Special Embedding by using Qtech Hide & View
1. What is "Special Embedding"?
When you embed secret data in a png or bmp image and also output as a png or bmp image, by using Qtech Hide & View (by BPCS-Steganography in general), you can do it in a "special" manner like the following.
Let i be an input image (vessel image), o be the output image (stego image), and s be the secret data. The embedding operation is described by a symbol e.
|(1)||You first transform i to i' according to some reversible transformation operation t. Note that if you take t twice, the image must be the same as before, i.e., i = i/t/t. This transformation process is described by i' = i/t.|
|(2)||Then, you embed s in i' to get a stego image i'(s). So, i'(s) = i/t/e.|
|(3)||Finally, you make another t operation on i'(s) to get o = i'(s)/t = i/t/e/t.|
For example, you can take a "180 degree rotation (r) " for t. So, you first rotate the vessel image by 180 degree (i/r), then embed the secret data (i/r/e), and rotate it again to get the final stego image (o). Therefore, o = i'(s)/r = i/r/e/r. See the following illustration.
This o is "visually" same as the ordinary stego image o0=i(s) = i/e, but it is actually different. o has no clue to show that it was pre-processed by r operation. In this case you cannot extract the embedded data (s) by the direct use of Qtech Hide & View even if you have the correct key (Access Key). You can extract it only when you make an r operation before you start extracting. That is, you must do o/r = i/r/e/r/r = i/r/e before extracting.
It is obviously more difficult for a third party (an attacker) who don't know this special embedding process to steal the embedded data from o than from o0. Steganalysis may be a littler harder, too.
Note that this type of special embedding by way of reversible operations on the vessel image is not only possible for BPCS-Steganography, but is also possible for some other image steganography such as a LSB-steganography (i.e., Least Significant Bit steganography).
2. Reversible operations for Qtech Hide & View
The following table shows typical reversible transformation operations for a BPCS-Steganography program, specifically Qtech Hide & View in either png or bmp output mode.
Symbol of the
Operation (Double-operation brings back
the image to the original image)
|r||Rotation by 180 degree|
Coloring complementation (changing into negative colors)
(Note that h/v = v/h =r)
These transformations are executable by many image-retouching programs. For example, these operations can be done by Microsoft Photo Editor in the following manner.
|h, v||: Image --> Mirror (select horizontal or vertical)|
|r||: Image --> Rotate (select 180 degree)|
|c||: Effect --> Nega (channel R G B) -->OK|
3. Examples of special embedding by Qtech Hide & View
The following images in the table look all the same, but actually they are all different. You can check them after downloading.
|Name of the image file||Explanation of the file||Size of the file|
|1.cameramen.png||Vessel image (i)||1,336KB|
|2.cameramen.53emb.png||Normal embedding (i/e)||1,320KB|
|3.cameramen-h.53emb.h.png||This file was processed as i/h/e/h.||1,453KB|
|4.cameramen-v.53emb.v.png||This file was processed as i/v/e/v.||1,454KB|
|5.cameramen-r.53emb.r.png||This file was processed as i/r/e/r.||1,454KB|
|6.cameramen-c.53emb.c.png||This file was processed as i/c/e/c.||1,452KB|
|7.cameramen-hvc.53emb.cvh.png||This file was processed as i/h/v/c/e/c/v/h.||1,453KB|
(Files 2. - 7. are embedded with a same mp3 sound file. The complexity threshold was set to 53. No Access Key was used.)
The last half of the file names for 3 - 7 show their embedding processes by the characters h, v, r, and c. In order to extract the embedded data, you must step back the way the secret data (mp3 sound file) was embedded.
"5.cameramen-r.53emb.r.png" needs r operation before you start extracting. Set Complexity Threshold =53,
"7.cameramen-hvc.53emb.cvh.png" needs h/v/c (or, r/c) operation before you start extracting. Set Complexity Threshold = 53,
otherwise you can't extract anything.
4. Reversible image transformation using some parameter
The following illustration shows another type of reversible image transformation according to a "split-and-arranging" operation t(k), where "k" is a parameter to produce a specific arrangement pattern. In this example 12 blocks in the original picture (1, 2, 3, 4, ..., 11, 12) are replaced by the blocks in the (11, 5, 1, 10, ..., 4, 2) positions. The reverse operation t-1(k) is the re-arranging operation to recover the original image. The actual t(k) and t-1(k) should be two computer programs. As you can see from this example, a different parameter k need to produce a different image transformation. So, k is an image transformation parameter, or a key to produce a specific transformation.
Original image ( i ) Transformed image ( i')
You can first transform an original image (i) by a secret key (k) to get a transformed image (i'= i/t(k)), and then embed some secret data (s) in i' to get a stego image (i'(s)), and further make a reverse transformation to get a final output image (o=i/t(k)/e/t-1(k)). While, an ordinary embedding is done by o0=i/e operation. There will be no visual difference between i/t(k)/e/t-1(k) and i/e. No one can tell the difference even from the original image (i).
The secret data (s) can be easily extracted from the ordinary stego image (i/e) by using the extracting program, but can never be extracted from the special stego image (o=i/t(k)/e/t-1(k)) without knowing the key (k) to run the program (.t-1(k)).
Therefore, we can conclude from this example that if such t(k) and t-1(k) are implemented as computer programs independent of any specific steganographic program, some types of steganography (including BPCS-Steganography) become much safer. Even a no embedding-key available program (like Qtech Hide & View v02) can work as a key-available program (only for the png and bmp output case).
(1) In case of BPCS-Steganography, the embedding capacity after image transformation (i.e., i'= i/t(k) ) mostly remains unchanged.
(2) Almost all JPEG steganography programs cannot be used in this way because of the nature of the JPEG image data structure. The JPEG output mode in Qtech Hide & View cannot be exceptional.
(3) If someone has implemented a reversible image transformation program (i.e., t(k) and t-1(k) ) and put it on a downloadable place, please let us know about it from the message sending page. We will make a link there.
5. So, what?
BPCS-Steganography (and some other type of steganography, too) can take special embedding information into a part of the embedding/extracting key. And if some reversible image transformation is implemented, it will help some types of steganography programs much securer than the original ones.
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(Updated on Jan. 20, 2015 by Eiji Kawaguchi)