Showing thumbnail and download link of attachment attribute on plugin

Summary:

Is it possible to generate or retrieve thumbnail URL and allow download of the attachment URL (image/PDF) on the plugin page without downloading file using individual REST API?

We have a plugin that shows the list of activities. The activities have an attribute of type attachment and customer wants to display thumbnail or link of the attachment to it can be reviewed on the plugin page.

The activity details page shows thumbnail and URL to the attachment in below format. Is it possible to use the same format on the plugin page?

If yes, how do we generate URL and compute the signature included on the URL. If there is any relevant document, that would be a great help.