PHP7中基于特定盐值的最简安全加解密方案咨询

Hey there! Since mcrypt_encrypt got deprecated back in PHP 7.1, the go-to secure replacement is the built-in OpenSSL extension—it’s well-maintained, widely supported, and ticks all your boxes for reversible encryption with a specific salt. We’ll use AES-256-GCM here because it provides authenticated encryption (meaning it verifies your data hasn’t been tampered with), which is way more secure than older modes like CBC or ECB.

Implementation Code #

Below are two straightforward functions for encryption and decryption. They use your specific salt to derive a secure key, generate a random IV (initialization vector) for each encryption, and bundle all necessary data (IV, ciphertext, and authentication tag) into a single base64-encoded string for easy storage/transmission.

Encryption Function #

function encrypt(string $plaintext, string $salt): string {
    $cipher = 'aes-256-gcm';
    $ivLength = openssl_cipher_iv_length($cipher);
    
    // Generate a unique random IV for each encryption (critical for security)
    $iv = openssl_random_pseudo_bytes($ivLength);
    
    // Derive a 256-bit secure key from your salt using PBKDF2 (slow hashing to resist brute force)
    $key = hash_pbkdf2('sha256', $salt, $iv, 10000, 32, true);
    
    // Encrypt the plaintext and generate an authentication tag
    $ciphertext = openssl_encrypt(
        $plaintext,
        $cipher,
        $key,
        OPENSSL_RAW_DATA,
        $iv,
        $tag
    );
    
    // Bundle IV, tag, and ciphertext, then base64 encode for safe storage
    return base64_encode($iv . $tag . $ciphertext);
}

Decryption Function #

function decrypt(string $encryptedData, string $salt): string|false {
    $cipher = 'aes-256-gcm';
    $ivLength = openssl_cipher_iv_length($cipher);
    $tagLength = 16; // Standard tag length for GCM mode
    
    // Decode the base64-encoded encrypted data
    $decodedData = base64_decode($encryptedData);
    if (!$decodedData) return false;
    
    // Extract IV, authentication tag, and ciphertext from the decoded bundle
    $iv = substr($decodedData, 0, $ivLength);
    $tag = substr($decodedData, $ivLength, $tagLength);
    $ciphertext = substr($decodedData, $ivLength + $tagLength);
    
    // Derive the same key using the salt and IV
    $key = hash_pbkdf2('sha256', $salt, $iv, 10000, 32, true);
    
    // Decrypt and verify the data (fails if tampered with or wrong salt)
    $plaintext = openssl_decrypt(
        $ciphertext,
        $cipher,
        $key,
        OPENSSL_RAW_DATA,
        $iv,
        $tag
    );
    
    return $plaintext;
}

How to Use #

// Your specific secret salt (keep this safe—treat it like a password!)
$specificSalt = 'my-super-secret-salt-that-is-at-least-32-characters-long';

// Encrypt a string
$originalString = 'This is my confidential message!';
$encrypted = encrypt($originalString, $specificSalt);
echo "Encrypted Output: $encrypted\n";

// Decrypt the data back to the original string
$decrypted = decrypt($encrypted, $specificSalt);
echo "Decrypted Result: $decrypted\n"; // Should match the original string

Critical Security Notes #

• Guard your salt like a password: Never hardcode it in public code repositories. Store it in environment variables or secure, non-public config files.
• Use a long salt: Aim for at least 32 characters (256 bits) to make brute-force attacks impractical.
• IVs are random and unique: The code generates a new IV every time you encrypt, so identical plaintexts will produce different ciphertexts—this prevents pattern detection attacks.
• AES-256-GCM ensures integrity: If the encrypted data is tampered with or you use the wrong salt, decrypt() will return false, so always add error handling for this case.
• PBKDF2 slows down key derivation: The 10,000 iterations make it harder for attackers to guess your salt via brute-force. You can adjust this number (higher = more secure, but slightly slower).

内容的提问来源于stack exchange，提问作者Attila Naghi