#!/bin/bash
read -p 'Enter the number of bits: 40, 64, 104, 128, 152, 232, or 256: ' bits
case $bits in
40|64|104|128|152|232|256) count=$(( $bits / 8 )) ;;
*) echo "Not a valid number of bits: $bits" ; exit 1 ;;
esac
dd if=/dev/random bs=1 count=$count 2>/dev/null \
| od -t x1 \
| sed -e 's/^[^ ]*//' -e 's/ /-/g'