant policy validation is eliminated, thereby improving runtime performance.

Answer

All policies are analyzed for similarities, which are then extracted and, by applying the Policy Centralization pattern, combined into a single policy definition. This 'meta-policy' is then positioned to perform validation of the response message generated by Service A, prior to receipt by Service Consumer A .If validation fails, an alternative error message is sent to Service Consumer A instead.

Answer

Apply the Standardized Service Contract principle in order to remove redundancy within service contracts by ensuring that all four service contracts comply with the same policy standards. This further requires the application of the Service Abstraction principle to guarantee that policy definitions are sufficiently streamlined for performance reasons.

Question 3

Service Consumer A sends a request message to Service A (1), after which Service A sends a request message to Service B (2). Service B forwards the message to have its contents calculated by Service C (3). After receiving the results of the calculations via a response message from Service C (4), Service B then requests additional data by sending a request message to Service D (5). Service D retrieves the necessary data from Database A (6), formats it into an XML document, and sends the response message containing the XML-formatted data to Service B (7). Service B appends this XML document with the calculation results received from Service C, and then records the entire contents of the XML document into Database B (8). Finally, Service B sends a response message to Service A (9) and Service A sends a response message to Service Consumer A (10). Services A, B and D are agnostic services that belong to Organization A and are also being reused in other service compositions. Service C is a publicly accessible calculation service that resides outside of the organizational boundary. Database A is a shared database used by other systems within Organization A and Database B is dedicated to exclusive access by Service B .Service B has recently been experiencing a large increase in the volume of incoming request messages. It has been determined that most of these request messages were auto-generated and not legitimate. As a result, there is a strong suspicion that the request messages originated from an attacker attempting to carry out denial-of-service attacks on Service B .Additionally, several of the response messages that have been sent to Service A from Service B contained URI references to external XML schemas that would need to be downloaded in order to parse the message data. It has been confirmed that these external URI references originated with data sent to Service B by Service C .The XML parser currently being used by Service A is configured to download any required XML schemas by default. This configuration cannot be changed. What steps can be taken to improve the service composition architecture in order to avoid future denial-of-service attacks against Service B and to further protect Service A from data access-oriented attacks?

Accepted Answer

Apply the Data Origin Authentication pattern so that Service B can verify that request messages that claim to have been sent by Service A actually did originate from Service A .Apply-the Message Screening pattern to add logic to Service A so that it can verify that external URIs in response messages from Service B refer to trusted sources.

Answer

Apply the Service Perimeter Guard pattern to establish a perimeter service between Service B and Service C .Apply the-Brokered Authentication pattern by turning the perimeter service into an authentication broker that is capable of ensuring that only legitimate response messages are being sent to Service C from Service B Further apply the Data Origin Authentication pattern to enable the perimeter service to verify that messages that claim to have been sent by Service C actually originated from Service C .Apply the Message Screening pattern to add logic to the perimeter service to also verify that URIs in request messages are validated against a list of permitted URIs from where XML schema downloads have been pre-approved.

Answer

Apply the Service Perimeter Guard pattern and the Message Screening pattern together to establish a service perimeter guard that can filter response messages from Service C before they reach Services A and B .The filtering rules are based on the IP address of Service C .If a request message originates from an IP address not listed as one of the IP addresses associated with Service C .then the response message is rejected.

Answer

Apply the Direct Authentication pattern so that Service C is required to provide security credentials, such as Username tokens, with any response messages it sends to Service B .Furthermore, add logic to Service A so that it can validate security credentials passed to it via response messages from Service B .by using an identity store that is shared by Services A and B .

Question 4

Service Consumer A submits a request message with security credentials to Service A (1). The identity store that Service A needs to use in order to authenticate the security credentials can only be accessed via a legacy system that resides in a different service inventory. Therefore, to authenticate Service Consumer A, Service A must first forward the security credentials to the legacy system (2). The legacy system then returns the requested identity to Service A (3). Service A authenticates Service Consumer A against the identity received from the legacy system. If the authentication is successful, Service A retrieves the requested data from Database A (4), and returns the data in a response message sent back to Service Consumer A (5). Service A belongs to Service Inventory A which further belongs to Security Domain A and the legacy system belongs to Service Inventory B which further belongs to Security Domain B .(The legacy system is encapsulated by other services within Service Inventory B, which are not shown in the diagram.) These two security domains trust each other. Communication between Service A and the legacy system is kept confidential using transport-layer security. It was recently discovered that a malicious attacker, posing as Service Consumer A, has been accessing Service A .An investigation revealed that these attacks occurred because security credentials supplied by Service Consumer A were transmitted in plaintext. Furthermore, vulnerabilities to replay attacks and malicious intermediaries have been detected. Which of the following statements describes a solution that can counter these types of attacks?

Also, list the industry standards required by the proposed solution.

Accepted Answer

Apply the Data Origin Authentication pattern together with the Data Confidentiality pattern in order to establish message-layer security that guarantees the confidentiality and integrity of messages exchanged by Service Consumer A and Service A .Further, a security policy can be created to require that security credentials submitted to Service A must be digitally signed and encrypted and also contain a timestamp to validate the actual time the request was issued. Industry standards that can be used for this solution are WS-Policy, WS-Security-Policy, XMLEncryption, and XML-Signature.

Answer

Apply the Service Perimeter Guard pattern together with the Trusted Subsystem pattern to establish a perimeter service that can perform security functions on behalf of Service A .Theutility service can verify the validity of the request messages from Service Consumer A by authenticating the request message against an identity store. If the request message is authenticated, the utility service then sends it to Service A for further processing. All communications between Service A and Service Consumer A can be encrypted using the public key of the intended recipient, and signed using the private key of the sender. Industry standards that can be used for this solution are XML-Encryption, XML-Signature, and WS-Trust.

Answer

Apply the Service Perimeter Guard pattern to establish a perimeter service that can perform security functions on behalf of-Service A .Next, apply the Data Confidentiality pattern so that the security credential information provided by Service Consumer A with the request message is encrypted with the secret key shared between the perimeter service and Service Consumer A .The perimeter service evaluates the credentials and if successfully authenticated, forwards the request message to Service A .Transport-layer security is used to protect message exchanges between Service A and Service Consumer A .

Answer

Apply the Trusted Subsystem pattern together with the Data Origin Authentication pattern in order to establish a utility service-that performs the security processing on behalf of Service A .Service Consumer A must digitally sign all request messages and encrypt the credential information using the public key of the utility service. The utility service can then verify the security credentials and the digital signature to establish the validity of the request message. If the request message is permitted, the utility service establishes a composite trust domain that encompasses Service Consumer A, Service A, Database A, and the legacy system. Because all communications remain within a single trust domain, malicious intermediaries will not be able to gain access to any exchanged data.

Question 5

Service Consumer A sends a request message to Service A (1) after which Service A retrieves financial data from Database A (2). Service A then sends a request message with the retrieved data to Service B (3). Service B exchanges messages with Service C (4) and Service D (5), which perform a series of calculations on the data and return the results to Service A .Service A uses these results to update Database A (7) and finally sends a response message to Service Consumer A (8). Component B has direct, independent access to Database A and is fully trusted by Database A .Both Component B and Database A reside within Organization A .Service Consumer A and Services A, B, C, and D are external to the organizational boundary of Organization A .Service A has recently experienced an increase in the number of requests from Service Consumer A .However, the owner of Service Consumer A has denied that Service Consumer A actually sent these requests. Upon further investigation it was determined that several of these disclaimed requests resulted in a strange behavior in Database A, including the retrieval of confidential data. The database product used for Database A has no feature that enables authentication of consumers. Furthermore, the external service composition (Services A, B, C, D) must continue to operate at a high level of runtime performance. How can this architecture be improved to avoid unauthenticated access to Database A while minimizing the performance impact on the external service composition?

Accepted Answer

A utility service is established to encapsulate Database A and to carry out the authentication of all access to the database by Service A and any other service consumers. To further support this functionality within the utility service, an identity store is introduced. This identity store is also used by Service A which is upgraded with its own authentication logic to avoid access by malicious service consumers pretending to be legitimate service consumers. In order to avoid redundant authentication by services within the external service composition, Service A creates a signed SAML assertion that contains the service consumer's authentication and authorization information.

Answer

Service Consumer A generates a pair of private/public keys (Public Key E and Private KeyD) and sends the public key to-Service A .Service A can use this key to send confidential messages to Service Consumer A because messages encrypted by the public key of Service Consumer A-can only be decrypted by Service A The Data Origin Authentication pattern can be further applied so that Service A can authenticate Service Consumer A by verifying the digital signature on request messages. The Message Screening pattern is applied to a utility service that encapsulates Database A in order to prevent harmful input.

Answer

The Brokered Authentication pattern is applied so that each service consumer generates a pair of private/public keys and sends the public key to Service A .When any service in the external service composition (Services A, B, C, and D) sends a request message to another service, the request message is signed with the private key of the requesting service (the service acting as the service consumer). The service then authenticates the request using the already established public key of the service consumer. If authentication is successful, the service generates a symmetric session key and uses the public key of the service consumer to securely send the session key back to the service consumer. All further communication is protected by symmetric key encryption. Because all service consumers are authenticated, all external access to Database A is secured.

Answer

Implement a firewall between Service Consumer A and Service A .All access to Service A is then controlled by the firewall rules. The firewall contains embedded logic that authenticates request messages and then forwards permitted messages to Service A .Moreover, the firewall can implement the Message Screening pattern so that each incoming message is screened for malicious content. This solution minimizes the security processing performed by Service A in order to maintain the performance requirements of the external service composition.

Free Arcitura Education S90.20 Exam Practice Questions & Explanations