This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
There are several approaches. An article with a good overview
of some popular protection technologies can be found at
Another source is the "CD Protections" articles on
For anyone interested in protecting their own discs: don't bother. Copy
protection, on the whole, does not work. If you have a major application,
such as a game or CAD package, you may want to consider one of the
commercially licensed schemes listed later, or (heaven forbid) the use of a
dongle. In general, though, if the disc can be read, then the contents
can be copied. If you don't want somebody to make a copy of your stuff,
then you'd better encrypt it (3-19).
A simple and commonly seen technique is to increase the length of several
files on the CD so that they appear to be hundreds of megabytes long.
This is accomplished by setting the file length in the disc image to be
much larger than it really is. The file actually overlaps with many
other files. So long as the application knows the true file length,
the software will work fine. If the user tries to copy the files onto
their hard drive, or do a file-by-file disc copy, the attempt will fail
because the CD will appear to hold a few GB of data. (In practice this
doesn't foil pirates, because they always do image copies. And, no, none
of the standard software provides a way to create such discs.)
One possible implementation, given sufficient control over the reader and
mastering software, is to write faulty data into the ECC portion of a data
sector. Standard CD-ROM hardware will automatically correct the "errors",
writing a different set of data onto the target disc. The reader then
loads the entire sector as raw data, without doing error correction. If it
can't find the original uncorrected data, it knows that it's reading a
"corrected" duplicate. This is really only viable on systems like game
consoles, where the drive mechanism and firmware are well defined. This
can be defeated by doing "raw" reads.
A more sophisticated approach is to write special patterns of data to the
disc. The stream of data that results, after EFM encoding, is difficult
for some recorders to reproduce successfully, apparently because they don't
choose correct values for the merging bits. This is often referred to on
web sites as "writing regular EFM patterns" or "weak sectors". See section
(2-43) for details on EFM.
A less sophisticated -- and no longer effective -- method is to press a silver
CD with data out beyond where a 74-minute CD can write. Copying the disc
used to require hard-to-find CD-R blanks, but now it's easy to use an
overburned 80-minute disc (sections (3-8-1) and (3-8-3)).
The approach some PC software houses have taken is to use nonstandard
gaps between audio tracks and leave index marks in unexpected places.
These discs are uncopyable by most software, and it may be impossible
to duplicate them on drives that don't support disc-at-once recording
(see section (2-9)). With the right reader and software, though, this
isn't much of a problem either.
A method that enjoyed some popularity was non-standard discs with a track
shorter than 4 seconds. Most recording software, and in fact some recorders,
will either refuse to copy a disc with such a track, or will attempt to
do so and fail. A protected application would check for the presence and
size of the track in question. Some recorders may succeed, however, so
this isn't foolproof. (In one case, a recorder could write tracks that
were slightly over three seconds, but refused to write tracks that were
only one second. There may be a limit below which no recorder will write.)
In such cases, the pirates need to remove the explicit check from the
Putting multiple data tracks interleaved with audio tracks on a CD will
confuse some disc copiers. However, it's difficult to actually use the
data on those additional tracks.
Sometimes the copy of a disc will have a different volume label. This
usually only happens with file-by-file copies, not disc image copies, so
checking the disc name is marginally useful but not very effective.
Modifying the TOC so that the disc appears to be larger than it really is
will convince some copy programs that the source disc is too large.
Some of the fancier technologies use non-standard pit geometry that cause
players to read the data differently on consecutive attempts. Sometimes
the player sees a "1", sometimes a "0". If, when reading the track, the
CD-ROM drive sees different data each time, the software knows that the
disc is an original. A duplicate disc will return the same data reliably.
(So too will some CD-ROM drives... this technology is not without problems.)
Some programs will examine the disc to try to determine if it's a CD-R.
This doesn't work on all readers, and it's possible to disguise discs,
so this isn't very effective.
CloneCD (section (6-1-49)) can copy many copy protected discs without
trouble, given the right combination of reader and writer. Its main
feature is "raw" reads and writes, which not all drives support.
The Laserlok system from http://www.diskxpress.com/ claims to be able to
prevent unauthorized disc duplication at a low cost. It can be copied
An unrelated product called LaserLock, from MLS LaserLock International
(http://www.laserlock.com/) has similar features. It can be copied by
TTR Technology's DiscGuard (http://www.ttr.co.il/ or http://www.ttrtech.com/
claims to be able to write a signature onto pressed CDs and CD-Rs that is
detectable by all CD-ROM drives but isn't reproducible without special
hardware. A program could use this for copy protection by checking for
the presence of the signature, and refusing to run if it's not there.
Sony DADC is promoting a similar product called Securom. Some information
is at http://www.sonydadc.com/hotnews/secu_fra.htm.
Yet another variant is C-Dilla's SafeDisc. They were bought by Macrovision
(http://www.macrovision.com/). Their more recent product, SafeDisc 2,
was the first to feature "weak sectors".
Yet another variant is CD-Cops from Link Data Security