MM code: Difference between revisions

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The '''MM code''' 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>Wolfgang Rankl, Wolfgang Effing: Handbuch der Chipkarten. 3rd edition Hanser Verlag, 1999.</ref><ref>[https://www.kartensicherheit.de/ww/de/pub/praevention/sicherheitsprodukte/mm_merkmal.php MM-Merkmal]</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">Carsten Meyer: [http://www.heise.de/ct/96/07/094/ Nur Peanuts – Der Risikofaktor Magnetkarte]. [[c't]] 7/1996, p. 94</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 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 the circuitry to read the MM code. This box sits more than an inch away from the card. It is unclear whether the MM code is read optically from a distance during acquisition of the card from the slot, or if there is some kind of read head positioned closer to the card and connected to the MM Box. 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. 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.

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 relied on the obscurity of the reading mechanism and the expense and difficulty of embedding a code once known. Since the arrival of the [[EMV]] chip-base payment protocols, the MM code has reduced significance in combatting card counterfeiting.