PIN Offset Generation algorithm

To allow the customer to select his own PIN, a PIN offset is used by the IBM 3624 PIN generation algorithm to relate the customer-selected PIN to the generated PIN.

The PIN offset generation algorithm requires two parameters in addition to those used in the 3624 PIN generation algorithm. They are a customer-selected PIN and a 4-bit PIN check length. The length of the customer-selected PIN is equal to the assigned-PIN length, n.

The 3624 PIN generation algorithm described in the previous section is performed. The offset data value is the result of subtracting (modulo 10) the leftmost n digits of the intermediate PIN from the customer-selected PIN. The modulo 10 subtraction ignores borrows. The rightmost m digits of the offset data form the PIN offset, where m is specified by the PIN check length. Note that n cannot be less than m.

Figure 1 illustrates the PIN offset generation algorithm.