970 lines
52 KiB
Plaintext
970 lines
52 KiB
Plaintext
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@BEGIN_FILE_ID.DIZHow to read the magnetic stripe from cardz
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@END_FILE_ID.DIZ
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_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
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Card-O-Rama: Magnetic Stripe Technology and Beyond
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or
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"A Day in the Life of a Flux Reversal"
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Written by
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oooOO Count Zero OOooo
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Restricted Data Transmissions
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November 99, 1999
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Look in your wallet. Chances are you own at least 3 cards that have magnetic
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stripes on the back. ATM cards, credit cards, calling cards, frequent flyer
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cards, ID cards, passcards,...cards, cards, cards! And chances are you have
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NO idea what information is on those stripes or how they are encoded. This
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detailed document will enlighten you and hopefully spark your interest in
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this fascinating field. None of this info is "illegal"...but MANY
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organizations (the government, credit card companies, security firms, etc.)
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would rather keep you in the dark. Also, many people will IMMEDIATELY
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assume that you are a CRIMINAL if you merely "mention" that you are
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"interested in how magnetic stripe cards work." Watch yourself, ok? Just
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remember that there is nothing wrong with wanting to know how things work,
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although in our present society, you may be labelled a "deviant"
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(or worse, <gasp> a "hacker")!
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Anyway, I will explain in detail how magstripes are encoded and give several
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examples of the data found on some common cards. I will also cover the
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technical theory behind magnetic encoding, and discuss magnetic encoding
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alternatives to magstripes (Wiegand, barium ferrite). Non-magnetic card
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technology (bar code, infrared, etc.) will be described. Finally, there will
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be an end discussion on security systems and the ramifications of emergent
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"smartcard" and biometric technologies.
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*DISCLAIMER*
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Use this info to EXPLORE, not to EXPLOIT. This text is presented for
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informational purposes only, and I cannot be held responsible for anything
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you do or any consequences thereof. I do not condone fraud, larceny,
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or any other criminal activities.
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*A WARNING*
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Lately, I've noticed a few "books" and "magazines" for sale that were filled
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with files on a variety of computer topics. These file were originally
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released into the Net with the intention of distributing them for free.
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However, these files are now being packaged and sold for profit. This really
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pisses me off. I am writing this to be shared for free, and I ask no
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payment. Feel free to reprint this in hardcopy format and sell it if you must
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but no profits must be made. Not a f***ing dime ,Deutschmark, Punt, Lira,
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Pound, or Centime! If anyone reprints this file and tries to sell it for a
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profit, I will hunt you down and make your life miserable.
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?????????????????????????????????????????????????????????????????????????????
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How?
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?????????????????????????????????????????????????????????????????????????????
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Use your imagination. The reality will be worse.
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** MAGSTRIPE FIELDS, HEADS, ENCODING/READING **
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Now, I'll get down to business!
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First, I am going to explain the basics behind fields, heads, encoding and
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reading. Try and absorb the theory behind encoding/reading. This will help
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you greatly if you ever decide to build your own encoder/reader from scratch
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(more on that later). Ferromagnetic materials are substances that retain
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magnetism after an external magnetizing field is removed. This principle is
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the basis of all magnetic recording and playback. Magnetic poles always occur
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in pairs within magnetized material, and magnetic flux lines emerge from the
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north pole and terminate at the south. The elemental parts of megstripes are
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ferromagnetic particles about 20 millionths of an inch long, each of which acts
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like a tiny bar magnet. These particles are rigidly held together by a resin
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binder. The magnetic particles are made by companies which make coloring
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pigments for the paint industry, and are usually called pigments. When making
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the magstripe media, the elemental magnetic particles are aligned with their
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North-South axes parallel to the magnetic stripe by means of an external
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magnetic fields while the binder hardens.
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These particles are actually permanent bar magnets with two stable polarities.
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If a magnetic particle is placed in a strong external magnetic field of the
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opposite polarity, it will reverse its own polarity (North becomes South,
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South becomes North). The external magnetic field strength required to
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produce this flip is called the coercive force, and is a measure of the
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coercivity of the particle. Magnetic pigments are available in a variety of
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coercivities (more on that later on).
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An unencoded magstripe is actually a series of North-South magnetic domains
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(see Figure 1). The adjacent N-S fluxes merge, and the entire stripe acts as a
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single bar magnet with North and South poles at its ends.
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Figure 1: N-S.N-S.N-S.N-S.N-S.N-S.N-S.N-S <-particles in stripe
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---------
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represented as-> N-----------------------------S
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However, if a S-S interface is created somewhere on the stripe, the fluxes will
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repel, and we get a concentration of flux lines around the S-S interface (same
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with N-N interface). Encoding consists of creating S-S and N-N interfaces, and
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reading consists of (you guessed it) detecting 'em. The S-S and N-N interfaces
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are called flux transitions, or flux reversals.
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||| ||| <-flux lines
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Figure 2: N------------N-N-S-S-----------------S
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--------- flux lines -> ||| |||
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The external magnetic field used to flip the polarities is produced by a
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solenoid, which can reverse its polarity by reversing the direction of current.
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An encoding head solenoid looks like a bar magnet bent into the shape of a ring
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so that the North/South poles are very close and face each other across a tiny
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gap. The field of the solenoid is concentrated across this gap, and when
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elemental magnetic particles of the magstripe are exposed to this field, they
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polarize to the opposite (unlike poles attract). Movement of the stripe past
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the solenoid gap during which the polarity of the solenoid is reversed will
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produce a single flux reversal (see Figure 3). To erase a magstripe, the
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encoding head is held at a constant polarity and the entire stripe is moved
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past it. No flux reversals, no data.
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| | <----wires leading to solenoid
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/-|-|-\<5C> |