Query-Biased Preview over Outsourced and Encrypted Data

Algorithm 3

Constructing SecARI: 𝙸𝚗𝚍𝚎𝚡_𝐾𝑑,𝑒.

Input:

 (1) 𝑑: the document identifier

 (2) 𝑒=𝑒₁,…,𝑒_𝑛: the keyword-frequency set collection

 (3) 𝐾=𝐾_𝑚,𝐾_𝑝: consists of the master key 𝐾_𝑚 for row encryption

    and the permutation key 𝐾_𝑝 for 𝜋

Output: A secure additive ranking index 𝐻

Method:

 (1) scan 𝑒, extract 𝑚 distinct keywords 𝑤₁,…,𝑤_𝑚

 (2) create an 𝑚×𝑛 data matrix 𝑋=(𝑥_𝑖𝑗), the value of each data 𝑥_𝑖𝑗 is

    the frequency of the keyword 𝑤_𝑖 in the 𝑗th snippet

 (3) for each row 𝑖, the encryption/decryption key is 𝑘_𝑖←𝑓_𝐾𝑚𝑤_𝑖∣∣𝑑.

    Thus the keys for all rows form a vector 𝐊_𝑋=𝑘₁,…,𝑘_𝑚

 (4) create an 𝑚×𝑛 matrix 𝐶, each cell 𝑐_𝑖𝑗 has length 𝑁

 (5) compute 𝐶←𝙲𝚘𝚍𝚎_𝐊𝑋(𝑋) using Matrix-AC

 (6) for all 𝑤_𝑖, set 𝐻𝜋_𝐾𝑝𝑤_𝑖=𝑐_𝑖 where 𝑐_𝑖 is the 𝑖th row of the encrypted matrix 𝐶

 (7) if 𝑚<𝑁_ent, set remaining 𝑁_ent−𝑚 entries of 𝐻 to random values