Pirates on the Airwaves - Technology Information

Emedia Professional, Sept, 1999 by Linden deCarmo

New Technologies for Audio Copy Protection

The Red Book audio CD is a pirate's fantasy since it stores high-fidelity digital audio on unprotected media. Such CDs contain a "Table of Contents" that informs players where tracks (or songs) are located. The tracks themselves are composed of blocks (or sectors) of uncompressed and unprotected Pulse Code Modulation (PCM) digital audio content. CD players then read these blocks of PCM audio and transform them into analog waveforms that can be processed by your ears. Surprisingly, anyone call read these audio sectors and create bootleg content. Fortunately for the music industry, few people knew of this shocking weakness since early consumer devices were playback-only.

Once software manufacturers realized that CDs could also be used to hold data, CD-ROM drives began to proliferate. Initially, these drives used proprietary hardware interfaces and APIs, so operating system support was haphazard. Eventually, hardware manufacturers adopted standardized interfaces that enabled widespread operating system support.

Unbeknownst to most programmers, these operating systems added low-level device driver APIs to access audio data directly from Red Book CDs--a process known as Digital Audio Extraction (DAE) [See Robert A. Starrett's "Ripping Off Recordings: Digital Audio Extraction Do's, Don'ts, and Do'ers," July 99, pp. 34-46--Ed.]. Armed with these APIs, programmers could retrieve digital audio content from CDs and transport (or stream) it to a sound card. Since sound cards typically have better digital-to-analog (D/A) converters than a CD-ROM drive, audit) streaming programs offer improved sound quality. Other legitimate uses for such low-level APIs include backup and streaming multimedia APIs [See "Upgrading to DVD: Equipping PCs for DVD-ROM Playback," September 1998. pp. 62-66--Ed.].

MP3: THE KILLER APP THAT KILLED AUDIO?

Some perceptive users, however, eventually discovered that low-level APIs could be used to create perfect digital copies of audio CDs. This type of piracy was limited, however, to professional users since these APIs weren't standardized and there wasn't a so-called "killer app" to spark consumer interest. Unfortunately for the music industry, the killer app arrived in the form of MPEG-1/Layer 3 (or MP3) compression and the Internet.

Before MP3, audio content was either uncompressed or highly compressed. Uncompressed CD-quality audio isn't viable because of its bandwidth requirements (176KB/sec). By contrast, most audio compressor/decompressors (or codecs) were obsessed with bit-rates. (Bit-rates refer to the amount of audio that must be delivered per second to ensure smooth playback.) While these compression algorithms achieved significant compression ratios, most were designed to compress voice and struggled with audio fidelity.

Unlike voice-oriented codecs, MP3 uses perceptual encoding to compress audio. Perceptual encoding removes extraneous information (i.e., audio that is ignored by your ear) from the digital stream while retaining audio fidelity. Consequently, it's possible to create very low bit-rate MP3 files while minimizing the loss of audio fidelity. Furthermore, higher bit-rate MP3 files are virtually indistinguishable from the original audio files.

WHY AUDIO WANTS TO BE JUST LIKE DVD-VlDEO WHEN IT GROWS UP

In the meantime, Hollywood movie studios recognized the music industry's catastrophic mistake of releasing perfect digital copies on unprotected media and, consequently, delayed the release of the DVD-Video format for over a year until they could be assured their content was secure from casual pirates. Ultimately, the Copy Protection Technical Working Group (CPTWG) was able to reassure Hollywood about the security of DVD-Video by designing copy protection solutions like encryption, authentication, and copyright preservation.

The first phase of DVD-Video copy protection involved encryption and authentication (a.k.a., CSS). Unlike Red Book CDs, multimedia content preserved on DVD may be copy-protected at the discretion of the content owner. Consequently, DVD-ROM drives will only permit applications to retrieve sectors if they are authorized. The authorization process involves the exchange of time-based 128-bit keys between the DVD-ROM drive and appropriate DVD decoder software. Although no algorithm is hacker-proof, this particular solution is robust enough to discourage the average hacker and, therefore, satisfy the studios.

The second phase of the DVD-Video copy protection scheme revolves around content rights tracking and protection. CSS protection is simplistic: either you permit copying or you don't. However, there are circumstances where you may want your content to be copied, but you need to be able to track who is using your intellectual property and how they are using it. In addition, a pirate might break the CSS scheme, in which case you'd want to trace an illegal DVD back to its original source. The most robust solution for protecting such rights is watermarking.