Efficient Two-Step Protocol and Its Discriminative Feature Selections in Secure Similar Document Detection

Algorithm 2

Protocol of the generic two-step solution SSDD-FS.

Protocol   SSDD-FS

   and are -dimensional document vectors; and are their -dimensional feature vectors.

   Assume that Alice and Bob share the matrices A and of sizes and , respectively.

[1st step] Filtering step in the -dimensional space

Alice:

   Execute Lines to of SSDD-Base for and instead of and A;

Bob:

   Execute Lines to of SSDD-Base for and instead of and A;

   Compute and send it to Alice;

Alice:

   Execute Lines and of SSDD-Base;  //

   Compute and ; //

   Compute ;  //

   if then Discard the pair as a non-similar one; // = upper bound

[2nd step] Post-processing step in the -dimensional space

Alice and Bob:

   Execute Lines to of SSDD-Base if is not discarded in the 1st step;