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Aperi'Solve v.3.2.4

Bit-plane decomposer

The decomposer is Aperi'Solve's own analyzer (pure Python, using Pillow and NumPy). It splits the uploaded image into its bit planes: for every color channel (red, green, blue, alpha — or grayscale) and every bit position 0–7, it renders a black-and-white image where each pixel shows only that single bit.

Why bit planes reveal steganography

In a natural photograph, high bits (7, 6...) carry the visible structure and low bits look like random noise. LSB steganography overwrites the low bits with payload data — which is not photographic noise. When that happens, the bit-0 plane suddenly shows:

  • clean geometric shapes, text or QR codes,
  • uniform regions where noise should be,
  • a sharp boundary where the payload ends and true noise resumes.

Reading the results

Aperi'Solve shows, for each bit position:

  1. Superimposed RGB planes — the RGB channels of one bit combined into a color image. Fastest way to scan all bits.
  2. Per-channel planes — Red, Green, Blue (and Alpha) separately. Payloads often live in a single channel, invisible in the superimposed view.

Look at bit 0 and bit 1 first: legitimate image content rarely produces structure there.

Pay special attention to the alpha plane — a fully opaque image has a constant alpha channel, so any texture in the alpha planes is attacker-added data.

Extracting what you see

Seeing a QR code or text in a plane is often enough (scan/read it). To extract embedded bytes rather than pixels, use zsteg with the matching combination, e.g. data visible in the red LSB plane:

$ zsteg -E "b1,r,lsb,xy" image.png > payload.bin

Reproducing locally

StegSolve offers the same per-plane browsing as a desktop Java app, and GIMP's channel decomposition (Colors > Components > Decompose) achieves similar results.

Common CTF patterns

  • A QR code in the bit-0 plane of one channel.
  • Text visible only in the alpha channel planes.
  • Two images blended: one visible normally, one appearing in low bit planes.
  • Payload only in the top strip of the bit plane — the message was shorter than the image, encode order xy.