WPS PIN Code的規則

1. WPS PIN Code checksum運算
For 8-digit numeric PINs, the last digit in the PIN is used as a checksum of the other digits. 

Ex:
The 7-digit numeric PINs is "1234567".
The 8th digit should be "0".

 ( 1*3 + 2*1 + 3*3 + 4*1 + 5*3 + 6*1 + 7*3 ) = 60
 60 % 10 = 0
 10 - 0 = 10
 10 % 10 = 0
 Get the 8th digit is "0".
 So the 8-digit numberic PINs is "12345670".
 
If the 7-digit numberic PINs is "5967201", 
the 8th digit should be "2".
 ( 5*3 + 9*1 + 6*3 + 7*1 + 2*3 + 0*1 + 1*3) = 58
 58 % 10 = 8
 10 - 8 = 2
 2 % 10 = 2
 Get the 8th digit is "2".
 So the 8-digit numberic PINs is "59672012".

The corresponding algorithm to compute the checksum digit given the other seven random PIN digits is:

/**
 * wps_pin_checksum - Compute PIN checksum
 * @pin: Seven digit PIN (i.e., eight digit PIN without the checksum digit)
 * Returns: Checksum digit
 */
unsigned int wps_pin_checksum(unsigned int pin)
{
 unsigned int accum = 0;
 while (pin) {
  accum += 3 * (pin % 10);
  pin /= 10;
  accum += pin % 10;
  pin /= 10;
 }

 return (10 - accum % 10) % 10;
}

2. 驗證WPS PIN Code是否合法 The algorithm to validate the checksum is given in C code below.

/**
 * wps_pin_valid - Check whether a PIN has a valid checksum
 * @pin: Eight digit PIN (i.e., including the checksum digit)
 * Returns: 1 if checksum digit is valid, or 0 if not
 */
unsigned int wps_pin_valid(unsigned int pin)
{
 return wps_pin_checksum(pin / 10) == (pin % 10);
}

3. 參考來源
http://ftp.netbsd.org/pub/NetBSD/NetBSD-release-6/src/external/bsd/wpa/dist/src/wps/wps_common.c