The VISA PIN verification algorithm performs a multiple encipherment of a value, called the transformed security parameter (TSP), and a extraction of a 4-digit PIN verification value (PVV) from the ciphertext. The calculated PVV is compared with the referenced PVV and stored on the plastic card or data base. If they match, verification is successful.

PVV Generation Algorithm

The algorithm generates a 4-digit PIN verification value (PVV) based on the transformed security parameter (TSP).

The algorithm requires the following input parameters:

• A 64-bit TSP
• A 128-bit PVV generation key

1. A multiple encipherment of the TSP using the double-length PVV generation key is performed.
2. The ciphertext is scanned from left to right. Decimal digits are selected during the scan until four decimal digits are found. Each selected digit is placed from left to right according to the order of selection. If four decimal digits are found, those digits are the PVV.
3. If, at the end of the first scan, less than four decimal digits have been selected, a second scan is performed from left to right. During the second scan, all decimal digits are skipped and only nondecimal digits can be processed. Nondecimal digits are converted to decimal digits by subtracting 10. The process proceeds until four digits of PVV are found.

Figure 19 illustrates the PVV generation algorithm.

Figure 19. PVV Generation Algorithm

PVV Verification Algorithm

The algorithm requires the following input parameters:

• A 64-bit TSP
• A 16-bit referenced PVV
• A 128-bit PVV verification key

A PVV is generated using the PVV generation algorithm, except a PVV verification key rather than a PVV generation key is used. The generated PVV is compared with the referenced PVV. If they match, verification is successful.

Interbank PIN Generation Algorithm

The Interbank PIN calculation method consists of the following steps:

1. Let X denote the transaction_security parameter element converted to an array of 16 4-bit numeric values. This parameter consists of (in the following sequence) the 11 rightmost digits of the customer PAN (excluding the check digit), a constant of 6, a 1-digit key indicator, and a 3-digit validation field.
2. Encrypt X with the double-length PINGEN (or PINVER) key to get 16 hexadecimal digits (64 bits).
3. Perform decimalization on the result of the previous step by scanning the 16 hexadecimal digits from left to right, skipping any digit greater than X'9' until 4 decimal digits (for example, digits that have values from X'0' to X'9') are found.

   If all digits are scanned but 4 decimal digits are not found, repeat the scanning process, skipping all digits that are X'9' or less and selecting the digits that are greater than X'9'. Subtract 10 (X'A') from each digit selected in this scan.

   If the 4 digits that were found are all zeros, replace the 4 digits with 0100.

4. Concatenate and use the resulting digits for the Interbank PIN. The 4-digit PIN consists of the decimal digits in the sequence in which they are found.