This function will convert "cn=bryan,ou=users,ou=admin,o=apachetoolbox" to "bryan,users,admin,apachetoolbox".

The function of bryan will only work if you start with an Organization and using only an Organizational Unit as a container and the object is an CN.

For example:

$DN = "CN=DNS,CN=Authorized Login Methods,CN=Security";

echo ($DN = ldap_dn2ufn($DN)) . "\n";

echo ($DN = ldap_ufn2dn($DN)) . "\n";

will echo:

DNS,Authorized Login Methods,Security

CN=DNS,OU=Authorized Login Methods,O=Security

function ldap_unf2dn($unf,$delimeter=".") {
 $seperated = explode($delimeter,$unf); //split the unf up by the given delimeter
 $LastKey=count($seperated)-1;          //0 is the first key to total-1 would be the last key               
 foreach($seperated as $key => $value) {
  if ($key == 1) {              //first variable is the CN
   $dn="${dn}cn=$value,";
  } elseif ($key == $LastKey) { //last variable, so it's the O
   $dn="${dn}o=$value";
  } elseif ($value == "") {     //value is blank, so continue
   continue;
  } else {                      //just a typical OU
   $dn="${dn}ou=$value,";
  }
   
 };
return $dn;

}

$unf=".bryan.users.admin.apachetoolbox"; 
$dn=ldap_unf2dn($unf);
print "$dn" // will give me "cn=bryan,ou=users,ou=TS,o=apachetoolbox"

Don't know if anyone is interested in this, but this is a modified and more dynamic version of the posting below. Since ldap_dn2ufn takes ',' as delimiter for the UFNs, we'll also use it here. $pHowToBuild specifies, how the DN is going to be build. 

Short example:

$myUFN = ldap_dn2ufn("cn=naaina, ou=container1, ou=container2, ou=container3, o=private, c=de");
echo $myUFN . "\n"; // will return "naaina, container1, container2, container3, private, de"

$myDN = $ldapObject->conv_ufn2dn($myUFN);
echo $myDN . "\n"; // will return "cn=naaina,ou=container1,ou=container2,ou=container3,o=private,c=de"

For the object name, $pHowToBuild["object"] is going to be used as prefix - for containers $pHowToBuild["container"] and for the last n elements $pHowToBuild["last"].

<?php
  function ldap_ufn2dn (
   $pUFN,
   $pDelimiter = ",",
   $pHowToBuild = array(
    "object" => "cn",
    "container" => "ou",
    "last" => array("o", "c")
   )
  ) 
  {
   $resultDN = null;
   
   if(!empty($pUFN)) {
     /* Check $pHowToBuild */
     if(is_array($pHowToBuild)) { 
       /* Check if required keys are existent */
       if(array_key_exists("object", $pHowToBuild) &&
          array_key_exists("container", $pHowToBuild) &&
          array_key_exists("last", $pHowToBuild)) 
       {
         $ufnArray = explode($pDelimiter, $pUFN);
         $ufnLast  = count($ufnArray) - count($pHowToBuild["last"]); 

         /* Remove empty values */          
         foreach($ufnArray as $objKey => $objVal)
           if(empty($objVal))
             array_splice($ufnArray, $objKey, 1);
         
         /* Now build the DN ... */
         foreach($ufnArray as $objKey => $objVal) {
           $objVal = trim($objVal);
        
           if($objKey == 0) { 
             /* For the object */
             $resultDN .= $pHowToBuild["object"] . "=" . $objVal . ",";
           } elseif ($objKey >= $ufnLast) { 
             /* For last parts of the DN */
             $resultDN .= $pHowToBuild["last"][$objKey - $ufnLast] . "=" . $objVal;
             if(($objKey - $ufnLast - 1) != 0) {
               $resultDN .= ",";
             }
           } else { 
             /* For containers */
             $resultDN .= $pHowToBuild["container"] . "=" . $objVal . ",";
           }
         }
       } 
     }    
   } 
   
   return $resultDN;
  }
?>