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