libmsr/README.file-specification at master · ioerror/libmsr · GitHub

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This document introduces the MagPack file format specification. Currently
there is no open or free standard for encoding the data and relevant metadata of
magnetic retrieval procedures. MagPack aims to fill that void. MagPacks are
important for the capture, analysis, and archival of information pertaining
to magnetic information.

The MagPack file format details important information for data and meta-data
relating to the capture of magnetic fields. This document outlines the
abstract physical phenomenon of magnetic stripes, the concrete methods used to
capture analog or digital data, and finally the format of the data as it is
stored on a computer system.

Magnetic fields are generally a series of semi-independent waveforms encoded
perpendicularly across a horizontal plane of ferromagnetic material.

The horizontal plane is often referenced in literature as a stripe, a
ferromagnetic tape, or as a magnetic section of a card shaped object. The field
strength of the magnetic waveforms is measured in Oersted units. Generally
these units are grouped into high and low Oersteds; It is common to see low-co
or hi-co as representations of low and high Oersted coercivity respectively.

It is possible to measure the Oersted rating of a given magnetic field with a
B-H Analyzer. The B-H Analyzer measures residual flux density (Br) and coercive
force (Hc). In practice such an analyzer is unnecessary excepting specific
cases with serious forensic requirements. Ferromagnetic material that allows
for low coercivity state changes appear lighter in color. It is common to see
higher coercivity magnetic material approaching a darker black color.

There are a variable number of magnetic waveforms on a given horizontal plane.
A plane may have one large waveform encoded across the ferromagnetic material
or many smaller waveforms. Any given waveform may have encoding breaks across
the horizontal plane. It is uncommon to see such breaks but it is not
technically impossible, it is merely uncommon.

A magnetic waveform in this context is commonly referred to as a track of data.
There are magnetic variations in each track. In addition to the coercive force
of a given waveform, the track's waveform may not be perpendicular to the
longitude of the magnetic material. It may be written at an arbitrary and
consistent angle. This may be the result of magnetic write head mis-alignment
or because of a deliberate alignment that is consistent across an entire
system. Often angles are used to prevent simple copying techniques, reads from
cheaper ISO 7811 capable readers, or to prevent accidental demagnetization. The
physical width of each waveform, the length of the waveform, the height of the
waveform varies. Each of these elements is a unique characteristic that may be
used to identify different magnetic writing elements.

Each waveform represents either analog or digitally encoded data. Commonly used
cards are encoded as specified in ISO 7811. Many magnetic devices have ISO 7811
specific hardware for encoding and decoding. Such hardware is insufficient for
reading any custom formatted field information. To better understand custom
formats, it's important to have multiple avenues for inspection.

The two best known methods of sensing a magnetic field are, most commonly,
electronic sensing of a magnetic waveform, and secondly, with non-electronic
ferro-fluids in the form of a spray or in a plastic dish.

Electronic sensing of a waveform is stunningly simple in principle. Energy is
transferred by the movement of a magnetic medium with an arbitrary encoded
waveform across a magnetic sensing head. The magnetic field is converted into
electrical energy as a result of kinetic energy. The electronic signals have a
fluctuation that is directly correlated to the fluctuation of the magnetic
field. Flux changes are called zones. The series of electronic bursts is an
analog electrical signal that is commonly amplified and finally interpreted.
Interpretation of the analog signal relates to the distance between zones and
the content of the zones. The flux changes generally must be sensed at a
constant rate. This data is usually processed with an analog to digital signal
processor in order to understand the electronic bursts in context. It is
possible to use a sound card or custom circuitry. Electronic reading of
magnetic fields is of variable quality.

Non-electronic ferro-fluids are even simpler. Ferro-fluids are often a brown or
blackish color; It is common to see ferro-fluids spray cans and reusable dishes
filled with ferro-fluids. It is possible to visually see the waveform of the
field when a ferro-fluid is sprayed, coated or set on a magnetic substance. It
is often possible to visually see a continuous line with a ferrorfluid viewer
if the magnetic writing element lacks proper shielding at the top and bottom of
the waveform. It is possible to process an optical form of the magnetic field
to confirm an electronic read. High resolution scans with high resolution
ferro-fluids allow for extremely high quality interpretation of magnetic field
fluctuations.

To properly capture information about a specific magnetic field, a high
resolution scan of a fluid coated field and of properly aligned electronic read
is necessary.

It it proposed that the following data should be captured about a given
magnetic substance:

    Date and time of sample capture
    Suspected date and time of sample creation
    Measured or suspected Hc rating (common cards have common Oersted ratings)
    Device name, model, or method used for the capture of the specimen
    Angle of field waveforms relative to the longitude of the substance

Visual field sampling:

    Fluid coating and high resolution (1400 DPI) scan of the coated field
    The scan must be in PNG or BMP format

ISO 7811 electronic sampling:

    Track numbers
    Bit width per track
    Bits per inch per track
    Likely overall speed of swipe if available
    The contents should be represented as a byte array for each track

Raw or unformatted electronic bit pattern sampling:

    Angle of write
    relative to length of track
    Track numbers Bit width per track
    Bits per inch per track
    Likely overall speed of swipe if available
    The contents should be represented as a byte array for each track

Electronic audio sampling:

    Encoding format (eg: AFMT_S16_LE )
    Number of channels (eg: mono or stereo)
    Sample rate (eg: 192000)
    Total sample time (eg: milliseconds)

It is important to capture as many sample types as is possible. It is possible
to positively confirm data given a large set of sampling techniques. It makes
testing and transformation between different devices with different
capabilities simple.

The format of the data packing is currently unspecified. This draft will be
updated when I have slept.