granting permision to a sub bucket in amazon s3 bucket. The other items remain private

bucket_policy.json

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AddPerm",
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::bucket/subbucket/*"
        }
    ]
}