Subject: [Bitcoin-development] String-based Hierarchical Deterministic Keys - Alternative to BIP 32

From: Mike Koss <[email-masked]>
Date: Tue, 4 Dec 2012 19:06:00 -0800

I've implemented an alternative to the BIP 32 proposal.  I wanted a system
based on a hierarchical string representation (rather than hierarchy of
integers as BIP 32 proposes).  For example I name keys like this:

[hd1.75491111].store.1. 1D7GM5dkUtxvGeWgn7SYtanBuyj1MD1EZy
[hd1.75491111].store.2. 1QAqDbzpNKViGSjVe1XmnGbmZtvz5hM7t1
[hd1.75491111].store.3. 14XkSN92QLGeorYPpoVbG87DQhowEx3mFn
[hd1.75491111].store.4. 1JLcGdod6Wm33rMZuZZUmAEE6osLhM4QMn

First draft of proposal:

https://gist.github.com/4211704

I envision using this in services, so I've not done any work to recommend
how the keys would be represented directly in the client (I just map from a
seed value and
a hierarchy string in order to deterministic ally derive ECDSA public and
private keys).

I'm happy to release my source code for this (Python).  But I'd first like
to get feedback about any security concerns with my scheme (I note that I
don't introduce the enlarged
key space that BIP 32 does with its "chain code" - I'm wondering if that
represents a weakness of my scheme vs. BIP 32).

On Mon, Dec 3, 2012 at 12:44 PM, Pieter Wuille <[email-masked]>wrote:

> On Mon, Dec 03, 2012 at 06:48:34AM -0800, Amir Taaki wrote:
> > ok, also what is the reasoning behind serialising points using a
> compressed
> > format before going into the hash function? I'm looking at the
> sec1-v2.pdf
> > and the compression format is a little confusing.
>
> I don't think there is a compelling reason to encourage uncompressed public
> keys anymore on the network. They take more space in the block chain for no
> additional value whatsoever. Software may of course continue supporting
> uncompressed keys if they wish to provide compatibility, but for a new
> standard, I think it makes sense to standardize on just compressed keys.
> And since that software thus needs to support the compressed encoding,
> there is no reason to use a different encoding inside the derivation scheme
> itself.
>
> Regarding the encoding itself, it is not hard: just 0x02 or 0x03 (depending
> on whether Y is even or odd) followed by the 32-byte encoding of X.
> Decoding
> is harder, but is never needed in the derivation. Software internally can
> use
> any representation (and it will), which in almost all circumstances stores
> both X and Y (and even more). Decoding compressed public keys is somewhat
> harder, as Y must be reconstructed (but the algorithm isn't hard) - this is
> only necessary when someone wants to import an extended public key though
> for
> watch-only wallets.
>
> --
> Pieter
>
>
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-- 
Mike Koss
CTO, CoinLab
(425) 246-7701 (m)

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