@Override
  public Bytes32 getNonce() {
    return nonce;
  }
The responder's handshake message.

<p>This message must be sent by the party who responded to the RLPX connection, in response to
the initiator message.

<h3>Message structure</h3>

The following describes the message structure:

<pre>
  authRecipient -&gt; E(remote-pubk,
                     remote-ephemeral-pubk
                     || nonce
                     || 0x0)
</pre>

@see <a href=
    "https://github.com/ethereum/devp2p/blob/master/rlpx.md#encrypted-handshake">Structure of the
    responder response</a>
ethereum/p2p/src/main/java/org/hyperledger/besu/ethereum/p2p/rlpx/handshake/ecies/ResponderHandshakeMessageV1.java