Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1Ws09q-0001xq-MM for bitcoin-development@lists.sourceforge.net; Wed, 04 Jun 2014 01:38:26 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.192.42 as permitted sender) client-ip=209.85.192.42; envelope-from=cshrem@gmail.com; helo=mail-qg0-f42.google.com; Received: from mail-qg0-f42.google.com ([209.85.192.42]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1Ws09p-0000vO-3y for bitcoin-development@lists.sourceforge.net; Wed, 04 Jun 2014 01:38:26 +0000 Received: by mail-qg0-f42.google.com with SMTP id q107so14847390qgd.29 for ; Tue, 03 Jun 2014 18:38:19 -0700 (PDT) X-Received: by 10.224.4.66 with SMTP id 2mr988789qaq.58.1401845899279; Tue, 03 Jun 2014 18:38:19 -0700 (PDT) MIME-Version: 1.0 Received: by 10.96.52.106 with HTTP; Tue, 3 Jun 2014 18:38:04 -0700 (PDT) In-Reply-To: <87iooi40ws.fsf@rustcorp.com.au> References: <2341954.NpNStk60qp@1337h4x0r> <201406030452.40520.luke@dashjr.org> <87iooi40ws.fsf@rustcorp.com.au> From: "Charlie 'Charles' Shrem" Date: Tue, 3 Jun 2014 21:38:04 -0400 Message-ID: To: Rusty Russell Content-Type: multipart/alternative; boundary=001a11c2e886db5d9c04faf8ae1d X-Spam-Score: -0.6 (/) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (cshrem[at]gmail.com) -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [209.85.192.42 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 1.0 HTML_MESSAGE BODY: HTML included in message -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1Ws09p-0000vO-3y Cc: "bitcoin-development@lists.sourceforge.net" Subject: Re: [Bitcoin-development] Lets discuss what to do if SHA256d is actually broken X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 04 Jun 2014 01:38:26 -0000 --001a11c2e886db5d9c04faf8ae1d Content-Type: text/plain; charset=ISO-8859-1 Hey Rusty, This is intriguing, do you have a writeup somewhere I can read more about ? Thanks, Charlie CharlieShrem.com | *Please **encrypt messages with my PGP key * On Tue, Jun 3, 2014 at 8:45 AM, Rusty Russell wrote: > Luke Dashjr writes: > > On Tuesday, June 03, 2014 4:29:55 AM xor wrote: > >> Hi, > >> > >> I thought a lot about the worst case scenario of SHA256d being broken > in a > >> way which could be abused to > >> A) reduce the work of mining a block by some significant amount > >> B) reduce the work of mining a block to zero, i.e. allow instant mining. > > > > C) fabricate past blocks entirely. > > > > If SHA256d is broken, Bitcoin as it is fails entirely. > > I normally just lurk, but I looked at this issue last year, so thought > I'd chime in. I never finished my paper though... > > In the event of an *anticipated* weakening of SHA256, a gradual > transition is possible which avoids massive financial disruption. > > My scheme used a similar solve-SHA256-then-solve-SHA3 (requiring an > extra nonce for the SHA3), with the difficulty of SHA256 ramping down > and SHA3 ramping up over the transition (eg for a 1 year transition, > start with 25/26 SHA2 and 1/26 SHA3). > > The hard part is to estimate what the SHA3 difficulty should be over > time. My solution was to adjust only the SHA3 target on every *second* > difficulty change (otherwise assume that SHA2 and SHA3 have equally > changed rate and adjust targets on both). > > This works reasonably well even if the initial SHA3 difficulty is way > off, and also if SHA2 breaks completely halfway through the transition. > > I can provide more details if anyone is interested. > > Cheers, > Rusty. > > > ------------------------------------------------------------------------------ > Learn Graph Databases - Download FREE O'Reilly Book > "Graph Databases" is the definitive new guide to graph databases and their > applications. Written by three acclaimed leaders in the field, > this first edition is now available. Download your free book today! > http://p.sf.net/sfu/NeoTech > _______________________________________________ > Bitcoin-development mailing list > Bitcoin-development@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/bitcoin-development > --001a11c2e886db5d9c04faf8ae1d Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Hey Rusty,=A0

This is intriguing, do you have = a writeup somewhere I can read more about ?=A0

Thanks,=A0

Charl= ie
= CharlieShrem.com |=A0Please=A0encrypt messages with=A0my PGP key


On Tue, Jun 3, 2014 at 8:45 AM, Rusty Ru= ssell <rusty@rustcorp.com.au> wrote:
Luke Dashjr <luke@dashjr.org> = writes:
> On Tuesday, June 03, 2014 4:29:55 AM xor wrote:
>> Hi,
>>
>> I thought a lot about the worst case scenario of SHA256d being bro= ken in a
>> way which could be abused to
>> A) reduce the work of mining a block by some significant amount >> B) reduce the work of mining a block to zero, i.e. allow instant m= ining.
>
> C) fabricate past blocks entirely.
>
> If SHA256d is broken, Bitcoin as it is fails entirely.

I normally just lurk, but I looked at this issue last year, so thought
I'd chime in. =A0I never finished my paper though...

In the event of an *anticipated* weakening of SHA256, a gradual
transition is possible which avoids massive financial disruption.

My scheme used a similar solve-SHA256-then-solve-SHA3 (requiring an
extra nonce for the SHA3), with the difficulty of SHA256 ramping down
and SHA3 ramping up over the transition (eg for a 1 year transition,
start with 25/26 SHA2 and 1/26 SHA3).

The hard part is to estimate what the SHA3 difficulty should be over
time. =A0My solution was to adjust only the SHA3 target on every *second* difficulty change (otherwise assume that SHA2 and SHA3 have equally
changed rate and adjust targets on both).

This works reasonably well even if the initial SHA3 difficulty is way
off, and also if SHA2 breaks completely halfway through the transition.

I can provide more details if anyone is interested.

Cheers,
Rusty.

---------------------------------------------------------------------------= ---
Learn Graph Databases - Download FREE O'Reilly Book
"Graph Databases" is the definitive new guide to graph databases = and their
applications. Written by three acclaimed leaders in the field,
this first edition is now available. Download your free book today!
http://p.sf.net/s= fu/NeoTech
_______________________________________________
Bitcoin-development mailing list
Bitcoin-develo= pment@lists.sourceforge.net
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