PNG chunk analyzer
Walk a PNG chunk by chunk, validate CRCs, read tEXt and zTXt metadata, and find data hidden after IEND or in non-standard chunks.
Open in ctfpalA PNG is a sequence of length-prefixed chunks, each with a four-letter type and a CRC32. That rigid structure makes tampering detectable and makes hiding places obvious once you know where to look.
Walking the chunk list is therefore a complete audit of the file rather than a search: every byte of a PNG belongs to some chunk, so anything that does not fit the chunk structure is, by definition, not supposed to be there. That is a much stronger position than hunting through a format with optional or variable-length regions.
The four places data hides
- After IEND.
IENDis the terminator; every viewer stops there. Bytes after it are free space, and they are usually another whole file. - In tEXt, zTXt, and iTXt chunks. Legitimate metadata chunks that hold arbitrary text, compressed in the zTXt case.
- In unknown chunk types. Decoders ignore chunks they do not recognise if the type’s first letter is lowercase (the 'ancillary' bit). An author can invent
stEgand every viewer will skip it silently. - In the pixel data itself. That is LSB steganography, a different technique with a different tool.
Part of a module
7. File forensics and carving
Identify files by their bytes, find data appended past a format’s end marker, and pull evidence out of images and documents.
Practise on real challenges
Go deeper
- A workflow for image steganography, from magic bytes to bit planesStego challenges reward order, not inspiration. The sequence that finds the payload: container checks before pixel checks, structure before statistics, and the specific tells that separate a PNG trick from a JPEG one.
Related tools
JPEG marker and segment analyzer
Parse JPEG markers, read APP segments and comments, and extract data appended after the end-of-image marker.
LSB steganography extractor
Extract least-significant-bit data from images across every channel, bit order, and traversal direction, with bit-plane visualisation.
Automatic steganography solver
Throw every applicable steganography technique at a file at once - image, audio, archive, text, and document - recursively unpack what falls out, and surface flag matches.
File type identifier by magic bytes
Drop a file and identify what it really is from its signature, regardless of extension. Also finds file headers embedded inside other files.