steghide It is a tool that can be installed in our GNU / Linux distribution and that can be used to practice steganography. And what is that? Well, for those who do not know, steganography is the art of hiding information in texts, images and other types of digital documents (images, videos, sound, ...). Since ancient times it has been used to send secret messages and hide all kinds of information, and today governments continue to use it very often.
En steganography there is a carrier, which in this case will be a jpg image, and a covert information that will be used by carrier as transmission medium. What is intended is that the sender can deliver this information to the receiver without third parties being able to access it easily, that is, it has a similar purpose to cryptography.
To do this, the first thing is install on our steghide system (There are many tools of this type, another option is python-stepic) that will allow us to embed the hidden information in the image. To do this, type:
sudo aptitude install steghide
Now that you have it installed, you just need to take a photograph that you have on hand in jpg format, for example, and a plain text document (.txt) with the message you want to hide. Imagine that the photo is called foto01.jpg and you have saved the message in the file message.txt. Once you have those ingredients, you can generate an image with the hidden text typing in the terminal:
steghide embed -cf foto01.jpg -ef mensaje.txt
It will ask you for a password to protect it. The recipient of the image may retrieve hidden message with the password if you type:
steghide -extract -sf foto01.jpg
If for any reason the photograph is intercepted by a third party, they will not be able to see the hidden message unless they know that it has been embedded and they manage to discover the password, since at first glance it is impossible to tell the difference. Another way to pass "private" messages using an alternative to cryptography...