image-file-hider

A simple tool to embed encrypted files into an image while preserving the original image data

Description

This tool contains 4 main files:

• enc.py is the original encoder. It takes an input file and encodes that into an image key.jpg
• dec.py is the original decoder. It takes an input image and decodes it into a file as specified by the user
• encfast.py is the chunk-optimized encoder. It takes an input image and input file, encoding the latter into the former. It uses threaded chunk encoders with a modifiable CHUNKSIZE variable
• decfast.py is the chunk-optimized decoder. It takes an input image and decodes it. It uses threaded chunk decoders with a modifiable CHUNKSIZE variable

How encoding works

Input: File, Key

• Read the file as bytes into Data
• Create a copy of the key and reverse it. We will call this Rkey
• Create an empty set of bytes containing our output data. We will call this Out
• Iterate over [0...len(Data)-1] such that Out[i] = Data[i] xor Key[i%len(key)] xor Rkey[i%len(key)]
• Save Out to a temporary file
• Write 256 blank bytes to the end of the file
• In these 256 bytes, write the numeric length of the file you have just encoded
• Combine the bytes of the image and of the temporary file to get an encoded image file
• Delete the temporary file

How decoding works

Input: File, Key

• Read the file as bytes into DataRaw
• From the last 256 bytes of dataraw, extract the file length as Flen
• Read flen number of bytes from the end file (excluding the block of 256 bytes) and save it as Data
• Create a copy of the key and reverse it. We will call this Rkey
• Create an empty set of bytes containing out output data. We will call this Out
• Iterate over [0...Flen-1] such that Out[i] = Data[i] xor Key[i%len(key)] xor Rkey[i%len(key)] (The inverse operation of XOR is XOR itself!)
• Save Out to an output file to get the extracted data

How chunking works

This concept is inspired by Compute Shaders, and how they read and write to the same texture simultaneously

• Create a constant CHUNKSIZE. In this code, it is 16777216 bytes (16 mb)
• Create a buffer Databuffer with n empty bytes where n is the number of bytes to encode/decode. This is our data
• Set the number of chunks chunkCount to ceil(n/CHUNKSIZE)
• Create a buffer Statbuffer with chunkCount number boolean values, all False to begine with. This is our status
• Create a chunk encoder/decoder as follows:
  • Input: int id
  • Set the variable Start to id*CHUNKSIZE
  • Set the variable End to the minimum of len(Databuffer) and Start+CHUNKSIZE
  • Iterate over [Start...End-1] taking current index i and writing to Databuffer[i]
  • Upon loop completion, set Statbuffer[id] to True to confirm that this chunk has been completed
• For every value [0...chunkCount-1] create a chunk encoder/decoder with id = i
• Create an empty while loop that runs while all values in Statbuffer are not True
• Upon loop completion, treat Databuffer like Out in the previous examples