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Excerpt from Wikipedia regarding the calculation of CDDB disc ids:

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CDDB1 identifies CDs with a 32-bit number, usually displayed as a hexadecimal
number containing 8 digits: XXYYYYZZ. The first two digits (labeled XX)
represent a checksum based on the starting times of each track on the CD. The
next four digits (YYYY) represent the total time of the CD in seconds from the
start of the first track to the end of the last track. The last two digits
(ZZ) represent the number of tracks on the CD.

For example, suppose a CD contains one track. Then the ZZ digits in the disc
ID will be "01".

Now suppose that the total duration of the CD is 3610 seconds (from the start
of track 1 to the end of track 1 in this case). This number is decimal, and
must be converted into the hexadecimal equivalent "0e1a" which form the YYYY
portion of the disc ID.

Finally, the two-digit checksum needs to be calculated from the start time in
seconds of each track. There is one track in this example CD, and as with most
CDs, the first track starts at 2 seconds (there is a 2 second silence leader).
Therefore, summing up all of the decimal digits of each track start time
yields the value 2. This value is less than 255, so it does not need to be
evaluated modulo 255; and therefore, the XX digits of the disc ID are "02".
According to freedb.org, the example code is done modulo 255 and not 256.

So the full disc ID of the example CD is "020e1a01". Any CD which contains one
track with a duration of 3610 seconds starting 2 seconds from the beginning of
the CD will have this disc ID. To distinguish between different CDs which
happen to have the same disc ID, the CDDB1 database is organized into multiple
categories. If there is a conflict with different CD releases possessing the
same CDDB1 id, they can be placed in a different category (such as classical,
rock, blues, folk or misc).

Sample code for calculating CDDB1 disc IDs in various programming languages is
available on the web, such as in Java.


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Licensing issues

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The original software behind CDDB was released under the GNU General Public
License, and many people submitted CD information thinking the service would
also remain free. The license was later changed, however, and some programmers
complained that the new license included certain terms that they couldn't
accept: if one wanted to access CDDB, one was not allowed to access any other
CDDB-like database (such as freedb), and any programs using a CDDB lookup had
to display a CDDB logo while performing the lookup.

In March 2001, CDDB, now owned by Gracenote, banned all unlicensed
applications from accessing their database. New licenses for CDDB1 (the
original version of CDDB) were no longer available, since Gracenote wanted to
force programmers to switch to CDDB2 (a new version incompatible with CDDB1
and hence with freedb).

The license change motivated the freedb project, which is intended to remain
free.

freedb is used primarily by media players, cataloguers, audio taggers and CD
ripper software. As of version 6 of the freedb protocol, freedb accepts and
returns UTF-8 data.