Description
Most-significant-bit steganography hides the flag in RGB channel bit 7. Use Stegsolve’s data extractor to dump the relevant rows.
Setup
Install Stegsolve (or an equivalent tool) and open the provided PNG.
Use Analyse → Data Extract, set bit order to MSB First, and enable Red 7, Green 7, Blue 7. Scroll to the top of the extracted text.
wget http://www.caesum.com/handbook/Stegsolve.jar -O stegsolve.jar
chmod +x stegsolve.jar && java -jar stegsolve.jar
Solution
- Step 1Extract MSB dataThe textual payload appears when you extract only the 7th bits of each color channel. Save the text and scan for picoCTF.
- Step 2Search the dumpUse grep or strings on the saved text file to locate the flag and copy it out (remove any spaces).strings text | grep pico
Flag
picoCTF{15_y0ur_que57...d55bee}
Only the MSB bits carry useful data, so LSB analysis will pass but yield nothing.