Which of the following steps will implement these requirements?

Explanations:

Creating a new S3 bucket in a separate AWS account for centralized storage of CloudTrail logs is essential for fulfilling the requirement of having a distinct account for centralized services. Enabling “Log File Validation” ensures integrity by allowing verification of the logs, detecting any modifications made to them.

Using an existing S3 bucket in one of the accounts does not satisfy the requirement of creating a separate account for centralized storage. While it is important to apply the correct bucket policy to allow CloudTrail access, this option fails to meet the requirement for a new account and centralized S3 bucket.

Applying a bucket policy to the new centralized S3 bucket that permits the CloudTrail service to perform “s3” and “s3” actions is necessary to allow CloudTrail to log API calls into the bucket. Specifying the appropriate resource ARNs for the trails ensures that the policies are applied correctly to the right resources.

Using unique log file prefixes for trails in each AWS account is crucial for differentiating the logs from different accounts. This organization helps in easily identifying and managing the logs for each account when they are stored in the centralized S3 bucket.

Configuring CloudTrail in the centralized account does not align with the requirement of having CloudTrail configured in each of the five AWS accounts. Each account must individually log to the centralized S3 bucket, rather than centralizing the configuration in a single account.

While enabling encryption using AWS Key Management Service is a good practice for securing log files, it is not explicitly mentioned as a requirement in the scenario provided. Therefore, it is not essential to implement the main requirements of logging and detecting modifications to the logs.