devot:eeDevoted to ExpressionEngine

We’re considering using Protected Links for a client’s site, but I’d like some more information on the method used to protect the links.

Is it just using an ?ACT= EE URL with a hash to obfuscate the URL, which ultimately resolves to the actual URL?  Or is it actually curl’ing the data from the requested URL, and passing it through to the client browser via PHP?

The reason I ask if we’ve evaluated another product that does similar things, but it just does the former, so savvy people can inspect the network stream in their web browser, and gain access to the original, non-obfuscated URL.

The second. It is streaming the file contents using Curl (or directly from file system, or using Amazon S3 API). The actual file URL is never exposed (not even speaking about that with this module you can serve the files that are placed above your site root directory)

Great!  One last question… does it work with ranged downloads to allow it to be used for streaming media?

It depends on the player used. Some players require that you actually provide file name with an extension (e.g. mp4). Other thank this, the add-ons can set the content-type header and so you can use it to stream media.

So we purchased the product… due to the nature of the site, there’s no way we can generate a link for every file that needs protecting, so instead we’re going to be doing it dynamically.

The main thing that is missing functionality-wise is the ability to limit the total number of downloads per member over a specified time period.

For instance, we’d like to allow 20 downloads per month for people who are of a given member group.  We don’t care how many times they download an individual thing, but we care that they can only download a max of 20 unique pieces of content per month.

Yes, you’ll need some other way around this.
What you could do, for example, is to introduce an “intermediate” page that user will be send to prior to showing the link and restrict access to that page.
However I don’t know whether any existing EE add-on has the capability that you need or you’ll need to build it yourself.