For your passwords we store, we use AES-256 encryption with CBC mode and PKCS5 padding from the CryptoJS module to encrypt your passwords. Those encrypted passwords are stored in local storage and can be imported and exported from the settings panel. Your passwords are never send over the internet.
Your passwords are stored in the following way:
AES(paddingLength + paddTo256Multiple({domain, password, username}))
Where paddingLength always is 3 bytes telling how many padding bytes where added to your data. And paddTo256Multiple adds random bytes until your data is 256 bits long.