Added BlueShift

README.md

@@ -15,3 +15,4 @@
 * [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
+* [BlueShift](./blueshift.sh): a high-density steganographic tool for hiding any data file inside a PNG image

blueshift.sh

@@ -0,0 +1,76 @@
+#!/bin/sh
+# BlueShift: an experimental POSIX-compatible tool for
+# high-density (1 byte per pixel) image-based steganography
+# Depends on od, paste, dd, pr, awk, sed, ImageMagick and pngcrush
+# Usage:
+# - encoding: blueshift.sh e [cover image] [file to hide] [output PNG]
+# - decoding: blueshift.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
+}
+
+# convert PPM to plain RGB list (pixel per line)
+ppm2rgb() {
+  tail -n +4 | sed 's/\s\+/\n/g' | pr -3ta
+}
+
+# for every input byte, print its 2-bit or 4-bit parts
+# R: lsb 2 bits, G: msb 2 bits, B: hsb 4 bits
+conv_input() {
+  to_netstring "$1" | od -An -tu1 -v -w1 | awk '{n=int($0);printf("%u\t%u\t%u\n",n%4,int(n/4)%4,int(n/16))}'
+}
+
+# stego_encode cover_image hidden_text out.png
+stego_encode() {
+  coverfile="$(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 | ppm2rgb > $coverfile
+  conv_input "$2" > $infile
+  paste $coverfile $infile | awk '{if(NF>3)printf("%u %u %u\n", int(int($1)/4)*4+int($4), int(int($2)/4)*4+int($5), int(int($3)/16)*16+int($6));else print($0)}' >> $tfile
+  magick ppm:$tfile png:$3
+  pngcrush -ow $3
+  rm -f $coverfile $infile $temp_ppm $tfile
+}
+
+# stego_decode in.png out_file
+stego_decode() {
+  temp_ppm="$(mktemp)"
+  tfile="$(mktemp)"
+  magick $1 -compress none ppm:- | ppm2rgb | awk '{printf("\\%03o", (int($3)%16)*16 + (int($2)%4)*4 + (int($1)%4))}' > $temp_ppm
+  printf "$(cat $temp_ppm)" > $tfile
+  from_netstring $tfile "$2"
+  rm -f $temp_ppm $tfile
+}
+
+# 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
+