SOA S90.20 問題集

質問 1：
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?
A. Service Consumer A generates a pair of private/public keys (Public Key E and Private Key D) 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.
B. 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.
C. 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.
D. 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.
正解：B

質問 2：
Services A, B, and C reside in Service Inventory A and Services D, E, and F reside in Service Inventory B.
Service B is an authentication broker that issues WS-Trust based SAML tokens to Services A and C upon receiving security credentials from Services A and
C. Service E is an authentication broker that issues WS-Trust based SAML tokens to Services D and F upon receiving security credentials from Services D and E.
Service B uses the Service Inventory A identify store to validate the security credentials of Services A and C.
Service E uses the Service Inventory B identity store to validate the security credentials of Services D and F.

To date, the two service inventories have existed independently from each other. However, a requirement has emerged that the services in Service Inventory A need to be able to use the services in Service Inventory B, and vice versa.
How can cross-service inventory message exchanges be enabled with minimal changes to the existing service inventory architectures and without introducing new security mechanisms?
A. The Trusted Subsystem pattern is applied to encapsulate Services B and E using a central utility service that balances request and response messages exchanged between Services B and E, depending on which service inventory the messages originate from. The utility service also contains transformation logic to ensure that the SAML tokens issued by Services B and E are compatible. This guarantees that an issued SAML token can be used across Service Inventories A and B without further need for runtime conversion.
B. The individual domain service inventories need to be combined into one enterprise service inventory. The Service Perimeter Guard pattern can be applied to establish a contact point for request messages originating from outside the service inventory. Within the service inventory, services no longer need to be authenticated because they are all part of the same trust boundary.
C. Because SAML tokens cannot be used across multiple security domains, authentication brokers C and E need to be replaced with one single authentication broker so that one token issuer is used for all services across both of the service inventories.
D. The current security mechanism already fulfills the requirement because SAML tokens can be used across multiple security domains. The only change required is for each authentication broker to be configured so that it issues service inventory-specific assertions for SAML tokens originating from other service inventories.
正解：D

質問 3：
Service A exchanges messages with Service B multiple times during the same runtime service activity. Communication between Services A and B has been secured using transport-layer security. With each service request message sent to Service B (1A. IB), Service A includes an X.509 certificate, signed by an external Certificate Authority (CA).
Service B validates the certificate by retrieving the public key of the CA (2A. 2B) and verifying the digital signature of the X.509 certificate. Service B then performs a certificate revocation check against a separate external CA repository (3A, 3B). No intermediary service agents reside between Service A and Service B.

Service B has recently suffered from poor runtime performance plus it has been the victim of an access-oriented attack. As a result, its security architecture must be changed to fulfill the following new requirements: 1. The performance of security-related processing carried out by Service B when communicating with Service A must be improved. 2. All request messages sent from Service A to Service B must be screened to ensure that they do not contain malicious content.
Which of the following statements describes a solution that fulfills these requirements?
A. Eliminate the need to retrieve the public key from the Certificate Authority and to verify the certificate revocation information by extending the service contract of Service B to accept certificates only from pre-registered Certificate Authorities. This form of pre- registration ensures that Service B has the public key of the corresponding Certificate Authority.
B. Apply the Trusted Subsystem pattern to by introducing a new utility service. Because Service B is required to limit the use of external resources. Service A must ensure that no other services can request processing from Service B in order to prevent malicious content from infiltrating messages. This is achieved by creating a dedicated replica of Service B to be used by the utility service only. Upon receiving the request message and the accompanying security credentials from Service A.
the utility service verifies the authentication information and the validity of the X.509 signature. If the authentication information is correct, then the utility service replicates the code of Service B, performs the necessary processing, and returns the response to Service A.
C. Apply the Trusted Subsystem pattern by introducing a new utility service between Service A and Service B.
When Service A sends request messages, the utility service verifies the provided credentials and creates a customized security profile for Service A.
The security profile contains authentication and access control statements that are then inherited by all subsequent request messages issued by Service A.
As a result, performance is improved because Service A does not need to resubmit any additional credentials during subsequent message exchanged as part of the same runtime service activity. Furthermore, the utility service performs message screening logic to filter out malicious content.
D. Add a service agent to screen messages sent from Service A to Service B.
The service agent can reject any message containing malicious content so that only verified messages are passed through to Service B.
Instead of using X.509 certificates, use WS- SecureConversation sessions. Service A can request a Security Context Token (SCT) from a Security Token Service and use the derived keys from the session key to secure communication with Service B.
Service B retrieves the session key from the Security Token Service.
正解：D