Add post-quantum support

main.go

@@ -18,6 +18,9 @@ func main() {
 		log.Fatal("COMMAND environment variable must be set")
 	}
 	config := &ssh.ServerConfig{
+		Config: ssh.Config{
+			KeyExchanges: []string{"mlkem768x25519-sha256", "curve25519-sha256", "ecdh-sha2-nistp256", "ecdh-sha2-nistp384", "ecdh-sha2-nistp521", "diffie-hellman-group14-sha256", "diffie-hellman-group16-sha512"},
+		},
 		NoClientAuth: true,
 	}
 	_, key, err := ed25519.GenerateKey(rand.Reader)
@@ -51,6 +54,9 @@ func handleConn(conn net.Conn, config *ssh.ServerConfig) {
 		conn.Close()
 		return
 	}
+	if acm, ok := sshConn.Conn.(ssh.AlgorithmsConnMetadata); ok {
+		log.Println("Negotiated KEX:", acm.Algorithms().KeyExchange)
+	}
 	log.Println("New connection from", sshConn.RemoteAddr(), "user", sshConn.User())
 	go ssh.DiscardRequests(reqs)
 	for newChannel := range chans {
@@ -142,4 +148,4 @@ func runCommand(channel ssh.Channel, command string) {
 	go io.Copy(channel, stdout)
 	go io.Copy(channel, stderr)
 	cmd.Wait()
-}
+}