When uniqid is too slow in PHP

Jun 8, 2010 php
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I just profiled some of my code and found out that the biggest chunk of my processing time was used by uniqid(). I use this to generate form tokens to prevent cross site request forgeries. On one page, I have 6 forms each with its own unique uniqid().

The first thought is to just use one ID per page. However, I didn’t want to change too much of my code. It’s working - so let’s just make it work faster. I did some thinking and realized that maybe my unique id didn’t need to be THAT unique - just not super predictable. A sha1() hash of a random number should do the trick. And it should be faster. Just to verify, I did my own benchmark using this code:

$start = $stop = array();

$start['uniqid'] = microtime(TRUE);
for ($x = 0; $x< 1000; $x++) {
  $val = uniqid();
$stop['uniqid'] = microtime(TRUE);

$start['mt_rand'] = microtime(TRUE);
for ($x=0; $x<1000; $x++) {
  $val = mt_rand(0, 1000000);
$stop['mt_rand'] = microtime(TRUE);

$start['sha1/mt_rand'] = microtime(TRUE);
for ($x=0; $x<1000; $x++) {
  $val = sha1(mt_rand(0, 1000000));
$stop['sha1/mt_rand'] = microtime(TRUE);

foreach ($start as $key=>$startval) {
  echo "{$key}: " . ($stop[$key] - $startval) . "<br></br>";

The results:

uniqid: 1.1227629184723
mt_rand: 0.0030300617218018
sha1/mt_rand: 0.0076968669891357

As you can see, sha1/mt_rand combination is so much faster. In fact, 140x! While this is still micro-optimization, running that 6 times to me makes a difference.

Your thoughts? Is this still unique enough for form tokens?

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