Complete Guide to PHP Data Encryption and Decryption: Symmetric, Asymmetric, and Hashing Methods

Introduction

In the modern internet environment, data security is critical. To protect sensitive information, developers often need to encrypt and decrypt data. PHP, as a popular server-side language, offers a variety of encryption functions and libraries that support multiple algorithms. This article explains how to implement data encryption and decryption in PHP with practical code examples.

Using Symmetric Encryption

Symmetric encryption is the most common method, also called shared key encryption. The same key is used for both encryption and decryption. PHP supports algorithms such as AES, DES, and 3DES. Here's an example using AES-256-CBC:

function encrypt($data, $key) {
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-256-cbc'));
    $encrypted = openssl_encrypt($data, 'aes-256-cbc', $key, 0, $iv);
    return base64_encode($iv . $encrypted);
}

function decrypt($data, $key) {
    $data = base64_decode($data);
    $iv = substr($data, 0, openssl_cipher_iv_length('aes-256-cbc'));
    $encrypted = substr($data, openssl_cipher_iv_length('aes-256-cbc'));
    return openssl_decrypt($encrypted, 'aes-256-cbc', $key, 0, $iv);
}

$key = 'secret_key';
$data = 'sensitive_data';

$encryptedData = encrypt($data, $key);
echo 'Encrypted data: ' . $encryptedData . PHP_EOL;

$decryptedData = decrypt($encryptedData, $key);
echo 'Decrypted data: ' . $decryptedData . PHP_EOL;

Explanation:

• The encrypt function uses openssl_encrypt to encrypt the data and base64_encode to convert it into a readable string.
• The decrypt function decodes the base64 string, extracts the IV and encrypted content, and then uses openssl_decrypt to decrypt it.
• openssl_cipher_iv_length returns the IV length for the specified algorithm.

Using Asymmetric Encryption

Asymmetric encryption uses a pair of keys: a public key for encryption and a private key for decryption. PHP supports algorithms such as RSA. Example:

function encrypt($data, $publicKey) {
    openssl_public_encrypt($data, $encrypted, $publicKey);
    return base64_encode($encrypted);
}

function decrypt($encryptedData, $privateKey) {
    openssl_private_decrypt(base64_decode($encryptedData), $decrypted, $privateKey);
    return $decrypted;
}

$publicKey = openssl_pkey_get_public('file://path/to/public_key.pem');
$privateKey = openssl_pkey_get_private('file://path/to/private_key.pem');

$data = 'sensitive_data';

$encryptedData = encrypt($data, $publicKey);
echo 'Encrypted data: ' . $encryptedData . PHP_EOL;

$decryptedData = decrypt($encryptedData, $privateKey);
echo 'Decrypted data: ' . $decryptedData . PHP_EOL;

Explanation:

• The encrypt function uses openssl_public_encrypt to encrypt data and base64_encode to convert it to a string.
• The decrypt function decodes the base64 string to binary and then decrypts it with openssl_private_decrypt.

Using Hash Functions

Hash functions map data of arbitrary length to a fixed-length hash, typically for integrity verification rather than encryption. PHP supports MD5, SHA1, SHA256, etc. Example:

$data = 'sensitive_data';

$hashedData = md5($data);
echo 'Hashed data: ' . $hashedData . PHP_EOL;

Explanation:

• The md5 function computes the MD5 hash of the given data.

Conclusion

This article introduced how to implement data encryption and decryption in PHP, covering symmetric encryption, asymmetric encryption, and hash functions, with full code examples. Using these methods, developers can effectively protect sensitive data during transmission and storage.