Using SCP Port Knocking Remote Hosts

The scripts I posted to open SSH connections through port knocking are very useful to me. But when it comes to transferring files with SCP, port knocking is a nightmare. So I’ve done a similar bash function that automatically deals with the knocks before starting the scp command.

I’ve introduced a delay of 0.5 seconds between the knocks, because I noticed that sometimes the server was not responding to the knocks. The gist code available at GitHub for the pssh() bash function has also been updated with the delay.

#!/bin/bash

# SCP Connection Port Knocker
#
# 1 - Append this code to your .bashrc or .bash_profile file
# 2 - Create a .portknocks file in your home directory with a list like
# host1 port1
# host1 port2
# ...
# host1 portN
# host2 port1
# ...
# 3 - You must open a new terminal session to use the new function
# 4 - Use it as you would use the ssh command
# scp user@server:~/hello ~/hello => psscp user@server:~/hello ~/hello
#
# It accepts the usual options of the SCP program

psscp() {
  while getopts "dfl:prtvBCc:i:P:q1246S:o:F:" FLAG
  do
true
done

j=$OPTIND
  while [ ${@:$j:1} ]
  do
HOST=${@:$j:1}
    HOST=${HOST#*@}
    HOST=${HOST%:*}
    if [ "$HOST" != "." ] && [ "$HOST" != ".." ]
    then
HOSTS="${HOSTS}${HOST}\n"
    fi
    ((j++))
  done

echo -e $HOSTS | sort -u | \
  while read HOST
  do
if [ $HOST ]
    then
CNT=1
      cat ~/.portknocks | grep ^$HOST | awk '{ for(i=2; i <= NF; i++) printf "%s\n", $i}' | \
      while read PORT
      do
echo "Knocking $HOST ($CNT)"
        nc -w 1 $HOST $PORT & sleep 0.5 &&
        ((CNT++))
      done
fi
done

scp $*
}

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            psscp.sh
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