Subject: [Cfrg] [Errata Verified] RFC7748 (4730)

From: RFC Errata System <[email-masked]>
Date: Tue, 5 Jul 2016 12:19:10 -0700 (PDT)

The following errata report has been verified for RFC7748,
"Elliptic Curves for Security". 

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=7748&eid=4730

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Status: Verified
Type: Technical

Reported by: Adam Langley <[email-masked]>
Date Reported: 2016-07-05
Verified by: Lars Eggert (IRSG)

Section: 4.1

Original Text
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V(P)  147816194475895447910205935684099868872646061346164752889648818
37755586237401

Corrected Text
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V(P)  431144251710685529207648989359339670393703861982038067307639101
66200978582548

Notes
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The Montgomery form of the curve is generally used with a ladder, where the v coordinate is unused and unspecified. Thus I picked the smaller of the two possible values for v.

However, the curve is birationally equivalent to edwards25519, where both coordinates of the base point are used and are already in widespread use. Sadly, picking the smaller of the values for v ends up mapping to the negative of the base point on edwards25519.

This change replaces v with -v so that it matches up.

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RFC7748 (draft-irtf-cfrg-curves-11)
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Title               : Elliptic Curves for Security
Publication Date    : January 2016
Author(s)           : A. Langley, M. Hamburg, S. Turner
Category            : INFORMATIONAL
Source              : Crypto Forum Research Group
Area                : N/A
Stream              : IRTF
Verifying Party     : IRSG