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Sharing Numerous Images Secretly with Reduced Possessing Load

Chen C-C., Chien Y-W.

Fundamenta Informaticae

2008

Vol. 86, nr 4

447-458

This work presents a secret image sharing approach for sharing several secret images while reducing each participant's possessing load to only one shared image. The proposed approach employs a random image and a hash function to create corresponding random-like shift images for each secret image, and then publishes the generated images. The random image is then secretly shared to each participant, such that each participant can only possess one shared image to recover the random image, thus enabling the computation of all secret images. The contiguous hash results modify the secret images to random-like public images that are secure for malicious attacks. Experimental results indicate that the proposed method can share several secret images but reduce the possessing load of each participant efficiently. Attacks on shared or public images are also discussed.

Secret Image Hiding and Sharing Based on the (t,n)-Threshold

Chang C-C., Lin C-Y., Tseng C-S.

Fundamenta Informaticae

2007

Vol. 76, nr 4

399-411

This study proposes a new secret image sharing method based on the ( t, n)-threshold. The sharing method is completed through three main steps: (1) quantizing the secret image, (2) generating n shadows from the quantized image, and (3) sharing the n shadows among n cover images. Our goal is both to attain good stego-image and secret image quality preservation effects and to limit the size of each shadow image down to 1/ t of that of the secret image for convenient transmission and storage. In the first step, the secret image is divided into non-overlapping 4 × 4 blocks that are quantized according to the results of block testing. Each block, after the block testing procedure, is judged to be either a smooth block or a non-smooth one. Smooth blocks can be neatly restored after being hidden into the cover image, while non-smooth blocks can be somewhat lossy, but such modification is perceptually invisible. The second step is to apply Shamir's ( t,n)-threshold, which uses a ( t-1)-degree polynomial to generate n shadows so that the secret image can be restored from any t out of n shadows. The last step involves a modulo operation to hide the n shadows in n cover images. According to our experimental results, the PSNR values of the reconstructed secret images by our method center around 39 dB, outperforming other recent methods.