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Dave Pearson (dave at pds-uk dot com) ¶
9 years ago
Here's my final version of a GUIDv4 function (based on others work here) that should work on all platforms and gracefully fallback to less cryptographically secure version if others are not supported...

<?php
/**
 * Returns a GUIDv4 string
 *
 * Uses the best cryptographically secure method 
 * for all supported pltforms with fallback to an older, 
 * less secure version.
 *
 * @param bool $trim
 * @return string
 */
function GUIDv4 ($trim = true)
{
    // Windows
    if (function_exists('com_create_guid') === true) {
        if ($trim === true)
            return trim(com_create_guid(), '{}');
        else
            return com_create_guid();
    }

    // OSX/Linux
    if (function_exists('openssl_random_pseudo_bytes') === true) {
        $data = openssl_random_pseudo_bytes(16);
        $data[6] = chr(ord($data[6]) & 0x0f | 0x40);    // set version to 0100
        $data[8] = chr(ord($data[8]) & 0x3f | 0x80);    // set bits 6-7 to 10
        return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($data), 4));
    }

    // Fallback (PHP 4.2+)
    mt_srand((double)microtime() * 10000);
    $charid = strtolower(md5(uniqid(rand(), true)));
    $hyphen = chr(45);                  // "-"
    $lbrace = $trim ? "" : chr(123);    // "{"
    $rbrace = $trim ? "" : chr(125);    // "}"
    $guidv4 = $lbrace.
              substr($charid,  0,  8).$hyphen.
              substr($charid,  8,  4).$hyphen.
              substr($charid, 12,  4).$hyphen.
              substr($charid, 16,  4).$hyphen.
              substr($charid, 20, 12).
              $rbrace;
    return $guidv4;
}
?>
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