dotnet-alphasecret

.NET Core implementation of Hanno Böck's Alphasecret.

Excerpt from hannob's readme:

GIMP has an unexpected behavior that when "deleting" content from an image with an alpha channel it will not actually delete the content, it will just be marked transparent.

This can have the unintended sideeffect of leaking information if you use GIMP to remove private parts of an image, e.g. a screenshot.

Download

Check out the releases section for the latest builds.

Usage

# Inspect folder:
./AlphaSecret examples

# Inspect single file:
./AlphaSecret examples/color-suspicious.png

# Reading targets from stdin:
ls -1 **/*.png | ./AlphaSecret --stdin

Building from Source

git clone https://github.com/nikeee/dotnet-alphasecret

# Linux:
dotnet publish -c Release --self-contained --runtime linux-x64
# Resulting executable will be in:
./bin/Release/net9.0/linux-x64/publish/AlphaSecret

# Windows:
dotnet publish -c Release --self-contained --runtime win-x64
# Resulting executable will be in:
./bin/Release/net9.0/win-x64/publish/AlphaSecret.exe

# Linux:
dotnet publish -c Release --self-contained --runtime osx-x64
# Resulting executable will be in:
./bin/Release/net9.0/osx-x64/publish/AlphaSecret

Why?

• Calling ImageMagick's convert and piping hexdump into grep works for a few images, but will be slow on millions of images.
• A bash script does not run very well on windows (WSL might help, but it has poor IO performance)

Background

• News article: https://www.golem.de/news/alphakanal-gimp-verraet-geheimnisse-in-bildern-2002-146504.html
• Discusson on Gitlab: https://gitlab.gnome.org/GNOME/gimp/issues/4487