Editing Personal identification number (section)

==== IBM 3624 + offset method====
To allow user-selectable PINs it is possible to store a PIN offset value.  The offset is found by subtracting the natural PIN from the customer selected PIN using [[modular arithmetic|modulo]] 10.<ref>{{cite web
  | url=http://publib.boulder.ibm.com/infocenter/zos/v1r9/index.jsp?topic=/com.ibm.zos.r9.csfb400/csfb4z80541.htm
  | title=PIN Offset Generation Algorithm
  | publisher=IBM}}</ref> For example, if the natural PIN is 1234, and the user wishes to have a PIN of 2345, the offset is 1111.

The offset can be stored either on the card track data,<ref>{{cite web
    | url=http://www.gae.ucm.es/~padilla/extrawork/tracks.html
    | title=Track format of magnetic stripe cards
    | publisher=Gae.ucm.es
    | access-date=2010-04-25
    | archive-date=2014-09-28
    | archive-url=https://web.archive.org/web/20140928190852/http://www.gae.ucm.es/~padilla/extrawork/tracks.html
    | url-status=dead
    }}</ref> or in a database at the card issuer.

To validate the PIN, the issuing bank calculates the natural PIN as in the above method, then adds the offset and compares this value to the entered PIN.