2

With no server and only in the browser I'm generating an a bip39 key and giving the user the mnemonic to store some place safe for restoring, I also want the user to be able to login with a password.

1) Could I encrypt the mnemonic with a password?

2) If I do encrypt the mnemonic, which algorithm should I use?

2

Bip39 has an optional "encryption" over PBKDF2 (passphrase-to-key) used as salt (this allows possible deniability). https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#from-mnemonic-to-seed

The weakness there is that BIP39 uses only 2048 rounds during KDF. Which is easy to bruteforce.

If you store it in a cloud (or similar), I recommend to do a AES-256-CBC encryption of the mnemonic with a strong password and a strong KDF (maybe use PBKDF2 with at least 30'000 rounds).

  • Jonas, thank you for your reply. Please can you help me understand the benefits of AES-256-CBC over AES-256-GCM? Specifically in relation to encrypting a mnemonic in the browser – Will-In-China Apr 10 '17 at 11:55
  • 1
    That's a difficult question with probably multiple answers. GCM has serval advantages (HMAC) and some disadvantages (small IV) over CBC. It depends on your use-case. For purely disk encryption, CBC seems to be the most common choice. – Jonas Schnelli Apr 10 '17 at 12:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.