ctr_slice_iv_openssl.php

<?php
$d = "000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f";
$k = "k0k1k2k3k4k5k6k7"; // 16 byte AES key
$bs = 16; // 16 byte block size

$iv = mcrypt_create_iv($bs);
$ct = openssl_encrypt($d, "aes-128-ctr", $k, OPENSSL_RAW_DATA, $iv);

$dec_offset = 32;
$ct_slice = substr($ct, $dec_offset);

$iv_slice = add($iv, $dec_offset / $bs);

$d_slice = openssl_decrypt($ct_slice, "aes-128-ctr", $k, OPENSSL_RAW_DATA, $iv_slice);

var_dump($d_slice);

function add($big_num_str, $to_add){
    $big_num = str_split(strrev($big_num_str));
    for($i = 0; $i < count($big_num) ; $i++){
        $tmp = ord($big_num[$i]) + $to_add;
        $big_num[$i] = $tmp % 256;
        $to_add = floor( $tmp / 256 );
    }
    while($to_add){
        $big_num[$i++] = $to_add % 256;
        $to_add = floor( $to_add / 256 );
    }
    for($i = 0; $i < count($big_num) ; $i++){
        $big_num[$i] = chr($big_num[$i]);
    }
    return strrev(implode('', $big_num) );
}