S90-20A 全真模擬試験 DEMO

問題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.
Component B is considered a mission critical program that requires guaranteed access to and fast
response from Database A. Service A was recently the victim of a denial of service attack, which resulted
in Database A becoming unavailable for extended periods of time (which further compromised
Component B). Additionally, Services B, C, and D have repeatedly been victims of malicious intermediary
attacks, which have further destabilized the performance of Service A.
How can this architecture be improved to prevent these attacks?
A. A utility service is created to encapsulate Database A and to assume responsibility for authenticating all
access to the database by Service A and any other service consumers. Due to the mission critical
requirements of Component B, the utility service further contains logic that strictly limits the amount of
concurrent requests made to Database A from outside the organizational boundary. The Data
Confidentiality and Data Origin Authentication patterns are applied to all message exchanged within the
external service composition in order to establish message-layer security.
B. Service Consumer A generates a private/public key pair and sends this public key and identity
information to Service A. Service A generates its own private/public key pair and sends it back to Service
Consumer A. Service Consumer A uses the public key of Service A to encrypt a randomly generated
session key and then sign the encrypted session key with the private key. The encrypted, signed session
key is sent to Service A. Now, this session key can be used for secure message-layer communication
between Service Consumer A and Service A. The Service Perimeter Guard pattern is applied to establish
a perimeter service that encapsulates Database A in order to authenticate all external access requests.
C. Services B, C, and D randomly generate Session Key K, and use this key to encrypt request and
response messages with symmetric encryption. Session Key K is further encrypted itself asymmetrically.
When each service acts as a service consumer by invoking another service, it decrypts the encrypted
Session Key K and the invoked service uses the key to decrypt the encrypted response. Database A is
replicated so that only the replicated version of the database can be accessed by Service A and other
external service consumers.
D. The Direct Authentication pattern is applied so that when Service Consumer A submits security
credentials, Service A will be able to evaluate the credentials in order to authenticate the request
message. If the request message is permitted, Service A invokes the other services and accesses
Database A. Database A is replicated so that only the replicated version of the database can be accessed
by Service A and other external service consumers.
正解: A