Hidden words in the "blind watermark"? This is not the best way to hide information...

In 2007, the rock band Nine Inch Nails released the album Year Zero. Before officially releasing the album, they left Easter eggs at the venue. An audience member found a USB drive in the bathroom of the venue, which contained the upcoming new song My Violent Heart.

The song in the USB flash drive is not the same as the officially released version. People found that there was a few seconds of noise at the end of the song in the USB flash drive.

In order to see what the extra noise was, someone put the audio file into professional music software. At this time, a hand appeared in the spectrum graph.

The hand hidden in the music's spectrum (left) is identical to the hand that appears out of thin air on the album cover (right).

Few people would have thought that there are hidden pictures in the art of listening. People have long used this counterintuitive method to secretly convey some "inaudible" information.

Information that cannot be heard

Hiding images in music files has always been one of the basic operations for electronic musicians.

British electronic musician Aphex Twin always likes to spoof his own face. In 1999, he printed his face directly at the end of the song "Equation". When people put this strange music into the music editor, they were shocked.

In the last few seconds of the music, you will "hear" a face | Maxdamantus/Yotube

After signal transformation, people can convert audio to frequency domain for processing. In the spectrum, different colors and positions represent the distribution of different frequency signals. If you don't care whether the final music is good, you can use the spectrum as a canvas and paint the signals in it at will. Some netizens used the picture spectrum conversion software to convert their cat photos into music.

Ideal: Listen to my cat! Reality: Noise. 丨monotoniac/Youtube

People who use the spectrum chart as a canvas are indeed a bit "extreme", because such music sounds very strange and has almost no melody. Using such abnormal music to convey hidden information is easy to be exposed. Other operations can make the message more covert.

In 2010, the Colombian military planned to deliver information to soldiers captured by anti-government forces. The information delivered was likely to be seen by the anti-government forces, which posed a certain risk. Therefore, they needed to hide the information. According to people who had been rescued before, they could listen to the radio when they were captured. So the military contacted the music producer and made a pop song Better Day and played it on a small radio station covering the jungle area. In this song, there is Morse code hidden. It is reported that the hostages who were later released mentioned the hidden message in the song:

"19 rescued. You are next. Don't lose hope."

Paul Dancstep/Vimeo

Hiding information in audio may be a little far from people's lives. However, in the field of images, "steganography" has long been a trick to conceal the truth.

Picture: I'm pretty good at pretending

Hiding information has always been one of the "hard needs" of human beings. The purpose of steganography is to allow only specific people to know the information being transmitted. Some people deceive your hearing, and some people try to deceive your vision.

At the beginning of this year, Douban was "scolded on the hot search" because of a screenshot of an app. Some netizens found that in order to prevent unauthorized transfer, Douban embedded a "blind watermark" in the page that is difficult to detect with the naked eye. The content includes the screenshot user ID, the screenshot post ID, and the screenshot time. The color of these watermark texts is similar to the background color, and people can hardly distinguish them with the naked eye.

These watermark information can be seen in dark mode丨PConline

Is it a picture or a compressed file?

In the era when online disks had not yet become mainstream and "seed resources" dominated the world, "seeds" seemed to have become synonymous with pirated resources on the Internet. Of course, seeds of pirated resources would be banned. In order to continue sharing these resources, people came up with a very secret method: hiding seed files in pictures and making them "picture seeds". When you download a jpg picture to your computer and change the extension to .rar, you can get a compressed package containing the seed file.

Image generator on the Internet

This hiding technique is not difficult. For image files, the file data contains the start identifier and the end identifier. When you open the image with an image browser, the browser will only recognize the data as the image part, and then display the image from the start identifier to the end identifier. Therefore, people can continue to add data after the end identifier and it will not be discovered by the image browser.

However, this kind of image steganography that adds data can only hide from the naked eye of auditors. Once it encounters scanning software, the entire file information will be scanned out.

Is adding data dangerous? Then just "change the picture"

The image itself is actually a series of pixel color data. If you make a small change to this data, you can embed information into the image. For example, by modifying the least significant bit (LSB) of each pixel, you can hide information in the image without causing any disturbance.

Top left. My editor colleague Mai Mai’s cute cat.

Top right. The Guokr logo is hidden in the cat. Doesn’t it look the same as on the left?

Next. Extract the lowest bit information of the upper right image to get the hidden Guokr logo.

In addition, the attribute information and frequency domain information of the image can become carriers for hiding other information. Through these methods, all kinds of images can be hidden with additional information. Therefore, some hackers have also taken advantage of this "ride". Virus files, phishing websites... hiding malicious codes under seemingly normal carriers has also become one of the reasons why computers are often infected.

Image containing virus code

It is not difficult to try out simple steganography. There are many online websites and tools that allow you to hide information directly in images. On these websites, you only need to upload a photo and fill in the information you want to hide, and the program will write the information into the image. Others only need to upload the hidden image to the website and click "decrypt" to extract the information.

Since the development of steganography, the carriers have been constantly updated. From ordinary written text to data codes, and even using DNA as a carrier, people are still exploring new ways to hide information. Perhaps for ordinary people, steganography is just a pastime that they try occasionally. But for information security personnel, how to better hide and discover information will always be one of the important research topics.

When you take a screenshot, some apps will secretly mark your information on the picture; a seemingly normal picture will become a seed if the suffix is ​​changed to rar; a picture will become another picture after being decoded by software - all of the above fall into the category of image steganography.

References

[1] Douban was exposed for adding blind watermarks to screenshots, including user UID and other information. https://www.ithome.com/0/603/924.htm

[2] Steganography. Wikipedia. https://en.wikipedia.org/wiki/Steganography

[3] Yildirim, Melih. "Steganography-based voice hiding in medical images of COVID-19 patients." Nonlinear Dynamics 105.3 (2021): 2677-2692.

[4] Michael Raggo, Chet Hosmer. Data Hiding Technology Revealed: Cracking Secret Data in Multimedia, Operating Systems, Mobile Devices and Network Protocols[M]. Machinery Industry Press, 2014.

[5] Image Steganography. https://incoherency.co.uk/image-steganography/

[6] Channalli, Shashikala, and Ajay Jadhav. "Steganography an art of hiding data." arXiv preprint arXiv:0912.2319 (2009).

[7] Is the Image Hidden in Aphex Twin's "Equation" the Best Easter Egg in Electronic Music? https://www.vice.com/en/article/nzm7mz/aphex-twin-easter-egg

[8] Aphex Twin. Wikipedia. https://en.wikipedia.org/wiki/Aphex_Twin#cite_note-WinlickChart-74

[9] Johannes Trithemius, Archmage of Secrets. https://medium.com/@dzanemorris/johannes-trithemius-archmage-of-secrets-9fc0e7bde40d

[10] Reeds, Jim. "Solved: The ciphers in book III of Trithemius's Steganographia." Cryptologia 22.4 (1998): 291-317.

[11] Li Xuan, Chen Yan. Application and analysis and testing methods of steganography in cyberspace security[C]//. Proceedings of the 2019 Internet Security and Governance Forum., 2019: 199-203. DOI: 10.26914/c.cnkihy.2019.023084.

[12] Gao Hualing. A review of key information hiding technologies[J]. Electronic World, 2016(09):146+148. DOI:10.19353/j.cnki.dzsj.2016.09.109.

[13] Steganographic Decoder. https://www.xhcode.com/converter/steganographic-decoder.html

[14] Cui, Meiying, and Yixin Zhang. "Advancing DNA Steganography with Incorporation of Randomness." ChemBioChem 21.17 (2020): 2503-2511.

Author: Owl

Edit: Window knocking rain

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