Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 8EF84267 for ; Sun, 8 May 2016 13:48:58 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-yw0-f176.google.com (mail-yw0-f176.google.com [209.85.161.176]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 8F8AD174 for ; Sun, 8 May 2016 13:48:57 +0000 (UTC) Received: by mail-yw0-f176.google.com with SMTP id j74so229556656ywg.1 for ; Sun, 08 May 2016 06:48:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=palatinus-cz.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to; bh=GY1IUQuxspTHukLmFvGHiicwc2rKBL3ATtfUSF7W1A0=; b=tnCNn5sXMYxNIAREvDKrfOPYoO5FvbiGh8WdsZZ84WNGI2+F3nuDq8OfUWi7Em/u6/ Quk9xzKXWKj1zjEx0W0r/YZwDVTQTAaSr/I0OXrT2zg0xsRyG8C1GDQIov0kRyQAxqCT 0UuTB3GiGUI8UdEFKJHy+6iKrKstXDPKetWExNbBb5zmACklHmXmy+7zTw6o6j0eX62K iyOTSqK67O0YjKanz6F/JrXTVrJGImdwEVebJ7tk1HwaokAXV9f0nx56PQmJnPLDDfHg D88xx2/ZfnzAH87Ii6mjtqRu4QRYAgXzQ+wXG2SdbRscZHGd21Ij0djm9ztLn22Nwmat EekQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to; bh=GY1IUQuxspTHukLmFvGHiicwc2rKBL3ATtfUSF7W1A0=; b=LYxXJKWDHdET0Jt7qs4IsL5Ayb9gIUHYOW0bcqeJSUYwj6dz3KMyCtkotBRFhdVMuX JiMXPGXeTQKo3jEZhm+d1f9x14B3tB6EdvptdRkUryLt9hfcdG7dYFfn6vycMzJW546B SbANwvDbbPrscMSihUcUjHEGEasSKnQ2IVb7ll4487HyGJWKwSMeq5PNFyiYyQQeT/xV YbfxzZQO2Use8T5zrjQLAi8N5kkxX2T36jemTx9xjpCKyna5hl6SI8nbfvKtLPR3eyh4 o8wgWgzfh97RNjBGQBtexCoGCE31WysdVURsTk2zSIyoDkEkt/p0D/bH01z3Ejp2nUYF pkcg== X-Gm-Message-State: AOPr4FVyTGHhsqIbsxEdZQNJZLiFn/QIGWedZb++GXvzB9GNaOpVrWcvmdn6LcGsrOsC9p5eDR4Wx68zLN68jA== X-Received: by 10.129.84.193 with SMTP id i184mr20003684ywb.285.1462715336526; Sun, 08 May 2016 06:48:56 -0700 (PDT) MIME-Version: 1.0 Received: by 10.129.92.2 with HTTP; Sun, 8 May 2016 06:48:27 -0700 (PDT) In-Reply-To: References: <5717AF19.1030102@gmail.com> From: Marek Palatinus Date: Sun, 8 May 2016 15:48:27 +0200 Message-ID: To: bitcoin-dev@lists.linuxfoundation.org Content-Type: multipart/alternative; boundary=001a114d9a500ac429053254f48d X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, HTML_MESSAGE, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Sun, 08 May 2016 14:16:09 +0000 Subject: [bitcoin-dev] Fwd: Proposal to update BIP-32 X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 08 May 2016 13:48:58 -0000 --001a114d9a500ac429053254f48d Content-Type: text/plain; charset=UTF-8 I received this: ---------- Forwarded message ---------- From: Pieter Wuille Date: Fri, Apr 22, 2016 at 6:44 PM Subject: Re: [bitcoin-dev] Proposal to update BIP-32 To: Marek Palatinus Cc: Bitcoin Dev On Thu, Apr 21, 2016 at 2:08 PM, Marek Palatinus wrote: > On Wed, Apr 20, 2016 at 6:32 PM, Jochen Hoenicke via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: > >> Hello Bitcoin Developers, >> >> I would like to make a proposal to update BIP-32 in a small way. >> >> I think the backward compatibility issues are minimal. The chance >> that this affects anyone is less than 10^-30. Even if it happens, it >> would only create some additional addresses (that are not seen if the >> user downgrades). The main reason for suggesting a change is that we >> want a similar method for different curves where a collision is much >> more likely. >> > I think I change like this makes a lot of sense technically, and I wish I had known how BIP-32 would end up being used inside higher level mechanisms that automatically increment the position beyond the control of the application generating them. The inclusion of the requirement was there because ECDSA is notorious for security problems under biased secret keys, though it's really only a certificational issue for secp256k1 (due to its group order being so close to 2^256). > >> #QUESTIONS: >> >> What is the procedure to update the BIP? Is it still possible to >> change the existing BIP-32 even though it is marked as final? Or >> should I make a new BIP for this that obsoletes BIP-32? >> > BIPs are not supposed to be updated with new ideas, only remarks/links/typos/clarifications/..., so that their bumbers can unambiguously be used to refer to an idea. My suggestion would be to write a new BIP that overrides parts of BIP32, and then put a note in BIP32 that a better mechanism is available that is unlikely to change things in reality for the secp256k1 curve. I guess > What algorithm is preferred? (bike-shedding) My suggestion: >> >> --- >> >> Change the last step of the private -> private derivation functions to: >> >> . In case parse(I_L) >= n or k_i = 0, the procedure is repeated >> at step 2 with >> I = HMAC-SHA512(Key = c_par, Data = 0x01 || I_R || ser32(i)) > > >> --- >> >> I think this suggestion is simple to implement (a bit harder to unit >> test) and the string to hash with HMAC-SHA512 always has the same >> length. I use I_R, since I_L is obviously not very random if I_L >= n. >> There is a minimal chance that it will lead to an infinite loop if I_R >> is the same in two consecutive iterations, but that has only a chance >> of 1 in 2^512 (if the algorithm is used for different curves that make >> I_L >= n more likely, the chance is still less than 1 in 2^256). In >> theory, this loop can be avoided by incrementing i in every iteration, >> but this would make an implementation error in the "hard to test" path >> of the program more likely. >> > The chance for failure is a bit higher than that, as it only requires a failed key (one in 2^128) in the first step, followed by an iteration that results in the same I_R to cause a cycle. If you take multiple failures before the cycle starts into account, the combined chance for failure is p/(1-p)^2 / 2^256 (with p the chance for a random inadmissable key), which is not much better than 1 in 2^128 for high values of p. An alternative that always converges is to retry with an appended iteration count is possible: { I = HMAC-SHA512(Key = c_par, Data = 0x01 || || ser32(i)) for the first iteration I = HMAC-SHA512(Key = c_par, Data = 0x01 || || ser32(i) || ser32(j)) for iteration number j, with j > 0 } Cheers, -- Pieter --001a114d9a500ac429053254f48d Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I received this:

------= ---- Forwarded message ----------
From: Pi= eter Wuille <pieter.wuille@gmail.com>
Date: Fri, Apr 22, 2016 at = 6:44 PM
Subject: Re: [bitcoin-dev] Proposal to update BIP-32
To: Mare= k Palatinus <marek@palatinus.cz>
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>


On Thu, Apr 21, 2016 at 2:08 PM, Marek Palatinus= <marek@palatinus.cz> wrote:

#QUESTIONS:

What is the procedure to update the BIP?=C2=A0 Is it still possible to
change the existing BIP-32 even though it is marked as final?=C2=A0 Or
should I make a new BIP for this that obsoletes BIP-32?

BIPs are not suppose= d to be updated with new ideas, only remarks/links/typos/clarifications/...= , so that their bumbers can unambiguously be used to refer to an idea. My s= uggestion would be to write a new BIP that overrides parts of BIP32, and th= en put a note in BIP32 that a better mechanism is available that is unlikel= y to change things in reality for the secp256k1 curve.

I guess
=C2=A0
What algorithm is preferred? (bike-shedding)=C2=A0 My suggestion:

---

Change the last step of the private -> private derivation functions to:<= br>
=C2=A0. In case parse(I_L) >=3D n or k_i =3D 0, the procedure is repeate= d
=C2=A0 =C2=A0at step 2 with
=C2=A0 =C2=A0 I =3D HMAC-SHA512(Key =3D c_par, Data =3D 0x01 || I_R || ser3= 2(i))=C2=A0
<= div class=3D"gmail_quote">

---

I think this suggestion is simple to implement (a bit harder to unit
test) and the string to hash with HMAC-SHA512 always has the same
length.=C2=A0 I use I_R, since I_L is obviously not very random if I_L >= =3D n.
There is a minimal chance that it will lead to an infinite loop if I_R
is the same in two consecutive iterations, but that has only a chance
of 1 in 2^512 (if the algorithm is used for different curves that make
I_L >=3D n more likely, the chance is still less than 1 in 2^256).=C2=A0= In
theory, this loop can be avoided by incrementing i in every iteration,
but this would make an implementation error in the "hard to test"= path
of the program more likely.
=

The chance for failure is a bit higher than that= , as it only requires a failed key (one in 2^128) in the first step, follow= ed by an iteration that results in the same I_R to cause a cycle. If you ta= ke multiple failures before the cycle starts into account, the combined cha= nce for failure is p/(1-p)^2 / 2^256 (with p the chance for a random inadmi= ssable key), which is not much better than 1 in 2^128 for high values of p.=

An alternative that always converges is to retry with an= appended iteration count is possible:
{
=C2=A0 I =3D HMAC= -SHA512(Key =3D c_par, Data =3D 0x01 ||=C2=A0 || ser32(i)) for the first it= eration
=C2=A0 I =3D HMAC-SHA512(Key =3D c_par, Data =3D 0x01 ||=C2=A0 |= | ser32(i) || ser32(j)) for iteration number j, with j > 0
}

<= /div>
Cheers,

--
Pieter


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