Introduce extra delay before closing unauthenticated sessions To make it harder for attackers, introduce a delay to keep an unauthenticated session open a bit longer, thus blocking a connection slot until after the delay. Without this, while there is a limit on the amount of attempts an attacker can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to handle one attempt is still short and thus for each of the allowed parallel attempts many attempts can be chained one after the other. The attempt rate is then: "MAX_UNAUTH_PER_IP / <process time of one attempt>". With the delay, this rate becomes: "MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".

#! /bin/sh
set -e

test "$1" = 'purge' || exit 0
if test -e /etc/dropbear; then
  rm -f /etc/dropbear/dropbear_rsa_host_key
  rm -f /etc/dropbear/dropbear_dss_host_key
  rmdir --ignore-fail-on-non-empty /etc/dropbear
fi
update-rc.d dropbear remove >/dev/null
rm -f /etc/default/dropbear
rm -rf /etc/dropbear/supervise /etc/dropbear/log/supervise