!!! Overview
[{$pagename}] (or "key_share") is a [TLS extension] contains the endpoint's cryptographic parameters.

[Clients] [MAY] send an empty [client_shares] vector in order to request group selection from the [server] at the cost of an additional round trip.  (see Section 4.1.4)

%%prettify 
{{{
struct {
    NamedGroup group;
        opaque key_exchange<1..2^16-1>;
} KeyShareEntry;
}}} /%

group - The named group for the key being exchanged.  Finite Field [Diffie-Hellman] [DH] parameters are described in Section 4.2.7.1; [Elliptic Curve Diffie-Hellman Ephemeral] parameters are described in Section 4.2.7.2.

key_exchange - Key exchange information.  The contents of this field are determined by the specified group and its corresponding definition.

The "extension_data" field of this extension contains a "KeyShare" value:
%%prettify 
{{{
struct {
    select (Handshake.msg_type) {
        case client_hello:
            KeyShareEntry client_shares<0..2^16-1>;

        case hello_retry_request:
            NamedGroup selected_group;

        case server_hello:
            KeyShareEntry server_share;
    };
} KeyShare;
}}} /%
!! More Information
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