A PHP class to encrypt and decrypt strings using a static application secret. Input is converted to hex strings to enable easier handling

Cryptor.php

<?php

namespace Vendor\Library;

use function bin2hex;
use function hex2bin;
use function openssl_decrypt;
use function openssl_encrypt;
use function random_bytes;

/**
 * Cryptor class
 *
 * The encrypt/decrypt methods are largely taken from here:
 *
 * @link https://stackoverflow.com/a/46872528/2532203
 */
class Cryptor
{
    /**
     * Holds the encryption algorithm to use
     */
    protected const ENCRYPTION_ALGORITHM = 'AES-256-CBC';

    /**
     * Holds the hash algorithm to use
     */
    protected const HASHING_ALGORITHM = 'sha256';

    /**
     * Holds the application encryption secret
     *
     * @var string
     */
    protected $secret;

    /**
     * Cryptor constructor
     *
     * @param string $secret application encryption secret
     */
    public function __construct(string $secret)
    {
        $this->secret = $secret;
    }

    /**
     * Decrypts a string using the application secret.
     *
     * @param string $input hex representation of the cipher text
     *
     * @return string UTF-8 string containing the plain text input
     */
    public function decrypt(string $input): string
    {
        // prevent decrypt failing when $input is not hex or has odd length
        // added via suggestion from @markusand, see comment:
        // https://gist.github.com/Radiergummi/b326219f55edb33759791a78a1c134c3#gistcomment-2803128
        if (strlen($input) % 2 || ! ctype_xdigit($input)) {
            return '';
        }

        // we'll need the binary cipher
        $binaryInput = hex2bin($input);
        $iv = substr($binaryInput, 0, 16);
        $hash = substr($binaryInput, 16, 32);
        $cipherText = substr($binaryInput, 48);
        $key = hash(self::HASHING_ALGORITHM, $this->secret, true);

        // if the HMAC hash doesn't match the hash string, something has gone wrong
        if (hash_hmac(self::HASHING_ALGORITHM, $cipherText, $key, true) !== $hash) {
            return '';
        }

        return openssl_decrypt(
            $cipherText,
            self::ENCRYPTION_ALGORITHM,
            $key,
            OPENSSL_RAW_DATA,
            $iv
        );
    }

    /**
     * Encrypts a string using the application secret. This returns a hex representation of the binary cipher text
     *
     * @param string $input plain text input to encrypt
     *
     * @return string hex representation of the binary cipher text
     * @throws \Exception
     */
    public function encrypt(string $input): string
    {
        $key = hash(self::HASHING_ALGORITHM, $this->secret, true);
        $iv = random_bytes(16);

        $cipherText = openssl_encrypt(
            $input,
            self::ENCRYPTION_ALGORITHM,
            $key,
            OPENSSL_RAW_DATA,
            $iv
        );
        $hash = hash_hmac(self::HASHING_ALGORITHM, $cipherText, $key, true);

        return bin2hex($iv . $hash . $cipherText);
    }
}

Sorry, I've got no idea what CI 2/3 is?

sorry, it's Codeigniter i mean. i have no idea implement this, put as thirt_party or libraries it' self.

Hello.
Decrypt not working in PHP 7.2.
Error, return '':
if (hash_hmac(self::HASHING_ALGORITHM, $cipherText, $key, true) !== $hash) {
return '';
}
Works well in php 7.4.
How to be?

Support for PHP 7.2 ended years ago - if it does in 7.4, that's your best option 🤷‍♂️

We can't switch to the older version of PHP yet (a lot of legacy code). Can you suggest what could be the issue?