Subject: [TLS] [Technical Errata Reported] RFC8446 (5483)

From: RFC Errata System <[email-masked]>
Date: Mon, 27 Aug 2018 20:29:52 -0700 (PDT)

The following errata report has been submitted for RFC8446,
"The Transport Layer Security (TLS) Protocol Version 1.3".

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You may review the report below and at:
http://www.rfc-editor.org/errata/eid5483

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Type: Technical
Reported by: Patrick Kelsey <[email-masked]>

Section: 4.2.8.2

Original Text
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For X25519 and X448, the contents of the public value are the byte
string inputs and outputs of the corresponding functions defined in
[RFC7748]: 32 bytes for X25519 and 56 bytes for X448.

Corrected Text
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For X25519 and X448, the contents of the public value are the byte
string outputs of the corresponding functions defined in [RFC7748]: 32
bytes for X25519 and 56 bytes for X448.

Notes
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Per Section 7.4.2 of this RFC and Section 6 of RFC7748, the byte string inputs to the corresponding ECDH scalar multiplication function are the private key and the u-coordinate of the standard public base point, the former of which of course must not be transmitted and the latter of which is a known constant.

>From another perspective, including the byte string inputs in the contents of the public value would contradict the resulting content sizes given at the end of the cited paragraph as well as the statement in Section 7.4.2 that the public key put into the KeyShareEntry is the output of ECDH scalar multiplication function.

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RFC8446 (draft-ietf-tls-tls13-28)
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Title               : The Transport Layer Security (TLS) Protocol Version 1.3
Publication Date    : August 2018
Author(s)           : E. Rescorla
Category            : PROPOSED STANDARD
Source              : Transport Layer Security
Area                : Security
Stream              : IETF
Verifying Party     : IESG