Re: [CFRG] Small subgroup question for draft-irtf-cfrg-hash-to-curve

"Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com> Fri, 09 April 2021 18:17 UTC

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From: "Scott Fluhrer (sfluhrer)" <sfluhrer@cisco.com>
To: Mike Hamburg <mike@shiftleft.org>, "Hao, Feng" <Feng.Hao@warwick.ac.uk>
CC: CFRG <cfrg@irtf.org>
Thread-Topic: [CFRG] Small subgroup question for draft-irtf-cfrg-hash-to-curve
Thread-Index: AQHXLUacM7sBZ3ZdE0a+hIjdr1H+CqqsQ0gAgAADtICAABZvgIAAC3EAgAATDWA=
Date: Fri, 9 Apr 2021 18:17:15 +0000
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References: <e270e62d-941d-0a87-7dc9-cf80f73b5aeb@jacaranda.org> <d0778523-5f5d-4327-b795-279918c1899c@www.fastmail.com> <CAMr0u6=PBX1W5zQFmpxKQ=ViUXN9QK00BREL4M0=2HOkaXaiZw@mail.gmail.com> <VI1SPR01MB03573585C37B871D200ECC23D6739@VI1SPR01MB0357.eurprd01.prod.exchangelabs.com> <4590aaa512acf5a482c9890ebe48f1760e5831a5.camel@loup-vaillant.fr> <F9593D27-3244-470E-89BE-85215B2DC9E7@shiftleft.org> <VI1SPR01MB0357AE729116A79C8DF70516D6739@VI1SPR01MB0357.eurprd01.prod.exchangelabs.com> <6F4F0566-3465-4C9C-8993-1B3FDFDDD792@shiftleft.org>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/cfrg/9awCqXWWSatiTeLE4x7sYfEccF0>
Subject: Re: [CFRG] Small subgroup question for draft-irtf-cfrg-hash-to-curve
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Opaque doesn’t use a hash-to-curve operation.

CPace does; it also automatically aborts (fails) if the hash-to-curve operation happens to return a low order point (that is, a point that, after multiplying by the cofactor, is the neutral element).

From: CFRG <cfrg-bounces@irtf.org> On Behalf Of Mike Hamburg
Sent: Friday, April 9, 2021 1:00 PM
To: Hao, Feng <Feng.Hao@warwick.ac.uk>
Cc: CFRG <cfrg@irtf.org>
Subject: Re: [CFRG] Small subgroup question for draft-irtf-cfrg-hash-to-curve

I don’t know if the same holds for OPAQUE or CPace: for all I know, they may have specification holes and/or end in failure in that case.