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Forbid key share reuse #1410

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Forbid key share reuse #1410

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1e5ab62
Renamed
ekr Dec 17, 2025
b749243
Forbid key reuse
ekr Mar 16, 2026
a505cd1
Update changelog
ekr Mar 16, 2026
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11 changes: 7 additions & 4 deletions draft-ietf-tls-rfc8446bis.md → rfc9846.md
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Expand Up @@ -546,6 +546,8 @@ editorial improvements. In addition, it removes the use of the term
names where no term was necessary. This document makes the following
specific technical changes:

- Forbid the reuse of KeyShare values between connections.

- Forbid negotiating TLS 1.0 and 1.1 as they are now deprecated by {{!RFC8996}}.

- Removes ambiguity around which hash is used with PreSharedKeys and
Expand Down Expand Up @@ -2366,6 +2368,11 @@ KeyShareEntry values for groups not listed in the client's
these rules and abort the handshake with an "illegal_parameter" alert
if one is violated.

Clients and Servers MUST NOT reuse a key share for multiple
connections. Because {{RFC8446}} permitted reuse, receiving
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@muhammad-usama-sardar muhammad-usama-sardar Mar 16, 2026

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What exactly do you mean by receiving implementations?

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@ekr ekr Mar 16, 2026

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Implementations that receive key shares. I believe this to be adequately clear.

implementations MUST permit reuse by the peer in order to prevent
interoperability issues.

In a HelloRetryRequest message, the "extension_data" field of this
extension contains a KeyShareHelloRetryRequest value:

Expand Down Expand Up @@ -5391,10 +5398,6 @@ applications SHOULD NOT offer tickets across connections that are meant to be
uncorrelated. For example, {{FETCH}} defines network partition keys to separate
cache lookups in web browsers.

Clients and Servers SHOULD NOT reuse a key share for multiple connections. Reuse
of a key share allows passive observers to correlate different connections. Reuse
of a client key share to the same server additionally allows the server to correlate different connections.

It is RECOMMENDED that the labels for external identities be selected so that they
do not provide additional information about the identity of the
user. For instance, if the label includes an e-mail address, then
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