added BitShade

README.md

@@ -14,3 +14,4 @@
 * [Image Transfer](./it.sh): a more convenient wrapper around dd for writing and reading removable media images
 * [Mount Manager](./mm.sh): a simple script to mount/unmount removable media partitions
 * [PNGizer](./pngizer.sh): an utility (and a shell library) to convert any file or directory to/from a PNG image
+* [BitShade](./bitshade.sh): a steganographic tool for hiding any data file inside a PNG image

bitshade.sh

@@ -0,0 +1,79 @@
+#!/bin/sh
+# BitShade: a simple POSIX-compatible tool for
+# image-based steganography
+# Depends on od, paste, dd, awk, sed, ImageMagick and pngcrush
+# Usage:
+# - encoding: bitshade.sh e [cover image] [file to hide] [output PNG]
+# - decoding: bitshade.sh d [container PNG] [output file]
+# Created by Luxferre in 2026, released into public domain
+
+# encode raw file as a netstring
+to_netstring() {
+  printf '%d:' "$(cat "$1" | wc -c)"
+  cat "$1"
+  printf ','
+}
+
+# decode a raw file from a netstring (inside another file)
+from_netstring() {
+  # get the container length
+  flen=$(head -n 1 "$1" | cut -f 1 -d :)
+  # skip the length itself and the : char
+  dd if="$1" of="$2" skip=$((${#flen} + 1)) bs=1 count=$flen
+}
+
+# for every input byte, print its bits
+conv_input() {
+  to_netstring "$1" | od -An -tu1 -v -w1 | awk '{n=int($0);for(i=0;i<8;i++){print(n%2);n=int(n/2)}}'
+}
+
+# assemble a file bit by bit
+collect_bits() {
+  outfile="$1"
+  tfile2=$(mktemp)
+  tfile3=$(mktemp)
+  awk 'BEGIN{n=0;b=1} {n+=b*int($1);b*=2;if(b==256){printf("\\%03o",n);n=0;b=1}}' > $tfile2
+  printf "$(cat $tfile2)" > $tfile3
+  from_netstring $tfile3 "$1"
+  rm -f $tfile2 $tfile3
+}
+
+# stego_encode cover_image hidden_text out.png
+stego_encode() {
+  coverfile="$(mktemp)"
+  infile="$(mktemp)"
+  tfile="$(mktemp)"
+  temp_ppm="$(mktemp)"
+  magick $1 -compress none ppm:$temp_ppm
+  cat $temp_ppm | head -n 3 > $tfile
+  cat $temp_ppm | tail -n +4 | sed 's/\s\+/\n/g' > $coverfile
+  conv_input "$2" > $infile
+  paste $coverfile $infile | awk '{print(NF>1?int(int($1)/4)*4+int($2)*2+(rand()>0.5?1:0):$1)}' >> $tfile
+  magick ppm:$tfile png:$3
+  pngcrush -ow $3
+  rm -f $coverfile $infile $temp_ppm $tfile
+}
+
+# stego_decode in.png out_file
+stego_decode() {
+  temp_ppm="$(mktemp)"
+  magick $1 -compress none ppm:$temp_ppm
+  cat $temp_ppm | tail -n +4 | sed 's/\s\+/\n/g' | awk '{x=int($0)%4;print(x<2?0:1)}' | collect_bits "$2"
+  rm -f $temp_ppm
+}
+
+# entry point
+
+if [ "$1" = "e" ]; then
+  [ -z "$2" ] && echo 'No cover file specified! Exiting...' && exit 1
+  [ -z "$3" ] && echo 'No input file specified! Exiting...' && exit 1
+  [ -z "$4" ] && echo "No output file specified! Exiting..." && exit 1
+  stego_encode "$2" "$3" "$4"
+elif [ "$1" = "d" ]; then
+  [ -z "$2" ] && echo 'No input file specified! Exiting...' && exit 1
+  [ -z "$3" ] && echo "No output file specified! Exiting..." && exit 1
+  stego_decode "$2" "$3"
+else
+  echo 'Invalid mode! Use e for encoding or d for decoding'
+fi
+