Encrypt Information In Images Without Distortion

Nomikos writes "C|Net reports: Researchers have created a new way to encrypt information in a digital image and extract it later without any distortion or loss of information. A team of scientists from Xerox and the University of Rochester said that the technique, called reversible data hiding, could be used in situations that require proof that an image has not been altered."

Comments

Encryption?

[heliocentric]

Isn't it more like steganography? I mean, ok, so we can encrypt the message you store using steg. but are we confusing the two?

Re:Encryption?

[saforrest]

Basically it is a form of steganography. The only thing unique is that the information isn't an arbitrary message, but just enough to label the image.

This is called digital watermarking.

Re:Encryption?

[nuntius]

From reading the paper (college access to IEEE publications sure is nice), the researchers outline two forms of reversible data embedding.

Type I simply embeds the data into the spectrum of the image and uses modulo addition as necessary to prevent overflow. Unfortunately, this causes "salt-and-pepper artifacts" because this sometimes affects the most significant bits in a pixel's representation.

Type II uses the traditional method of overwriting the least significant bits or high-frequency coefficients in the image (depending on image encoding).

What this paper does is describe a method that employs Type II encoding and saves the overwritten bits by compressing them and inserting into the embedded data stream. Unlike simple Type II encodings such as always using the lowest two bits, this paper varies the number of bits which are used in each byte. This value is determined according to their compressibility and other parameters in the image. By doing this, the paper obtains a more efficient tradeoff between storage and distortion.

The journal article is "Reversible data hiding" in IEEE Internation Conference on Image Processing, 2002, volume 2, pages 157-160 http://ieeexplore.ieee.org/servlet/opac?punumber=8 052

Is it really encryption?

[verch]

Sounds like 'encrypt' isnt exactly the right word here. Maybe 'encode' would have been better. From the very tech light article it seems that this is a watermarking technique which somehow embeds the watermark with no distortion of the image whatsoever. Traditional watermarks distort the image, albeit usually not noticeable to the casual naked eye.

Re:Signed Hash

[jonbrewer]

"How is this better than a signed hash of the image?"

A signed hash can be separated from an image, while this type of watermarking cannot.

Re:My bullshit detector is on yellow alert

[ChristopherLord]

Canon does provide support for a "Data Verification Kit" on its latest 1Ds camera. No word on how secure it is, etc.

from here:
"Finally with a nod toward law enforcement the EOS-1Ds is the first digital camera that offers the ability to verify that images are unaltered originals using the Data Verification Kit DVK-E1, consisting of a dedicated IC card and card reader, together with software for Windows 2000/XP. This package is available to verify that EOS-1Ds image files are absolutely unaltered. "

It DOES distort the image!!!

[wirelessbuzzers]

... just reversably, so you can get the original back later. And it isn't watermarking! They use only the LSB, so it won't survive recompression, printing, whatever. You can't encode anything without the image without distorting it, except by permuting the color tables. But that is easily detected and can't store much data anyway.

Re:Holy Cow!! This Is Awesome!

[wirelessbuzzers]

Quoth the parent: They are refering to water marks. This is not about "encryption" or even "stenography". The problem is proving a document is original. Actually, it looks like steg to me. Because to prove a document is unaltered without altering it, you just sign it with your private key. This can't be any better: someone could remove the watermark (it's reversible), alter the message, and "authenticate" that, unless there is a digital signature embedded in the image, in which case why not just attach it to the file? Although it would appear that the original paper is not online, so we can't be sure.

These watermarks vs. Digimarc watermarks

[yerricde]

This is called digital watermarking.

But unlike Digimarc watermarks, this kind of watermark isn't designed to survive being sent through the analog hole.

Some more information I googled

[sambo99]

This stuff is in the process of being patented

The abstract of the paper (Reversible Data Hiding) is: "We present a novel reversible (lossless) data hiding (embedding) technique, which enables the exact recovery of the original host signal upon extraction of the embedded information. A generalization of the well-known LSB (least significant bit) modification is proposed as the data embedding method, which introduces additional operating points on the capacity-distortion curve. Lossless recovery of the original is achieved by compressing portions of the signal that are susceptible to embedding distortion, and transmitting these compressed descriptions as a part of the embedded payload. A prediction-based conditional entropy coder which utilizes static portions of the host as side-information improves the compression efficiency, and thus the lossless data embedding capacity"

In case anyone is interested.