In TLS 1.3, and since the server signs the entire handshake messages including the server hello message, in this case, is the SNI extension of the client hello message, is it included in the content for which the signature is generated. I know that the cipher suites exchanged are signed, but not sure about the SNI.

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    $\begingroup$ In TLS (and not only TLS 1.3) the whole handshake (including ClientHello and thus also SNI) is integrity protected, i.e. protected against manipulation. Application data will only be sent once the integrity of the handshake is successfully verified when receiving the Finished message at the end of the handshake. $\endgroup$ Commented Sep 18, 2023 at 6:32
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    $\begingroup$ @SteffenUllrich: I think you can just put that in as an answer $\endgroup$
    – poncho
    Commented Sep 18, 2023 at 9:37


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