SOA S90.20 問題集

質問 1：
Service A has two specific service consumers, Service Consumer A and Service Consumer B (1). Both service consumers are required to provide security credentials in order for Service A to perform authentication using an identity store (2). If a service consumer's request message is successfully authenticated, Service A processes the request by exchanging messages with Service B (3) and then Service C (4). With each of these message exchanges, Service A collects data necessary to perform a query against historical data stored in a proprietary legacy system. Service A's request to the legacy system must be authenticated (5). The legacy system only provides access control using a single account. If the request from Service A is permitted, it will be able to access all of the data stored in the legacy system. If the request is not permitted, none of the data stored in the legacy system can be accessed. Upon successfully retrieving the requested data (6), Service A generates a response message that is sent back to either Service Consumer A or B.
The legacy system is also used independently by Service D without requiring any authentication. Furthermore, the legacy system has no auditing feature and therefore cannot record when data access from Service A or Service D occurs. If the legacy system encounters an error when processing a request, it generates descriptive error codes.

This service composition architecture needs to be upgraded in order to fulfill the following new security requirements: 1. Service Consumers A and B have different access permissions and therefore, data received from the legacy system must be filtered prior to issuing a response message to one of these two service consumers. 2. Service Consumer A's request messages must be digitally signed, whereas request messages from Service Consumer B do not need to be digitally signed.
Which of the following statements describes a solution that fulfills these requirements?
A. The Trusted Subsystem pattern is applied by introducing a utility service that encapsulates the legacy system. To support access by service consumers issuing request messages with and without digital signatures, policy alternatives are added to Service A's service contract. Service A authenticates the service consumer's request against the identity store and verifies compliance to the policy. Service A then creates a signed SAML assertion containing an authentication statement and the authorization decision. The utility service inspects the signed SAML assertions to authenticate the service consumer and then access the legacy system using a single account. The data returned by the legacy system is filtered by the utility service, according to the information in the SAML assertions.
B. The Trusted Subsystem pattern is applied by introducing a utility service that encapsulates the legacy system. Two different policies are created for Service A's service contract, only one requiring a digitally signed request message. The utility service accesses the legacy system using the single account. Service A authenticates the service consumer using the identity store and, if successfully authenticated, Service A send a message containing the service consumer's credentials to the utility service. The identity store is also used by the utility service to authenticate request messages received from Service A.
The utility service evaluates the level of authorization of the original service consumer and filters data received from the legacy system accordingly.
C. The Trusted Subsystem pattern is applied together with the Message Screening pattern by introducing a utility service that encapsulated the legacy system and contains message screening logic. First, the utility service evaluates the incoming request messages to ensure that it is digitally signed, when necessary. After successful verification the request message is authenticated, and Service A performs the necessary processing. The data returned from the legacy system is filtered by the utility service's message screening logic in order to ensure that only authorized data is returned to Service Consumers A and B.
D. The Trusted Subsystem pattern is applied by introducing a utility service that encapsulates the legacy system. After successful authentication, Service A creates a signed SAML assertion stating what access level the service consumer has. The utility service inspects the signed SAML assertion in order to authenticate Service A.
The utility service accesses the legacy system using the account information originally provided by Service Consumer A or B.
The utility service evaluates the level of authorization of the original service consumer and filters data received from the legacy system accordingly.
正解：A

質問 2：
Service A provides a customized report generating capability. Due to infrastructure limitations, the number of service consumers permitted to access Service A concurrently is strictly controlled. Service A validates request messages based on the supplied credentials (1). If the authentication of the request message is successful, Service A sends a message to Service B (2) to retrieve the required data from Database A (3). Service A stores the response from Service B (4) in memory and then issues a request message to Service C (5). Service C retrieves a different set of data from Database A (6) and sends the result back to Service A (7). Service A consolidates the data received from Services B and C and sends the generated report in the response message to its service consumer (8).

This service composition was recently shut down after it was discovered that Database A had been successfully attacked twice in a row. The first type of attack consisted of a series of coordinated request messages sent by the same malicious service consumer, with the intention of triggering a range of exception conditions within the database in order to generate various error messages. The second type of attack consisted of a service consumer sending request messages with malicious input with the intention of gaining control over the database server. This attack resulted in the deletion of database records and tables. An investigation revealed that both attacks were carried out by malicious service consumers that were authorized.
How can the service composition security architecture be improved to prevent these types of attacks?
A. Apply the Trusted Subsystem pattern to protect Database A from data-driven attacks and to evaluate whether database responses contain inappropriate data. The trusted subsystem maintains a snapshot of Database A and executes the original service consumer's request message against the snapshot. The processing logic that accesses the snapshot has limited privileges in order to prevent malicious attacks from overtaking the database. If no security violation is detected during the processing of the snapshot, then the original service consumer's request is forwarded to Database A.
If an error message is generated during the processing of the snapshot, then it is returned to the original service consumer and the request is not forwarded to Database A.
Because the error message was generated on the snapshot, it cannot contain unsafe information about Database A.
B. Apply the Data Confidentiality pattern together with the Data Origin Authentication pattern. This establishes message-level security so that all messages are encrypted and digitally signed. Secondly, the Service A logic must be enhanced so that it can keep track of the trustworthiness of its service consumers If a request message originated from a trustworthy service consumer, then the request message is processed as normal. If the request message originates from a non-trustworthy service consumer, then the request message is rejected and an error message is returned to the service consumer.
C. Apply the Service Perimeter Guard pattern together with the Trusted Subsystem pattern.
This establishes a perimeter service between Database A and any service that requires access to it (including Services B and C). The perimeter service evaluates incoming data requests and filters out those that can introduce a security risk. Only request messages issued by authorized services and service consumers are forwarded to Database A.
Responses originating from Database A are further evaluated by the trusted subsystem to remove any unauthorized data. The two patterns together ensure that only authorized data is returned to the service consumer and that no request messages present a security threat to Database A.
D. Apply the Exception Shielding pattern together with the Message Screening pattern.
This establishes new logic within Service A that screens incoming request messages for data-driven attacks (such as SQL injection and XPath injection attacks), and also evaluates whether exception details returned by Database A contains potentially confidential or unsafe information. Any inappropriate exception information is replaced with sanitized content.
正解：D

質問 3：

A.
B. 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-SecurityPolicy, XML-Encryption, and XML-Signature.
C. 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
D. 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.
E. 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.
The utility 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.
正解：A,B