                         The ISO9660 File System
                 Sleuth Kit Implementation Notes (SKINs)
                        http://www.sleuthkit.org

                            Wyatt Banks, Crucial Security
                        Last Updated: June 2005



INTRODUCTION
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The ISO9660 file system is used on many platforms and has many
variations and extensions.  At the most basic level of ISO9660 there
are several differences than traditional filesystems due to the type
of media available.

This document gives a quick overview of ISO9660 and how it was 
implemented.

The Sleuth Kit allows one to investigate an ISO9660 image in the same
ways as any UNIX image, including:

  - Creation of ASCII timeline of file activity
  - File and directory level analysis


ISO9660 OVERVIEW
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This provides a quick introduction to the ISO9660 file system.  The
terms used are different then with other file systems.  For a full
overview of the file system, refer to the document "Volume and File
Structure of CDROM for Information Interchange"

http://www.ecma-international.org/publications/standards/Ecma-119.htm


Volume descriptors
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ISO9660 uses structures called Volume Descriptors to store information
about the directory hierarchy of an ISO9660 volume.  At 32768 bytes
into the image there is a contiguous list of volume descriptors.
A primary volume descriptor contains an address of a Path Table which
is a list of every directory on the volume.  In this path table each
directory record has a single run of contiguous bytes known as an
Extent.  Each directory's single data extent contains a group of
contiguous directory descriptors which represent files, directories
or other standard file types.

Primary volume descriptors only allow uppercase filenames in the
8.3 format (8 chars dot 3 chars).

Supplementary volume descriptors are very similar to primary volume
descriptors.  The main difference is that supplementary volume
descriptors store filenames as UCS-2 characters and are used
in Microsoft Joliet extensions to allow mixed case filenames up to
103 characters.

All volume descriptors are stored at least once, with there being a
requirement to have only a single primary volume descriptor for an
image to be valid.  Supplementary volume descriptors usually contain
the same data as primary volume descriptors.

FILES
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ISO9660 file are stored in an extent whose size is measured in bytes.

A file is considered unique if its extent address is unique.

DIRECTORIES
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Directory names are only stored in the path table of the volume
descriptor.  As a directory is encountered as a directory descriptor
inside another directory's extent, the address of its data extent
is examined by the ISO9660 implementation to see if we've seen this
directory before and figure out what its name is.

Directories are unusual in the way they are identified as a unique
inode.  If we examine the root directory using a primary volume
descriptor then its extent address is where on the volume the extent
containing the list of directory descriptors with 8.3 encoded names
exists.  If we examine the root directory of that same volume using 
a supplementary volume descriptor we will find that the extent
address is different because these directory descriptors are UCS-2
encoded, even though each directory descriptor will point at the same
data extent for each file.

This last paragraph is quite complicated.  Lets simplify:

Imagine a CD with 3 files on it: file-1.txt, file-2.txt, file3.txt.

The path table in a primary volume descriptor has one directory in it
and its extent contains 3 directory descriptor structures with 8.3 
uppercase encoding.  The path table in a supplementary volume
descriptor describing this same volume has one directory but its extent
is different because those 3 directory descriptor structures are
different than the previous 3.  The files are not considered unique
because their extent addresses (where their data lies) is not unique.

OF NOTE:
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Due to many reports of mastering software errata, there are some
issues that The Sleuth Kit handles that the specifications for ISO9660
say will never happen.  The specs say that there is only one unique
primary volume descriptor per volume.  The Sleuth Kit handles the 
possibility of finding more and alerts the user to this.

Inodes don't really exist in ISO9660 so the implementation is 
improvised based on anything thats extent is unique is a different
file.  The pseudo inode strucutre is stored in a linked list to make
viewing an entire image faster.

ISO9660 stores many fields as both byte order.  A 32 bit number
will take 8 bytes, the first 4 are little endian, the last 4 are
big endian.

USING THE SLEUTH KIT WITH ISO9660
=======================================================================
The Sleuth Kit allows one to view all aspects of the ISO9660 structure.

All Sleuth Kit commands should work the same as their counterparts.

Note that Autopsy can automate this process for you and allows you
to view all attributes.

   http://www.sleuthkit.org/autopsy

WHAT THE SLEUTH KIT CANNOT CURRENTLY DO
=======================================================================
There are a few things that The Sleuth Kit is not yet able to do
with ISO9660:

- Multisessions CDs are not handled.
- High Sierra is not handled.
- Files that are stored with an interleave gap

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CVS Date: $Date: 2007/12/19 14:42:20 $
