A QR Code Based Zero-Watermarking Scheme for Authentication of Medical Images in Teleradiology Cloud

Algorithm 2

Watermark construction.

𝐈𝐧𝐩𝐮𝐭: Host image 𝐇 of size 𝐍×𝐍, Secret Share 𝐒𝐬𝐡𝐚𝐫𝐞 of size 𝐦×𝐦, Key (𝐤_𝐢,𝐤_𝐣) for initial

     block Selection, size of block 𝐛×𝐛, Number of iterations 𝐢 for Arnold Transform

  𝐎𝐮𝐭𝐩𝐮𝐭: Watermark 𝐖 of size 𝐦×𝐦

Step  1. Apply Contourlet Transform on 𝐇 to generate a 𝐧×𝐧 LF subband

Step  2. Perform a 𝐛×𝐛 block partitioning on the LF subband to generate 𝐧/𝐛×𝐧/𝐛 overlapping

   blocks

Step  3. Perform steps 4–9 for each element of 𝐒𝐬𝐡𝐚𝐫𝐞

Step  4. Apply Arnold transform on (𝐤_𝐢,𝐤_𝐣) to select a block for Master Share creation;

   Increment 𝐤_𝐢 and 𝐤_𝐣 by 1; i.e., 𝐤_𝐢=𝐤_𝐢+1 and 𝐤_𝐣=𝐤_𝐣+1

Step  5. Apply SVD to selected block to generate 𝐔,𝐒 and 𝐕 matrices

Step  6. Compute the Hu’s invariant moments 𝐈_𝟏,𝐈_𝟐 and 𝐈_𝟑 for the diagonal matrix 𝐒

Step  7. Create a 3 bit Master Share 𝐌𝐬𝐡𝐚𝐫𝐞 out of the sign bits of 𝐈_𝟏,𝐈_𝟐 and 𝐈_𝟑

Step  8. Compute C from Sshare with equation (10);

   i.e., 𝐂=sqrt(8∗𝐒𝐬𝐡𝐚𝐫𝐞+1)−1/2 where 𝐂=sum(𝐌𝐬𝐡𝐚𝐫𝐞,𝐒𝐖)

Step  9. Subtract 𝐌𝐬𝐡𝐚𝐫𝐞 from 𝐂 to get 𝐒𝐖

Step  10. Apply Arnold Transform to unscramble 𝐒𝐖 to get 𝐖