is it possible to use (bip39) 12 words passphrase in yoroi?

Question

Currently I have a 12 words passphrase that I use over some wallets like exodus and metamask, I want to use the same 12 words on yoroi but yoroi only allows me to use 15 or 24 words.

• I was under the impression that yoroi uses bip39 standard, why I can't create a wallet with only 12 words?
• What is the technical limitation that prevents yoroi to use 12?
• Is there an existing way (without coding it myself) to transform my 12 words into 15?, or 24?, assuming that 12 word passphrases are just 12*11=132 bits of entropy (128 bit entropy + 4 bit checksum) [reference here]

I want to avoid creating a new wallet entirely and now having to backup 12+24=36 words for reasons out of this scope.

(like for example I already etched the 12 words in metal using carbon atoms and I don't want to do it again because is expensive).

Answer 1

Yoroi dev here.

Yoroi uses 15 words because we think it's the best trade-off between security and convenience. Using more words may provide marginal security benefits, but you also have downsides like more difficulty if you want to memorise your mnemonics, more risk of writing down the wrong word or in the wrong order during backups, more inconvenience using offline metal backup devices (because you need to backup more words) and so on.

We also allow to recover 24-word mnemonics so that Daedalus users can use Yoroi if they want to. But allowing for more options compromises usability/UX. It's not a technical choice.

I don't see why you could not "stretch" a 12-word recovery phrase to obtain 15 words. You just need to make sure that the checksum is valid.

Finally, and more importantly, I am not sure that trying to use the same recovery phrase to manage multiple wallets is a good practice (hardware wallets are an exception of course). But ultimately, it's your choice.

Answer 2

After reading the bip39 specification, I learned that a 12 word mnemonic phrase was generated using an entropy of 128 bits, if I want to use a 24 word passphrase, there shall be no way to generate it from a 12 word list the entropy for a 24 word mnemonic phrase uses a 256 bit entropy + 8 bits of checksum which finally generates a 256 + 8 = 264 bits of random bits that can be split on 24 words of 11 bits, thus using the 2048 (2^11) words in the bip39 word list.

I wonder if I can use a key stretching algorithm like PBKDF2+HMAC-SHA512 algorithms, to produce a 256-bit (or it's first 256 bits) values as its final output in order to generate the 24 words mnemonic phrase I want, from only a list of 12 words, but I am not sure about how secure this is (well, of course is less secure because I cut the search space in half).

For now, I think the most secure way to obtain a 24 words mnemonic passphrase is to just create a new wallet on yoroi and just manage 2 mnemonic phrases, one with 12 words for btc and other altcoins (via trezor wallet and exodus), and a 24 word mnemonic phrase for cardano using yoroi :c

I leave this answer for any future reader, please let me know if I am wrong, please have a good day.