由于mcrypt是一种废弃软件，不再建议使用，因此这里是使用openssl的示例。

class AES256Encryption
{
    public const BLOCK_SIZE = 8;
    public const IV_LENGTH = 16;
    public const CIPHER = 'AES256';

    public static function generateIv(bool $allowLessSecure = false): string
    {
        $success = false;
        $random = openssl_random_pseudo_bytes(openssl_cipher_iv_length(static::CIPHER));
        if (!$success) {
            if (function_exists('sodium_randombytes_random16')) {
                $random = sodium_randombytes_random16();
            } else {
                try {
                    $random = random_bytes(static::IV_LENGTH);
                }
                catch (Exception $e) {
                    if ($allowLessSecure) {
                        $permitted_chars = implode(
                            '',
                            array_merge(
                                range('A', 'z'),
                                range(0, 9),
                                str_split('~!@#$%&*()-=+{};:"<>,.?/\'')
                            )
                        );
                        $random = '';
                        for ($i = 0; $i < static::IV_LENGTH; $i++) {
                            $random .= $permitted_chars[mt_rand(0, (static::IV_LENGTH) - 1)];
                        }
                    }
                    else {
                        throw new RuntimeException('Unable to generate initialization vector (IV)');
                    }
                }
            }
        }
        return $random;
    }

    protected static function getPaddedText(string $plainText): string
    {
        $stringLength = strlen($plainText);
        if ($stringLength % static::BLOCK_SIZE) {
            $plainText = str_pad($plainText, $stringLength + static::BLOCK_SIZE - $stringLength % static::BLOCK_SIZE, "\0");
        }
        return $plainText;
    }

    public static function encrypt(string $plainText, string $key, string $iv): string
    {
        $plainText = static::getPaddedText($plainText);
        return base64_encode(openssl_encrypt($plainText, static::CIPHER, $key, OPENSSL_RAW_DATA, $iv));
    }

    public static function decrypt(string $encryptedText, string $key, string $iv): string
    {
        return openssl_decrypt(base64_decode($encryptedText), static::CIPHER, $key, OPENSSL_RAW_DATA, $iv);
    }
}

$text = '8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql';
$key = 'secretkey';
$iv = AES256Encryption::generateIv();
$encryptedText = AES256Encryption::encrypt($text, $key, $iv);
$decryptedText = AES256Encryption::decrypt($encryptedText, $key, $iv);

printf('Original Text: %s%s', $text, PHP_EOL);
printf('Encrypted: %s%s', $encryptedText, PHP_EOL);
printf('Decrypted: %s%s', $decryptedText, PHP_EOL);

输出：

// Long string with lots of different characters
Original Text: 8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql
Encrypted    : rsiF4PMCMyvAp+CTuJrxJYGoV4BSy8Fy+q+FL8m64+Mt5V3o0HS0elRkWXsy+//hPjzNhjmVktxVvMY55Negt4DyLcf2QpH05wUX+adJDe634J/9fWd+nlEFoDutXuhY+/Kep9zUZFDmLmszJaBHWQ==
Decrypted    : 8SViI0Gz4r-p7A15YxkwjOBFuW*@NTtbm{U]D&E=~6yLM+adX'P;h3$,KJ%/eo>}<Rs:2#gZ.9fqn"Cv_^[(H\c!)?`Ql

旧答案

尝试使用此PHP5类使用mcrypt进行加密。在这种情况下，它使用的是AES加密。您需要为使用它的每个站点更改密钥。如果您至少不使用它，它可能会指导您编写自己的版本。

<?php

class Encryption
{
    const CIPHER = MCRYPT_RIJNDAEL_128; // Rijndael-128 is AES
    const MODE   = MCRYPT_MODE_CBC;

    /* Cryptographic key of length 16, 24 or 32. NOT a password! */
    private $key;
    public function __construct($key) {
        $this->key = $key;
    }

    public function encrypt($plaintext) {
        $ivSize = mcrypt_get_iv_size(self::CIPHER, self::MODE);
        $iv = mcrypt_create_iv($ivSize, MCRYPT_DEV_URANDOM);
        $ciphertext = mcrypt_encrypt(self::CIPHER, $this->key, $plaintext, self::MODE, $iv);
        return base64_encode($iv.$ciphertext);
    }

    public function decrypt($ciphertext) {
        $ciphertext = base64_decode($ciphertext);
        $ivSize = mcrypt_get_iv_size(self::CIPHER, self::MODE);
        if (strlen($ciphertext) < $ivSize) {
            throw new Exception('Missing initialization vector');
        }

        $iv = substr($ciphertext, 0, $ivSize);
        $ciphertext = substr($ciphertext, $ivSize);
        $plaintext = mcrypt_decrypt(self::CIPHER, $this->key, $ciphertext, self::MODE, $iv);
        return rtrim($plaintext, "\0");
    }
}

用法：

$key = /* CRYPTOGRAPHIC!!! key */;
$crypt = new Encryption($key);
$encrypted_string = $crypt->encrypt('this is a test');
$decrypted_string = $crypt->decrypt($encrypted_string); // this is a test

笔记：

• 此类不适用于二进制数据（可能以NUL字节结尾）
• 此类不提供经过身份验证的加密。