Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Consensus and a way forward]
Ilari Liusvaara <ilari.liusvaara@elisanet.fi> Mon, 01 December 2014 17:53 UTC
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Date: Mon, 01 Dec 2014 19:53:44 +0200
From: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
To: Adam Langley <agl@imperialviolet.org>
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Subject: Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Consensus and a way forward]
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On Mon, Dec 01, 2014 at 06:17:07AM -0800, Adam Langley wrote: > On Sun, Nov 30, 2014 at 7:33 PM, Robert Ransom <rransom.8774@gmail.com> wrote: > > > Interesting suggestion. > > > > Both 89747 and 121665 are 17 bits long (they are between 2^17 and 2^18 > > - 1), and 89747 has a slightly greater Hamming weight than 121665 (10 > > rather than 9); I would expect any performance improvement on due to > > that change in curve parameter to be quite small and only applicable > > to a very few implementation strategies. Have you done any > > benchmarking to quantify the performance improvement that you are > > claiming as a technical benefit of PinkBikeShed? > > I've not done any benchmarking, it's just a guess. But the Edward's d > parameter for the curve isomorphic to Curve25519 isn't 121665, it's > +/- 121665/121666 [http://eprint.iacr.org/2007/286.pdf, section 2]. > That value doesn't have a small representation so I think that the > PinkBikeShed curve does get to use a multiplication by a small > constant in place of a multiplication by a large constant. That might > be a small help. The isogeny that lets one in effect have small d and a24 at the same time also exists for Curve25519. AFAICT: Complete Twisted Edwards curve: -x^2+y^2=1+121665x^2*y^2 (mod 2^255-19) With base point: x=8343919484931660353238246604028044872330114539683257561218125599081866236258 y=10591048728587107161910258178281284043396286849160988064050992288107790236293 Mapped by: u = -y^2/x^2 v = y*(-x^2+y^2-2)/(i*x^3) Where (square root of -1): i=38214883241950591754978413199355411911188925816896391856984770930832735035197 Maps to complete Montgomery curve: v^2 = u^3 + 486662 * u^2 + u (mod 2^255-19) With base point: u=9 v=14781619447589544791020593568409986887264606134616475288964881837755586237401 Mapped by: w=u+19298681539552699237261830834781317975544997444273427339909597334652188435537 Maps to Weierstrass curve v^2=w^3+a*w+b: a=19298681539552699237261830834781317975544997444273427339909597334573241639236 b=55751746669818908907645289078257140818241103727901012315294400837956729358436 With base point: w=19298681539552699237261830834781317975544997444273427339909597334652188435546 v=14781619447589544791020593568409986887264606134616475288964881837755586237401 All the curves have base order of: 7237005577332262213973186563042994240857116359379907606001950938285454250989 The middle curve and base point match Curve25519 data from Safecurves after changing variable names (x,y)->(u,v). The v(x,y) formula looks messy, but for single-coordinate Montgomery, one only needs u(x,y), which is reasonably fast. And looks like one can compute v(x,y) together with u(x,y) pretty cheaply (few extra multiplications and additions). The reverse maps x(u,v) and y(u,v) are more annoying, seemingly containing two square roots and an inversion (among with few other ops). -Ilari
- [Cfrg] Consensus and a way forward Benjamin Black
- Re: [Cfrg] Consensus and a way forward Watson Ladd
- Re: [Cfrg] Consensus and a way forward Joppe Bos
- Re: [Cfrg] Consensus and a way forward Hannes Tschofenig
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] Consensus and a way forward Ilari Liusvaara
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Adam Langley
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Mike Hamburg
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] Consensus and a way forward Paterson, Kenny
- Re: [Cfrg] Consensus and a way forward Paterson, Kenny
- Re: [Cfrg] Consensus and a way forward Paterson, Kenny
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alexey Melnikov
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Michael Hamburg
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Robert Ransom
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Adam Langley
- Re: [Cfrg] Consensus and a way forward Lochter, Manfred
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Ilari Liusvaara
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Robert Ransom
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Watson Ladd
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Tony Arcieri
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… D. J. Bernstein
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Robert Ransom
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Watson Ladd
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paterson, Kenny
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alyssa Rowan
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Watson Ladd
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Benjamin Black
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Robert Ransom
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paul Hoffman
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alexey Melnikov
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paterson, Kenny
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Alexey Melnikov
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Watson Ladd
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paterson, Kenny
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Harry Halpin
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paul Hoffman
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Watson Ladd
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Tanja Lange
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Salz, Rich
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Tony Arcieri
- Re: [Cfrg] Mishandling twist attacks D. J. Bernstein
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Paterson, Kenny
- Re: [Cfrg] draft-black-rpgecc-00-.txt [was: Conse… Tanja Lange
- Re: [Cfrg] Mishandling twist attacks Paterson, Kenny
- Re: [Cfrg] Mishandling twist attacks D. J. Bernstein
- Re: [Cfrg] Mishandling twist attacks Salz, Rich
- Re: [Cfrg] Mishandling twist attacks Stephen Farrell
- Re: [Cfrg] Mishandling twist attacks Adam Back