Webform comfirmation page token
I found the answer in the webform.module file:

/**
 * Return the access token for a submission.
 *
 * @param object $submission
 *   The submission object.
 *
 * @return string
 *   The access token for the submission.
 */
function webform_get_submission_access_token($submission) {
  return md5($submission-&gt;submitted . $submission-&gt;sid . drupal_get_private_key());
}


So it's an MD5 hash of a concatenation of the submission date, submission ID and a random private key, set by the webform module.