Secure Password Generator Tool

Improved prompt:

Design and implement a state-of-the-art secure password generator application using modern web technologies, focusing on cryptographic security, user experience, and functional breadth. Your task is to create a responsive and dynamic HTML5 interface, styled with clean and professional CSS3, driven by a robust and secure JavaScript engine.

Key requirements:

1. Password Generation Core: Build the core logic to generate passwords using a cryptographically secure random number generator (CSPRNG) compatible with Web Cryptography API or similar standards. Ensure the output passes NIST SP 800-90A tests for entropy and randomness.

2. User Interface: Develop an intuitive and interactive interface with real-time password preview. Use HTML5 elements (e.g., input fields, sliders, toggles) and CSS animations to provide immediate visual feedback. The interface should be both desktop and mobile-friendly.

3. Password Customization: Implement a password length customization feature with presets for different security levels (e.g., "Basic", "High", "Maximum"). Use JavaScript to validate and update the password strength dynamically as the user adjusts the length.

4. Character Type Toggles: Include independent toggles for including uppercase letters, lowercase letters, numeric digits, and special symbols. Use CSS colors or icons to visually indicate the current selection state of each toggle.

5. Password Strength Meter: Develop an advanced password strength meter that calculates entropy bits using the Shannon entropy formula or a similar standard. Additionally, estimate the theoretical time required to crack the password using a modern GPU cluster, displayed in hours or days.

6. Copy Functionality: Add a one-click "Copy Password" button that automatically selects the generated password, copies it to the clipboard, and displays a confirmation message. Implement automatic clipboard clearing after a short interval (e.g., 30 seconds) for security purposes.

7. Password Vault: Create a password vault feature that securely stores generated passwords in the browser's localStorage using the Web Cryptography API. Implement encryption and decryption functions to protect the data at rest.

8. Batch Generation: Extend the functionality to generate multiple passwords simultaneously with a batch option. Allow the user to specify the number of passwords to generate and offer options for different batch sizes (e.g., 5, 10, 20).

9. Password History: Maintain a password history log with a timestamp for each generated password. Display the history in a scrollable list or a separate tab, allowing the user to view and manage previously generated passwords.

10. Entropy Calculation: Implement the Shannon entropy formula or a similar standard to calculate the entropy of generated passwords. Display the result in bits, along with a visual indicator of the entropy level (e.g., a color-coded bar).

11. Memorable Passwords: Offer additional generation options for memorable passwords, such as phrase-based (e.g., random sentences) or pattern-based (e.g., "1qaz2wsx" style).

12. Export Functionality: Develop an export feature that allows the user to save generated passwords to a file (e.g., JSON or CSV) with encryption options (e.g., AES-256 or other industry-standard algorithms).

Throughout the development, ensure the application adheres to best practices for web security, including proper input validation, output encoding, and error handling. The final product should be both secure and user-friendly, providing a comprehensive password management solution.