PNGme

Command line utility that lets you hide secret messages in PNG files.

Below on the left is original image and on the right modified image with embedded secret message:

Program has 4 commands:

1. Encode a message into a PNG file;
2. Decode a message stored in a PNG file;
3. Remove a message from a PNG file;
4. Print a list of PNG chunks that can be searched for messages.

Idea

I made this program just for fun and Rust learning purposes. Idea come from PNGme resource by picklenerd.
Great about this project is:

Unlike many of the other tutorials you may have worked through, I will not be providing any completed code. The first three chapters come with comprehensive unit tests that will ensure your code has the features it needs. You'll use your unit tested code to complete the remaining chapters.

This is supposed to be your project, not mine. You can use as much or as little of this material as you want.

I definitely can recommend completing it if you want some more advanced project than 'hello world'. Also, it's not so time-consuming and fun to program.

Usage

Command line arguments are parsed using clap:

Utility that lets you hide secret messages in PNG files

USAGE:
    pngme <SUBCOMMAND>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    decode    Searches for a message hidden in a PNG file and prints the message if one is found
    encode    Encodes a message into a PNG file and saves the result
    help      Prints this message or the help of the given subcommand(s)
    print     Prints all of the chunks in a PNG file
    remove    Removes a chunk from a PNG file and saves the result

Firstly you can print all chunks from image:

$ ./target/release/pngme print images/dice.png
[1] Chunk "IHDR" len:13
[2] Chunk "sRGB" len:1
[3] Chunk "gAMA" len:4
[4] Chunk "pHYs" len:9
[5] Chunk "IDAT" len:65445
[6] Chunk "IDAT" len:45941
[7] Chunk "IEND" len:0

Then you can encode secret data:

$ ./target/release/pngme encode images/dice.png RuSt 'secret message'

# make sure data is written
$ ./target/release/pngme print images/dice.png
[1] Chunk "IHDR" len:13
[2] Chunk "sRGB" len:1
[3] Chunk "gAMA" len:4
[4] Chunk "pHYs" len:9
[5] Chunk "IDAT" len:65445
[6] Chunk "IDAT" len:45941
[7] Chunk "IEND" len:0
[8] Chunk "RuSt" len:14

View encoded secret data:

$ ./target/release/pngme decode images/dice.png RuSt
Chunk "RuSt" len:14
Data: secret message

Remove message:

$ ./target/release/pngme remove images/dice.png RuSt
Chunk "RuSt" len:14
Data: secret message

# check chunk was removed
$ ./target/release/pngme print images/dice.png
[1] Chunk "IHDR" len:13
[2] Chunk "sRGB" len:1
[3] Chunk "gAMA" len:4
[4] Chunk "pHYs" len:9
[5] Chunk "IDAT" len:65445
[6] Chunk "IDAT" len:45941
[7] Chunk "IEND" len:0

Also, data can be encoded and decoded as raw bytes:

$ cat images/icon.png | ./target/release/pngme encode images/dice.png RuSt -o out.png

$ ./target/release/pngme print out.png
[1] Chunk "IHDR" len:13
[2] Chunk "sRGB" len:1
[3] Chunk "gAMA" len:4
[4] Chunk "pHYs" len:9
[5] Chunk "IDAT" len:65445
[6] Chunk "IDAT" len:45941
[7] Chunk "IEND" len:0
[8] Chunk "RuSt" len:8434

$ ./target/release/pngme decode out.png RuSt --raw | sha256sum
faf6c846f171423c820a400164300d96197656d2d553c5a98ca41d7e36c339af  -

$ sha256sum images/icon.png
faf6c846f171423c820a400164300d96197656d2d553c5a98ca41d7e36c339af  images/icon.png