<?php

function encode($string, $alphabet)
{
 foreach(str_split(strtolower($string)) as $char)
 {
  @$resp .= $alphabet[$char];
 }

 return $resp;
}

function decode($string, $alphabet) 
{
 foreach(str_split(strtolower($string)) as $char)
 {
  foreach($alphabet as $c => $r)
  {
   if ($char == $r) @$resp .= $c;
  }
 }

 return $resp;
}

$a = range('a', 'z', 2);

foreach(range('a', 'z') as $char)
{
 if (!in_array($char, $a)) $a[] = $char;
}


for ($c=0; $c<=25; $c++)
{
 @$alphabet[range('a', 'z')[$c]] = $a[$c];
}

$alphabet[' '] = ' ';

echo encode('my name is dan', $alphabet) . "\n"; // yx bayi ql gab
echo decode('yx bayi ql gab', $alphabet);