SkypePatcher

extract.sh

#!/bin/bash

i=0
while read p; do
  IFS="-" read -ra ADDR <<< "$p"
  n="${ADDR[0]}"
  start="${ADDR[1]}"
  end="${ADDR[2]}"

  echo "$start $end"
  xxd -s "$start" -l "$(expr $end - $start)" -p skype | tr -d "\\n"  | xxd -p -r -g0 > "$n.png"
done <output

insert.sh

#!/bin/bash

def=$1
slot=$2
image=$3

while read p; do
  IFS="-" read -ra ADDR <<< "$p"
  n="${ADDR[0]}"
  start="${ADDR[1]}"
  end="${ADDR[2]}"

  if [[ "$n" -eq "$slot" ]]; then
  	break
  fi
done < "$def"

maxSize="$(expr $end - $start)"
echo "Max size is: $maxSize"

newSize=$(stat -c%s "$image")
echo "New size is: $newSize"

if [[ $newSize -gt $maxSize ]]; then
	echo "ERROR: new size is bigger than the original"
	echo "	New: $newSize, Original: $maxSize"
	exit 1
fi

cat "$image" | dd of=skype bs=1 seek=$start conv=notrunc

pngident.py

#!/bin/env python
from string import find
from sys import argv

headers = [(("PNG",1), ("IEND",4))]
filepath = "skype"
outpath = "output"
if len(argv)>2:
	filepath = argv[1]
	outpath = argv[2]

fh = open(filepath, 'rb')
dat = fh.read()
fh.close()

with open(outpath, "w") as f:
	for start,end in headers:
		(sw, soff) = start
		(ew, eoff) = end
		x = 0
		y = 0
		n = 0
		while 1:
			x = find(dat,sw,x+1)
			if x<0: break
			y = find(dat,ew,x+1)
			if y<0: break
			print sw,"file begins at byte",x - soff,"ends at",y - eoff
			f.write(str(n) + "-" + str(x-soff) + "-" + str(y+len(ew)+eoff) + "\n")
			n += 1