Users are uploaded encrypted files to different locations in an S3 bucket. You then ensure the files are transferred to a central S3 location. How can you ensure the contents are the same for the object after the files have been transferred to the central S3 bucket?

Answer options:

A.Use the E Tags associated with the objects
B.Use the CompareObjects API command
C.Compare the size of the objects
D.Use the object key for comparison

Answer – A
You can actually compare the ETag to ensure that the MD5 digest of the object data is the same.
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ETag
The entity tag is a hash of the object. The ETag reflects changes only to the contents of an object, not its metadata. The ETag may or may not be an MD5 digest of the object data. Whether or not it is depends on how the object was created and how it is encrypted as described below:
Objects created by the PUT Object, POST Object, or Copy operation, or through the AWS Management Console, and are encrypted by SSE-S3 or plaintext, have ETags that are an MD5 digest of their object data.
Objects created by the PUT Object, POST Object, or Copy operation, or through the AWS Management Console, and are encrypted by SSE-C or SSE-KMS, have ETags that are not an MD5 digest of their object data.
If an object is created by either the Multipart Upload or Part Copy operation, the ETag is not an MD5 digest, regardless of the method of encryption.
Type: String
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Option B is incorrect since the API command is not applicable or present for S3
Options C and D are incorrect since the size and key name cannot be solely used to ensure the contents have not been tampered with
For more information on REST response headers, please refer to the below URL
https://docs.aws.amazon.com/AmazonS3/latest/API/RESTCommonResponseHeaders.html