It's not quite enough to just do SHA512, you missed out this condition (incredibly rare as it is):

> In case IL is 0 or ≥n, the master key is invalid.

Also I can't see how I would use this to seed a hardware wallet that requires a BIP39 seed as mentioned in your abstract.

For both of those reasons, you may want to just invent/formalize a scheme that takes Cards -> Entropy.

From that Entropy one can generate BIP39, and non-BIP39 fans can just continue, generate and store their root xprv.

Prior art: Note that Ian Coleman's BIP39 site already supports Cards (and Dice), see the logic here: https://github.com/iancoleman/bip39/blob/master/src/js/entropy.js

Note it detected "full deck". It also calculates the Total Bits of Entropy and can handle card replacement and multiple decks.

PS, you're a bit out on your entropy calculation, log2(52!) ~= 225.58 bits, not 219.

On Tue, 5 Feb 2019 at 02:08, Devrandom via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

I would suggest 50+ 6-sided dice rolls, giving about 128 bits of entropy.  Compared to a shuffle, it's easier to be sure that you got the right amount of entropy, even if the dice are somewhat biased.

On Mon, Feb 4, 2019 at 2:33 PM James MacWhyte via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

James

On Sun, Feb 3, 2019 at 10:27 AM Ryan Havar via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

Conveniently a shuffled deck of cards also can serve as a physical backup which is easy to hide in plain sight with great plausible deniability.

To make sure someone doesn't play with your cards and mix up the order, use a permanent marker to draw a diagonal line on the side of the deck from corner to corner. If the cards ever get mixed up, you can put them back in order by making sure the diagonal line matches up. 

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