Editing Personal identification number (section)

==== IBM 3624 method====
One of the earliest ATM models was the [[IBM 3624]], which used the IBM method to generate what is termed a ''natural PIN''.  The natural PIN is generated by encrypting the primary account number (PAN), using an encryption key generated specifically for the purpose.<ref>{{cite web
  | url=http://publib.boulder.ibm.com/infocenter/zos/v1r9/index.jsp?topic=/com.ibm.zos.r9.csfb400/csfb4z80539.htm
  | title=3624 PIN Generation Algorithm
  | publisher=IBM
  }}</ref> This key is sometimes referred to as the PIN generation key (PGK).  This PIN is directly related to the primary account number.  To validate the PIN, the issuing bank regenerates the PIN using the above method, and compares this with the entered PIN.

Natural PINs cannot be user selectable because they are derived from the PAN.  If the card is reissued with a new PAN, a new PIN must be generated.

Natural PINs allow banks to issue PIN reminder letters as the PIN can be generated.