S90-20A 全真模擬試験 DEMO

問題2: 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.
To fulfill a new security requirement, Service A needs to be able to verify that the response message sent
by Service B has not been modified during transit. Secondly, the runtime performance between Services
A and B has been unacceptably poor and therefore must be improved without losing the ability to verify
Service A's security credentials. It has been determined that the latency is being caused by redundant
security processing carried out by Service B.
Which of the following statements describes a solution that fulfills these requirements?
A. Apply the Trusted Subsystem pattern to introduce a utility service that performs the security processing
instead of Service B. The utility service can verify the security credentials of request messages from
Service A and digitally sign messages sent to Service A to enable verification of message integrity.
Furthermore, the utility service can perform the verification of security credentials submitted by Service A
only once per runtime service activity. After the first messageexchange, it can issue a SAML token to
Service A that gets stored within the current session. Service A can then use this session-based token
with subsequent message exchange. Because SAML tokens have a very small validity period (in contrast
to X.509 certificates), there is no need to perform a revocation check with every message exchange.
B. Service B needs to be redesigned so that it performs the verification of request messages from Service
A only for the first message exchange during the runtime service activity. Thereafter, it can issue a SAML
token to Service A that gets stored within the current session. Service A then uses this session-based
token with subsequent message exchanges. Because SAML tokens have a very small validity period (in
contrast to X.509 certificates), there is no need to perform a revocation check with every message
exchange.
C. WS-SecurityPolicy transport binding assertions can be used to improve performance via
transport-layer security The use of symmetric keys can keep the encryption and decryption overhead to a
minimum, which will further reduce the latency between Service A and Service B. By encrypting the
messages, attackers cannot modify message contents, so no additional actions for integrity verification
are needed.
D. The Data Origin Authentication pattern can be applied together with the Service Perimeter Guard
pattern to establish a perimeter service that can verify incoming request messages sent to Service B and
to filter response messages sent to Service A. The repository containing the verification information about
the Certificate Authorities can be replicated in the trust domain of the perimeter service. When access is
requested by Service A, the perimeter service evaluates submitted security credentials by checking them
against the locally replicated repository. Furthermore, it can encrypt messages sent to Service A by
Service B. and attach a signed hash value.
正解: A