The Algorithm Series: Digital Rights Management (DRM)

Anytime I write about digital rights management (DRM), I'm reminded that the opinions around codec or format wars are simple skirmishes compared to the strong feelings the term "DRM" evokes. On the one hand, there's the fact that many consumers despise DRM. And not just consumers who are bent on piracy. During my international travels, I can't tell you the number of complaints I've overheard from parents who download several movies for their children to watch during a long-haul flight, only to have geofencing (restrictions around geographies), 24-hour time constraints, or some other form of rights management impede their ability to pacify their children.

On the other hand, within our industry, there are groups that strongly advocate for a particular DRM scheme, such as Apple Fair­Play, Google Widevine, Microsoft PlayReady, or open source options, which are all designed to protect content licensors' rights while giving purchasers, renters, and subscribers flexible and fair options for watching content.

In this final Algorithm Series article of 2020, I'll take a step back from those strong opinions and look at the math behind two aspects of DRM: content encryption and license generation.

So if you're interested in which DRM solution is best for your particular use case, I urge you to search for "DRM" here on Streaming Media. But if you want to understand why the industry has coalesced around the math that underpins state-of-the-art encryption and license approaches, read on. I'll start with lessons learned in the early days of copy protection, then show how they inform today's modern DRM solutions.

Starting at the Beginning: VHS

There have been numerous approaches to enforcing rights management for premium content, many of which start from the premise of segmenting the world into various regions. While there was a smattering of this back before the days of consumers viewing premium content at home, with theatrical releases being delivered to movie theaters on a country-by-country basis, the concept didn't really gain traction until the advent of home video rentals and sales.

Starting with the Macrovision copy protection scheme, which would create "snowy" imagery on any VHS tape duplication, the studios began segmenting the world into regions that first accounted for over-the-air (OTA) television transmission formats—NTSC, PAL, SECAM—and then by a rough equivalent of continents, since PAL and SECAM were still in use in various former English or French colonies.

Shiny Discs

With the advent of digital video delivery on DVDs, which were sold to consumers as perfect digital copies but also had the potential to be duplicated by consumers as perfect digital copies, there was a tightening of rights management on more than just a regional basis.

As part of the premium content protection agreements that studios demanded from the consumer electronics (CE) industry, manufacturers of DVD players were required to incorporate hard-locked regions as a first line of defense in the DVD players they sold. So a DVD player sold by Sony in Europe would only play mass-produced DVDs that were designated for the same region. Any attempt to play DVDs sold in Europe in a DVD player sold in North America would result in a region error being displayed on the screen of the North American DVD player.

In some ways, it wasn't a hard sell for CE manufacturers to meet the studios' demands, since many of the media and entertainment conglomerates owned both studios and CE device manufacturers. But it turned out that the studios and industry representatives at the Motion Picture Association of America (MPAA) weren't satisfied with just using regional locks on DVD players or on the discs themselves. That desire for additional security led to what was arguably the world's first DRM solution: the Content Scramble System (CSS).

CSS was included in each DVD player as a joint rights-managemen...