Simple PHP Encryption & Decryption

encrypt-decrypt.php

<?php

/**
 * Simple PHP Encryption functions
 *
 * Attempts to be as secure as possible given:
 *
 * - Key can be any string
 * - No knowledge of encryption is required
 * - Only key and raw/encrypted string is needed at each end
 * - Metadata can be anything (string, array, etc.)
 *
 * If possible, always prefer a library like https://github.com/defuse/php-encryption
 * and only use these functions if that isn't possible
 *
 * Adapted from http://stackoverflow.com/a/30239440/1562799
 */

/**
 * Encrypts a string
 *
 * @param string $key  Encryption key, also required for decryption
 * @param string $raw  Raw string to be encrypted
 * @param mixed  $meta Associated data that must be provided during decryption
 *
 * @return string Raw data encrypted with key
 */
function encrypt( $key, $plaintext, $meta = '' ) {

	// Generate valid key
	$key = hash_pbkdf2( 'sha256', $key, '', 10000, 0, true );

	// Serialize metadata
	$meta = serialize($meta);

	// Derive two subkeys from the original key
	$mac_key = hash_hmac( 'sha256', 'mac', $key, true );
	$enc_key = hash_hmac( 'sha256', 'enc', $key, true );
	$enc_key = substr( $enc_key, 0, 32 );

	// Derive a "synthetic IV" from the nonce, plaintext and metadata
	$temp = $nonce = ( 16 > 0 ? mcrypt_create_iv( 16 ) : "" );
	$temp .= hash_hmac( 'sha256', $plaintext, $mac_key, true );
	$temp .= hash_hmac( 'sha256', $meta, $mac_key, true );
	$mac = hash_hmac( 'sha256', $temp, $mac_key, true );
	$siv = substr( $mac, 0, 16 );

	// Encrypt the message
	$enc = mcrypt_encrypt( 'rijndael-128', $enc_key, $plaintext, 'ctr', $siv );
	return base64_encode( $siv . $nonce . $enc );

}

/**
 * Decrypts an encrypted string
 *
 * @param string $key       Encryption key, also used during encryption
 * @param string $encrypted Encrypted string to be decrypted
 * @param mixed  $meta      Associated data that must be the same as when encrypted
 *
 * @return string Decrypted string or `null` if key/meta has been tampered with
 */
function decrypt( $key, $ciphertext, $meta = '' ) {

	// Generate valid key
	$key = hash_pbkdf2( 'sha256', $key, '', 10000, 0, true );

	// Serialize metadata
	$meta = serialize($meta);

	// Derive two subkeys from the original key
	$mac_key = hash_hmac( 'sha256', 'mac', $key, true );
	$enc_key = hash_hmac( 'sha256', 'enc', $key, true );
	$enc_key = substr( $enc_key, 0, 32 );

	// Unpack MAC, nonce and encrypted message from the ciphertext
	$enc = base64_decode( $ciphertext );
	$siv = substr( $enc, 0, 16 );
	$nonce = substr( $enc, 16, 16 );
	$enc = substr( $enc, 16 + 16 );

	// Decrypt message
	$plaintext = mcrypt_decrypt( 'rijndael-128', $enc_key, $enc, 'ctr', $siv );

	// Verify MAC, return null if message is invalid
	$temp = $nonce;
	$temp .= hash_hmac( 'sha256', $plaintext, $mac_key, true );
	$temp .= hash_hmac( 'sha256', $meta, $mac_key, true );
	$mac = hash_hmac( 'sha256', $temp, $mac_key, true );
	if ( $siv !== substr( $mac, 0, 16 ) ) return null;

	return $plaintext;

}

/**
 * Encrypts a string
 *
 * Do not use this function, it is only here for historical reference
 *
 * @param string $key Encryption key, also required for decryption
 * @param string $raw Raw string to be encrypted
 *
 * @return string Raw data encrypted with key
 */
// function encrypt($key, $raw) {
// 	return base64_encode(mcrypt_encrypt(
// 			MCRYPT_RIJNDAEL_256,
// 			md5($key),
// 			$raw,
// 			MCRYPT_MODE_CBC,
// 			md5(md5($key))
// 	));
// }

/**
 * Decrypts an encrypted string
 *
 * Do not use this function, it is only here for historical reference
 *
 * @param string $key       Encryption key, also used during encryption
 * @param string $encrypted Encrypted string to be decrypted
 *
 * @return string Decrypted string or `null` if key/meta has been tampered with
 */
// function decrypt($key, $encrypted) {
// 	return rtrim(
// 		mcrypt_decrypt(
// 			MCRYPT_RIJNDAEL_256,
// 			md5($key),
// 			base64_decode($encrypted),
// 			MCRYPT_MODE_CBC,
// 			md5(md5($key))
// 		)
// 	);
// }

example.php

<?php

require 'encrypt-decrypt.php';

$key       = 'letmein';
$raw       = 'Lorem ipsum dolor sit amet, consectetur adipisicing elit.';
$meta      = [ 'name' => 'Rich', 'email' => 'rich@richjenks.com' ];
$encrypted = encrypt($key, $raw, $meta);
$decrypted = decrypt($key, $encrypted, $meta);

echo 'KEY:';
var_dump($key);
echo 'RAW:';
var_dump($raw);
echo 'META:';
var_dump($meta);
echo 'ENCRYPTED:';
var_dump($encrypted);
echo 'DENCRYPTED:';
var_dump($decrypted);

Not working. it showing a fatal error "Fatal error: Uncaught Error: Call to undefined function mcrypt_create_iv()". because this function has been deprecated from PHP version 7.

Hi there!

For any person that could be looking for crypting info please don't use this method. You should use OpenSSL instead https://www.php.net/manual/es/book.openssl.php

Best regards.