public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: "Russell O'Connor" <roconnor@blockstream.io>
To: Peter Todd <pete@petertodd.org>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Fast Merkle Trees
Date: Thu, 7 Sep 2017 11:51:14 -0400	[thread overview]
Message-ID: <CAMZUoKk=00AJbtq602P=MWtGhWUY_7oCrWEUj+K7xp_+DOOTYg@mail.gmail.com> (raw)
In-Reply-To: <20170907055557.GA12638@fedora-23-dvm>

[-- Attachment #1: Type: text/plain, Size: 1138 bytes --]

On Thu, Sep 7, 2017 at 1:55 AM, Peter Todd <pete@petertodd.org> wrote:

> On Wed, Sep 06, 2017 at 09:59:54PM -0400, Russell O'Connor via bitcoin-dev
> wrote:
> > The fast hash for internal nodes needs to use an IV that is not the
> > standard SHA-256 IV. Instead needs to use some other fixed value, which
> > should itself be the SHA-256 hash of some fixed string (e.g. the string
> > "BIP ???" or "Fash SHA-256").
>
> Note that in general, designs should *not* create new hash functions by
> using
> custom IVs, but rather use bog-standard SHA256, and make a fixed first
> block.
> That allows unoptimised implementations to just hash a block with the
> second
> initialization value, and optimized implementations to start with the fixed
> midstate.


I 100% agree.

With SHA256 every final state is also a valid midstate.  Therefore, using a
custom IV of the SHA256 hash of some fixed string results in a hash of data
that is functionally equivalent to prefixing the data with the padded
version of the fixed string and using a regular SHA256 hash of the combined
data.  This is important and I should have explicitly pointed it out.

[-- Attachment #2: Type: text/html, Size: 1564 bytes --]

      reply	other threads:[~2017-09-07 15:51 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-07  1:59 [bitcoin-dev] Fast Merkle Trees Russell O'Connor
2017-09-07  2:20 ` Mark Friedenbach
2017-09-07 15:43   ` Russell O'Connor
2017-09-07 17:42     ` Mark Friedenbach
2017-09-07 18:55       ` Russell O'Connor
2017-09-07 20:04         ` Mark Friedenbach
2017-09-12 11:44           ` Johnson Lau
2017-09-07  5:55 ` Peter Todd
2017-09-07 15:51   ` Russell O'Connor [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAMZUoKk=00AJbtq602P=MWtGhWUY_7oCrWEUj+K7xp_+DOOTYg@mail.gmail.com' \
    --to=roconnor@blockstream.io \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    --cc=pete@petertodd.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox