Mine

#!/bin/bash
while [ 1 ]; do
  DecKey=0
  while [ $DecKey -eq 0 ] || [ $DecKey -eq 255 ] || [ $DecKey -eq 135 ] || \
        [ $DecKey -eq 238 ] || [ $DecKey -eq 122 ] || [ $DecKey -eq 156 ] ; do
    key=$(dd bs=1 count=1 2> /dev/null)
    DecKey=$(( $((`printf "%u" "'$key"`)) & 255))
  done
    echo $DecKey
done
exit 0