Prompt

The hackers have hidden a message in this image. Find out what it is.

Walk-Through

This challenge will give you experience using basic Linux tools to find messages hidden with steganography. An image was altered slightly to embed a hidden flag somewhere in the raw binary of the image.

Questions

What is the hidden flag in the image?

The hidden flag can be found by using the Linux strings program.

Recall from the Bases challenge about how data can be converted from one form to another. Some values in binary that are used in files are not convertible to text characters. strings will pull any binary data out of the file that corresponds to a text character. Text characters would include letters (abc), numbers (123), or symbols (&^,*).

The output of the strings command can be searched with another command; grep.

grep is a powerful search command that looks for characters matching the exact string entered by the user. grep is often used with the pipe character ( | ) to search the output of other commands or to format the output of grep.

This challenge specifies that a flag is contained in the image, therefore, grep could be used to look for binary data that converts to characters resembling the standard flag format. This can be done using the command below:

strings Steg1.jpg | grep SKY

Using strings is a quick way to see if a flag is hidden within the file without needing to open other programs. However, this challenge could also be solved using a hex editor and searching for “SKY”.

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