MM code: Difference between revisions

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An '''MM code''' (the "MM" being an abbreviation for the [[German language|German]] "Moduliertes Merkmal") is a "machine-readable modulated" feature that has been added to German [[debit card]]s during manufacture as an anti-[[counterfeiting]] measure since 1979.<ref>{{cite book|author=Wolfgang Rankl and Wolfgang Effing|title=Handbuch der Chipkarten. 3rd edition|publisher=Hanser Verlag|dateyear=1999|language=German}}</ref><ref>{{cite web|url=httpshttp://www.kartensicherheit.de/ww/de/pub/praeventionoeffentlich/sicherheitsprodukte/mm_merkmal.php|title=MM-Merkmal|work=|author=|publisher=|date=|accessdate=2008-01-10|language=German|archive-url=https://web.archive.org/web/20090522165336/http://www.kartensicherheit.de/ww/de/pub/oeffentlich/sicherheitsprodukte/mm_merkmal.php|archive-date=2009-05-22|url-status=dead}}</ref> It was developed by "Gesellschaft für Automation und Organisation" (a subsidiary of Giesecke & Devrient) in Munich for the German ec-Card system and MM verification devices have been added to German ATMs from 1982 onwards.<ref name="ct1996">{{cite news|author=Carsten Meyer|url=http://www.heise.de/ct/96/07/094/|title=Nur Peanuts &mdash; Der Risikofaktor Magnetkarte|work=[[c't]]|date=July 1996|pages=94|language=German|publisher=Heise Zeitschriften Verlag}}</ref> If a payment card contains an MM code as well as a magnetic stripe, any fraudster who counterfeits the card but fails to read and duplicate the MM code on toonto the copy will be detected when trying to use the counterfeit in ana German [[Automatedautomated Tellerteller Machinemachine]].

==Function==

[[Image:Mmcode.png|thumbnail|Diagram showing verification of the MM Code.]]

Automated Teller Machines which can read the MM code contain a special MM box and sensor to read and verify the MM code. The MM box was for a long time considered a well-guarded secret; cash machine manufacturers do not access or service the box. The MM code consists of two components, one stored on the magnetic stripe, and one hidden inside the card's material. During MM code verification, a cryptographic operation is performed to check that the MM code on the magnetic stripe corresponds to the hidden one. The presence of the keyed cryptographic operation means that the correct MM code for a counterfeit cannot be calculated from the magnetic stripe information alone without knowledge of the key – it must be read from the original card itself.

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== Operating principle ==

The MM feature is encoded in the middle layer of an [[ISO/IEC 7810]] card as a [[bar code]] formed by two materials with different electrical properties.<ref name="ct1996"/> A capacitive sensor head near the magstripe reader observes the alternatingchanging capacitycapacitance as the card is moved past the sensor and decodes the represented number. This sensor works in a similar fashion to the magnetic read head found in a magstripe card reader, except that it senses not a change in [[magnetic flux]], but a change in the [[dielectric constant]] of the card's material. It reads a second data stripe that, unlike the magstripe, cannot easily be rewritten with off-the-shelf equipment.

== Related technologies ==

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*'''Angle modulation of ferromagnetic particles:''' A code is embedded into the magnetic stripe using read and write heads operating diagonally to the direction of swipe in the reader. With appropriate signal processing, these can read and encode a small amount of additional data which is polarised in a different axis to the ISO standard tracks.

*'''Infrared barcodes:''' The second class concerns encoding the code onto the plastic base of the card using special inks (probably a bar code), or reading a code which is inherently embedded as part of the plastic manufacturing process for each batch. Such a code may only be visible under infrared illumination (or other invisible wavelength).

* [[ Wiegand effect #Wiegand keycards | Wiegand keycards]], like capacitive MM codes, embed a code into the middle layer of the card, and so are more durable and difficult to counterfeit than printed barcodes or magnetic stripes on the surface of the card.<ref>

[https://books.google.com/books?id=Ehc1omWy6iMC "Security Supervision and Management: The Theory and Practice of Asset Protection"].

2007.

p. 365.

</ref>

==References==

{{refsreflist}}

== Further reading ==

* {{cite book|title=Smart Card Handbook|url=https://archive.org/details/smartcardhandboo00rank_578|url-access=limited|author=W Rankl and W Effing|pages=[https://archive.org/details/smartcardhandboo00rank_578/page/n70 36]&ndash;38|dateyear=2003|publisher=John Wiley and Sons|isbn=04708566880-470-85668-8|doi=10.1002/047085670X.ch3}}

* {{cite book|title=E-Finance: Elektronische Dienstleistungen in der Finanzwirtschaft|author=Freimut Bodendorf and Susanne Robra-Bissantz|pages=49&ndash;50|dateyear=2003|publisher=Oldenbourg|isbn=34862589073-486-25890-7|language=German}}

[[Category:Payment systems]]