file_splitter.sh

This is a simple bash script to split a file into pieces based on provided file size and encrypt the chunks individually.

The script also provides option to decrypt them and re-combine them. Useful in cases you want to upload/download files over an insecure connection with limited upload/download size limit.

#!/bin/bash
set -euo pipefail
IFS=$'\n\t'

SPLIT_FILE_EXTENSION=".txt"
CHUNK_SIZE=18000000
PASSWORD=password

function splitter(){
  if [ -z "$1" ] || [ $1 = "-s" ] 
  then
    echo "Missing Argument: No file path for the file to split"
    return 1
  fi

  local FILENAME=$1
  PREFIX=$(tr -dc A-Za-z0-9 < /dev/urandom | head -c 10 ; echo)

  split --bytes=$CHUNK_SIZE --additional-suffix=$SPLIT_FILE_EXTENSION -d $FILENAME $PREFIX
  
  SPLIT_FILES=$(ls | grep "$SPLIT_FILE_EXTENSION")

  mkdir fenc
  for file in $SPLIT_FILES
  do
    openssl enc -aes-256-cbc -base64 -pbkdf2 -iter 100000 -pass pass:$PASSWORD -in $file -out fenc/$file
  done

  rm *$SPLIT_FILE_EXTENSION 
  mv fenc/* ./
  rm -rf fenc
}

function assembler(){
  if [ -z "$1" ] || [ $1 = "-a" ] 
  then
    echo "Missing Argument: No file path for the file to split"
    return 1
  fi

  local FILENAME=$1
  SPLIT_FILES=$(ls | grep "$SPLIT_FILE_EXTENSION")

  mkdir fenc
  for file in $SPLIT_FILES
  do
    openssl enc -d -aes-256-cbc -base64 -pbkdf2 -iter 100000 -pass pass:$PASSWORD -in $file -out fenc/$file
  done
  
  rm *$SPLIT_FILE_EXTENSION 
  mv fenc/* ./
  rm -rf fenc

  cat *$SPLIT_FILE_EXTENSION > $FILENAME
  rm *$SPLIT_FILE_EXTENSION
}

function help_screen(){
  echo "./splitter.sh [FLAGS] [FILENAME]"
  echo "FLAGS:"
  echo "-a <filename>: Assemble split files and save as filename."
  echo "-s <filename>: Split file into encrypted chunks."
  echo "-h: To display the help screen."
}

while getopts sah flag
do
  case "${flag}" in
    s) splitter ${BASH_ARGV};;
    a) assembler ${BASH_ARGV};;
    h) help_screen;;
    ?) echo "incorrect flag passed";;
  esac
done

Instructions

1. Make the script executable with
   sudo chmod +x file_splitter.sh
   If you name your script file something else, replace
   file_splitter.sh with your filename.

2. Create an empty directory and execute the split script:
   ./file_splitter.sh -s <path-to-file-you-want-to-split>
   All the split files will be stored inside this empty directory. To specify password for encryption, edit the PASSWORD=password field to another name (will add a flag in the future).
   Important Note: The split files will be in the .txt format, so make sure there are no other txt files in the directory initially (all txt files will be purged midway using regex in the working directory).

3. To re-assemble the file on the other side, simply use the command
   ./file_splitter.sh -a
   inside the directory where you have placed all the file chunks.
   Same rule applies as to the splitting process, make sure that the directory only contains the split files. Also, make sure the password is same on both sides.