I am trying to "invent" secure client-side authentication where all data are stored in browser encrypted and only accessible with the correct password. My question is, what is your opinion about my idea. If you think it is not secure or there is possible backdoor, let me know.

// INPUT:
- test string (hidden, random, random length)
- password
- password again
// THEN:
- hash test string with sha-512
- encrypt test string with password
- save hash of test string
// AUTH:
- decrypt test string
- hash decrypted string with sha-512
- compare hashes
- create password hash sha-512 (and delete password from memory, so you cannot get it somehow - possible hole here because hash is reversible with brute force)

// DATA PROCESSING
- encrypt/decrypt with password hash as secret (AES-256)

Thanks!

EDIT: Maybe some salt for test string would be nice