How do you encrypt local storage data in HTML5?

2 CryptoJS library

CryptoJS is a popular JavaScript library that implements various cryptographic algorithms and utilities. It is compatible with the Web Crypto API and can be used to encrypt and decrypt data using different modes and padding schemes. You can use CryptoJS to convert data between different formats, such as strings, hex, base64, and words. To use CryptoJS, you need to include the library in your HTML file or import it as a module in your JavaScript file.

3 Encrypting local storage data

To encrypt local storage data in HTML5, you need to generate a random key using the Web Crypto API's crypto.subtle.generateKey method and export it as a raw format. Convert the key to a base64 string with CryptoJS.enc.Base64.stringify and store it in local storage with the localStorage.setItem method. Then, use the CryptoJS.AES.encrypt method to encrypt the data, specifying the mode, padding, and initialization vector (IV) for the encryption in an optional configuration object. Finally, convert the cipher text object to a string with the toString method and store it in local storage with localStorage.setItem.

4 Decrypting local storage data

To decrypt local storage data in HTML5, you must first retrieve the key from the local storage using the localStorage.getItem method, which you can use with the same name that you used to store the key. Then, convert the key from a base64 string to an ArrayBuffer via CryptoJS.enc.Base64.parse method, which decodes the key data. After that, import the key as a raw format using crypto.subtle.importKey method to return a key object that matches the algorithm and usage that you used to generate the key. Next, retrieve the encrypted data from local storage using localStorage.getItem method, again using the same name that you used to store it. Convert this encrypted data from a string to a cipher text object using CryptoJS.AES.decrypt method with data, key, and an optional configuration object as arguments for specifying mode, padding, and IV for decryption. This will return a plain text object containing decrypted data and IV. Finally, convert this plain text object to a string with the toString method to decode plain text and IV as UTF-8 string, before using the decrypted data as needed in your application.

5 Encrypting cookies

To encrypt cookies in HTML5, you can use a similar approach as encrypting local storage data. However, instead of storing the key and the encrypted data in the local storage, you need to store them as cookies using the document.cookie property. You also need to specify some attributes for the cookies, such as the name, value, expiration date, path, domain, and secure flag. To encrypt and decrypt cookies, you can use the same methods from the Web Crypto API and the CryptoJS library as described above.