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Could anyone explain me the difference between "key_share" extension and "server_key_exchange" message in TLS (1.3) ? If I understood right, these "packets" of data are used to send a key material to generate premaster keys. But what's the difference ? In which case a server must use one or another

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Could anyone explain me the difference between "key_share" extension and "server_key_exchange" message in TLS (1.3) ?

server_key_exchange isn't used in TLS 1.3. It was used in TLS 1.2; however when they modified the protocol to go to TLS 1.3, they opted not use it. However, they wanted to keep the same handshake types (many of the types are applicable to both 1.2 and 1.3; I suppose it made implementing software that supported both versions of the protocol a bit easier), and so they kept that value (12) as reserved.

Instead, in TLS 1.3, both the client and the server use the key_share extension.

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  • $\begingroup$ thank you very much! $\endgroup$
    – LUN
    Commented May 4, 2023 at 21:33
  • $\begingroup$ @LUN: if you like the answer, accept it and upvote it $\endgroup$
    – poncho
    Commented May 4, 2023 at 22:29
  • $\begingroup$ OK, I have done it. $\endgroup$
    – LUN
    Commented May 9, 2023 at 17:53

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