safercrypto.php

<?php
    class SaferCrypto extends UnsafeCrypto {
        const HASH_ALGO = 'sha256';
        
        public static function encrypt($message, $key, $encode = false) {
            list($encKey, $authKey) = self::splitKeys($key);
            $ciphertext = parent::encrypt($message, $encKey);
            $mac = hash_hmac(self::HASH_ALGO, $ciphertext, $authKey, true);
    
            if ($encode) {
                return base64_encode($mac.$ciphertext);
            }
            
            return $mac.$ciphertext;
        }
        
        public static function decrypt($message, $key, $encoded = false) {
            list($encKey, $authKey) = self::splitKeys($key);
            if ($encoded) {
                $message = base64_decode($message, true);
                if ($message === false) {
                    throw new Exception('Encryption failure');
                }
            }
            
            $hs = mb_strlen(hash(self::HASH_ALGO, '', true), '8bit');
            $mac = mb_substr($message, 0, $hs, '8bit');
    
            $ciphertext = mb_substr($message, $hs, null, '8bit');
    
            $calculated = hash_hmac(
                self::HASH_ALGO,
                $ciphertext,
                $authKey,
                true
            );
    
            if (!self::hashEquals($mac, $calculated)) {
                throw new Exception('Encryption failure');
            }
            
            $plaintext = parent::decrypt($ciphertext, $encKey);
            return $plaintext;
        }
    
        protected static function splitKeys($masterKey) {
            return [
                hash_hmac(self::HASH_ALGO, 'ENCRYPTION', $masterKey, true),
                hash_hmac(self::HASH_ALGO, 'AUTHENTICATION', $masterKey, true)
            ];
        }
        
        protected static function hashEquals($a, $b) {
            if (function_exists('hash_equals')) {
                return hash_equals($a, $b);
            }
            $nonce = openssl_random_pseudo_bytes(32);
            return hash_hmac(self::HASH_ALGO, $a, $nonce) === hash_hmac(self::HASH_ALGO, $b, $nonce);
        }
    }
?>