Validate Social Security Number SSN

ValidateSSN.php

/**
 * Validate SSN - must be in format AAA-GG-SSSS or AAAGGSSSS
 *
 * @param $ssn
 * @return bool
 */
function validate_ssn($ssn) {

    $ssnTrimmed = trim($ssn);

    // Must be in format AAA-GG-SSSS or AAAGGSSSS
    if ( ! preg_match("/^([0-9]{9}|[0-9]{3}-[0-9]{2}-[0-9]{4})$/", $ssnTrimmed)) {
        return false;
    }

    // Split groups into an array
    $ssnFormatted = (strlen($ssnTrimmed) == 9) ? preg_replace("/^([0-9]{3})([0-9]{2})([0-9]{4})$/", "$1-$2-$3", $ssnTrimmed) : $ssnTrimmed;
    $ssn_array = explode('-', $ssnFormatted);

    // number groups must follow these rules:
    // * no single group can have all 0's
    // * first group cannot be 666, 900-999
    // * second group must be 01-99
    // * third group must be 0001-9999

    foreach ($ssn_array as $group) {
        if ($group == 0) {
            return false;
        }
    }

    if ($ssn_array[0] == 666 || $ssn_array[0] > 899) {
        return false;
    }

    return true;
}