mkeygen

#!/bin/bash

DIR="/dev/shm"
TMPSUBDIR="${DIR}/$(head /dev/urandom | tr -dc A-Za-z0-9 | head -c 32)"
DEFAULTNAME="mkeygen"
SIZE="256"
BLKDEV="/dev/random"

die() {
  echo "$1"
  exit 1
}

help_and_exit() {
  echo "Usage: "
  echo "$DEFAULTNAME"
  echo " <options> /path/to/masterkeyfile"
  echo "Options:"
  echo "    -s, --size         Master key size in bits (must be divisible by 8)."
  echo "    -w, --wipe-temp    Wipe temporary files after creation of master key (It must be used if the master key size is larger than than 512)."
  echo "    -h, --help         It shows this menu."
  exit "$1"
}

while [[ $# -gt 0 ]]; do
  args="$1"
  case ${args} in
    -s|--size)
      SIZE="$2"
      shift

      case ${SIZE} in
          ''|*[!0-9]*) die "-s|--size must be a natural number." ;;
      esac

      if [ "${SIZE}" = "0" ]; then
        die "Size of the key cannot be zero."
      fi
      
      if [ "$(( ${SIZE} % 8 ))" != "0" ]; then
        die "Key size must be multiple of 8."
      fi
    ;;
    
    -w|--wipe-temp)
      if [ "${SIZE}" -lt "512" ]; then
        die "Key size is less than 512. There will be nothing to clean."
      fi
      WIPETMP="y"
      shift
    ;;    

    -h|--help)
      help_and_exit 0
    ;;

    --)
      shift
      break
    ;;

    -*)
      die "$args unknown option."
    ;;

    *)
    break
    ;;
  esac
  shift
done

if [ "$1" = "" ]; then
  help_and_exit 1
fi

  if [ "${SIZE}" -lt "512" ]; then
    dd if=${BLKDEV} count="$(( ${SIZE} / 4 ))" bs=1 &>/dev/null | \
      b2sum --binary --length="${SIZE}" | cut -d " " -f 1 | \
      sed 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf > "$@"
  else
    mkdir -p ${TMPSUBDIR}
      for ((i=1;i<="$(( ${SIZE} / 512 ))";i++)); do
        dd if=${BLKDEV} count=128 bs=1 &>/dev/null > \
        ${TMPSUBDIR}/${DEFAULTNAME}.${i}
      done
      if [ "$(( ${SIZE} % 512 ))" != "0" ]; then
        dd if=${BLKDEV} count="$(( (${SIZE} % 512 ) / 4 ))" bs=1 \
        &>/dev/null > \
        ${TMPSUBDIR}/${DEFAULTNAME}."$(( (${SIZE} / 512 ) + 1 ))"
      fi
      
      cat ${TMPSUBDIR}/${DEFAULTNAME}.1 | b2sum --binary \
        --length=512 | cut -d " " -f 1 | sed \
        's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf > "$@"
        if [ "$(( ${SIZE} / 512 ))" > "2" ]; then
          for ((i=2;i<="$(( ${SIZE} / 512 ))";i++)); do
            cat ${TMPSUBDIR}/${DEFAULTNAME}.${i} \
            ${TMPSUBDIR}/${DEFAULTNAME}."$(( ${i} - 1 ))" | \
            b2sum --binary --length=512 | cut -d " " -f 1 | sed \
              's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf >> "$@"
          done
        fi
        if [ "$(( ${SIZE} % 512 ))" != "0" ]; then
          cat ${TMPSUBDIR}/${DEFAULTNAME}."$(( (${SIZE} / 512 ) + 1 ))" \
            ${TMPSUBDIR}/${DEFAULTNAME}."$(( (${SIZE} / 512 ) ))" | \
            b2sum --binary --length="$(( ${SIZE} % 512 ))" | cut -d " " \
            -f 1 | sed 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs \
            printf >> "$@"
        fi
        if [ "${WIPETMP}" = "y" ]; then
          shred --iterations=10 --zero -u ${TMPSUBDIR}/* &>/dev/null
        fi
    rm -rf ${TMPSUBDIR}
  fi