浏览器文件加密工具

请使用 HTML5、CSS3 和 JavaScript，结合 Web Crypto API，创建一个客户端文件加密工具。构建支持拖放的文件选择界面，并显示进度指示器。实现 AES-256-GCM 加密，并通过 PBKDF2 从密码进行安全的密钥派生。支持同时批量加密多个文件。加入密码强度校验，并计算熵值。生成可下载的加密文件，并支持自定义文件扩展名。创建带有密码验证功能的解密界面。实现安全的内存处理，自动清除敏感数据。添加加密操作的详细日志，且不存储敏感信息。支持加密密钥的导出与导入，并附带明确的安全警告。使用流式加密和分块处理来支持大文件。

Create a client-side file encryption tool using HTML5, CSS3, and JavaScript with the Web Crypto API. Build a drag-and-drop interface for file selection with progress indicators. Implement AES-256-GCM encryption with secure key derivation from passwords (PBKDF2). Add support for encrypting multiple files simultaneously with batch processing. Include password strength enforcement with entropy calculation. Generate downloadable encrypted files with custom file extension. Create a decryption interface with password verification. Implement secure memory handling with automatic clearing of sensitive data. Add detailed logs of encryption operations without storing sensitive information. Include export/import of encryption keys with proper security warnings. Support for large files using streaming encryption and chunked processing.