How Can I Encrypt and Decrypt Strings in PHP Securely?

How do you Encrypt and Decrypt a PHP String?

Encrypting a PHP string involves converting the original string into an encrypted format using a key or salt. Decrypting the string requires the same key or salt to retrieve the original string.

Encryption Process

1. Encrypt: Encrypt the original string using a secure algorithm like AES-256 in CTR (Counter Mode) or GCM (Galois/Counter Mode).
2. Authenticate: Compute a MAC (Message Authentication Code) for the encrypted string using HMAC-SHA-256. Combine the encrypted string and the MAC to generate the final encrypted result.

Decryption Process

1. Authenticate: Recalculate the MAC for the encrypted result and compare it to the MAC included. Abort if they differ.
2. Decrypt: Decrypt the encrypted string using the correct key.

Key Considerations

• Use authenticated encryption algorithms (e.g., AES-GCM, ChaCha20-Poly1305) for both encryption and authentication.
• Utilize secure libraries like libsodium or defuse/php-encryption for robust encryption and decryption functionality.
• Avoid rolling your own cryptography due to potential security risks.
• Generate IVs (initialization vectors) using a CSPRNG (Cryptographically Secure Pseudo-Random Number Generator) like random_bytes or sodium_randombytes.
• Protect encryption keys with caution. Consider using a key encryption key or a secure key management system.

Example using Libsodium:

<?php
use Sodium\Crypto;

function encrypt(string $message, string $key): string
{
    $nonce = random_bytes(Crypto::SECRETBOX_NONCEBYTES);
    $encrypted = Crypto::secretbox($message, $nonce, $key);
    return base64_encode($nonce . $encrypted);
}

function decrypt(string $encrypted, string $key): string
{
    $decoded = base64_decode($encrypted);
    $nonce = substr($decoded, 0, Crypto::SECRETBOX_NONCEBYTES);
    $ciphertext = substr($decoded, Crypto::SECRETBOX_NONCEBYTES);
    $decrypted = Crypto::secretbox_open($ciphertext, $nonce, $key);
    
    return $decrypted;
}

$message = 'Hello, world!';
$key = random_bytes(Crypto::SECRETBOX_KEYBYTES);
$encrypted = encrypt($message, $key);
$decrypted = decrypt($encrypted, $key);

var_dump($encrypted);
var_dump($decrypted);

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