Practical summary of PHP bloom filter used to prevent DDoS attacks

Practical Summary of PHP Bloom Filters Used to Prevent DDoS Attacks

With the rapid development of the Internet, network attacks have become more and more common. Among them, DDoS attack is a common attack method. Its purpose is to occupy server resources through a large number of requests, causing the target server to fail to operate normally. In order to deal with this type of attack, developers can use Bloom Filter to improve the server's ability to resist attacks.

The Bloom filter is a fast and efficient data structure that can be used to determine whether an element exists in a collection. Compared with traditional data structures such as arrays or hash tables, Bloom filters have lower time and space complexity when determining whether an element exists. It is suitable for finding and filtering large-scale data sets.

The following is a practical summary of how to use PHP's bloom filter to prevent DDoS attacks:

1. Download and install the bloom filter library

First, we need to download and install PHP’s bloom filter library. You can use tools such as Composer to manage dependencies and introduce bloom filter libraries.

composer require brianium/parblooom

2. Create a Bloom filter instance

Before using a Bloom filter, we need to create an instance of the Bloom filter. Bloom filters can be initialized by choosing an appropriate error probability and expected number of elements.

use BrianiumParblooomParblooom;

// 初始化布隆过滤器
$falsePositiveProbability = 0.01; // 错误概率为1%
$expectedNumberOfElements = 1000; // 预期元素数量为1000个
$bloomFilter = new Parblooom($falsePositiveProbability, $expectedNumberOfElements);

3. Add the request IP to the bloom filter

Before processing each request, we need to add the requested IP address to the bloom filter. This can quickly determine whether the IP has been added and handle it accordingly.

// 添加请求IP到布隆过滤器中
$requestIP = $_SERVER['REMOTE_ADDR'];
$bloomFilter->add($requestIP);

4. Determine whether the requested IP exists in the Bloom filter

Next, we need to determine whether the requested IP address already exists when processing each request. in Bloom filter. If it exists, it means that the IP has been added and needs to be processed accordingly, such as rejecting the request.

// 判断请求IP是否存在于布隆过滤器中
$requestIP = $_SERVER['REMOTE_ADDR'];
if ($bloomFilter->exists($requestIP)) {
    // IP已经存在于布隆过滤器中，拒绝该请求
    http_response_code(403);
    echo "Access Denied";
    exit;
} else {
    // IP不存在于布隆过滤器中，继续处理请求
    // ...
}

Through the above practical summary, we can see that it is very simple to use PHP Bloom filter to prevent DDoS attacks. By adding the requested IP address to the Bloom filter and determining whether the IP already exists in the Bloom filter when processing each request, duplicate requests and malicious requests can be effectively prevented.

It should be noted that the Bloom filter cannot determine 100% accurately whether an element exists in the set, and it has a certain probability of error. Therefore, in practical applications, we need to choose the appropriate error probability and expected number of elements based on specific needs.

In short, PHP bloom filter is a simple and efficient tool to defend against DDoS attacks. By properly using Bloom filters, we can improve the server's ability to resist attacks and ensure the normal operation of the system.

Reference:

1. [PHP Bloom Filter Library](https://github.com/brianium/parbloom)
2. [Bloom filter - Wikipedia]( https://en.wikipedia.org/wiki/Bloom_filter)

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