PHP: How to hash the visitor IP irreversibly for privacy?

[Fli]

I have asked a HuggingChat AI a question:

Is it true that a PHP website developer can record website visitor IP and turn it into a hash for privacy and then when the website code and database with these hashes is leaked, such hashes can not be converted back to IP? If so, can you link me to a detail, like PHP functions or libraries or methods that achieve this?

Its answer was:

Yes, it is true that a PHP website developer can record website visitor IP addresses and store them as hashes to protect user privacy. This process is called "hashing" or "one-way hashing".

Hashing is a cryptographic technique that takes input data (in this case, the IP address) and produces a fixed-size string of characters, known as a "hash" or "digest", that cannot be reversed or converted back to the original input data.

When a website stores hashed IP addresses, it's much harder for an attacker to obtain the original IP addresses, even if the database is leaked or compromised. This is because the hashing process is designed to be one-way, meaning it's easy to generate a hash from the original data, but impossible to recreate the original data from the hash.

In PHP, there are several libraries and functions that can be used to hash IP addresses. Here are a few examples:

1. `hash()` function: PHP's built-in `hash()` function can be used to generate a hash from an IP address. You can use a hashing algorithm like `sha256` or `sha512` to generate a secure hash.

Example:

php
$ip_address = '192.168.1.100';
$hashed_ip = hash('sha256', $ip_address);

2. `hash_hmac()` function: This function generates a keyed hash using the HMAC (Keyed-Hashing for Message Authentication) algorithm.

Example:

php
$ip_address = '192.168.1.100';
$key = 'your_secret_key_here';
$hashed_ip = hash_hmac('sha256', $ip_address, $key);

3. `password_hash()` function: This function is specifically designed for password hashing, but can also be used to hash IP addresses". It uses the Argon2 algorithm by default.

Example:

php
$ip_address = '192.168.1.100';
$hashed_ip = password_hash($ip_address, PASSWORD_ARGON2I);

4. `hashids` library: This is a popular PHP library for generating and verifying hashes. It uses a combination of hashing algorithms and base62 encoding to generate a compact, URL-safe hash.

Example:

php
use Hashids\Hashids;

$ip_address = '192.168.1.100';
$hashids = new Hashids('your_secret_key', 10);
$hashed_ip = $hashids->encode($ip_address);

Some important notes:

* Always use a secure hashing algorithm, such as `sha256` or `sha512`, and a sufficient salt value (if using `password_hash()`).
* Store the hashed IP addresses securely in your database, using a secure connection and proper data encryption.
* Keep your secret keys and salts secure, as they can be used to reverse-engineer the hashes.
* Consider using additional security measures, such as IP anonymization or geolocation-based hashing, to further protect user privacy.

Here are some detailed resources on hashing and IP address anonymization:

* [Hashing and salting](https://owasp.org/www-project-cheat-sheets/cheatsheets/Password_Storage_Cheat_Sheet.html)
* [IP address anonymization](https://www.owasp.org/index.php/IP_Address_Anonymization)
* [Hashids library documentation](https://hashids.org/php/)

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My follow-up question would be:

Are you sure that this IP hashing can be done irreversibly? I think that it is trivial to crease hashes for all known IPs and that way reverse hash back to IP? I mean when an attacker knows the way the hash has been created (database, site data is leaked, handed over). I mean the hashing should be done the way that even the site operator can not reverse it (using some private key, salt)?

AI reply (which i think is still problematic since if the PHP code is leaked/handed over, then the secret salt is known and the hash can be reversed?):

$fixed_salt = 'your_secret_salt_value_here';
$ip_address = '192.168.1.100';
$hashed_ip = hash('sha256', $ip_address. $fixed_salt);