MM code: Difference between revisions

Revision as of 11:44, 10 January 2008

Latest revision as of 03:14, 27 August 2024

(30 intermediate revisions by 21 users not shown)

Line 1:

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|year=1999|language=German}}</ref><ref>{{cite web|url=http://www.kartensicherheit.de/ww/de/pub/oeffentlich/sicherheitsprodukte/mm_merkmal.php|title=MM-Merkmal|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 onto the copy will be detected when trying to use the counterfeit in a German [[automated teller machine]].

The "MM Code" is a short number written physically on a credit or debit card during manufacture, hidden using [[Steganography]], adopted by the German banking industry to fight card [[Counterfeiting]]. 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 to the copy will be detected when trying to use the counterfeit in an [[Automated Teller Machine]].

==Function==

Automated Teller Machines which can read the MM code contain a special MM box which contains theand circuitrysensor to read and verify the MM code. This box sits more than an inch away from the card. It is unclear whether theThe MM codebox iswas read optically fromfor a distancelong duringtime acquisitionconsidered ofa thewell-guarded card from the slot, or if there is some kind of read head positioned closer to the card and connected to the MM Box.secret; Cashcash 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.

In order to remain effective, the MM code reliesrelied on the continued obscurity of the reading mechanism, and possibly also on the expense and difficulty of embedding a code once known. Since the arrival of the [[EMV]] chip-basebased payment protocols, the MM code has reduced significance in combatting card counterfeiting.

== Operating principle ==

== Misunderstandings about MM Code encoding ==

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 changing capacitance 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.

Public information on the MM code is somewhat limited. A variety of theories have been proposed, some of which are the result of confusion between the MM code and other proprietary anti-counterfeiting schemes.

== Related technologies ==

The first class of explanation proposes that the MM code is encoded 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.

In addition to capacitive MM code, which has been widely used in Germany since the early 1980s, a range of similar technologies have been proposed or patented, but have never been widely deployed in ATM cards:

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).

The*'''Angle first classmodulation of explanation proposes thatferromagnetic theparticles:''' MMA code is encodedembedded 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.

A third class considers encoding the code using the electrical properties of the plastic card, such as capacitance. Such an explanation requires a read head within close proximity to the card.

*'''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==

{{reflist}}

== 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|year=2003|publisher=John Wiley and Sons|isbn=0-470-85668-8|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|year=2003|publisher=Oldenbourg|isbn=3-486-25890-7|language=German}}

[[Category:Payment systems]]