Query-Biased Preview over Outsourced and Encrypted Data

Algorithm 4

SecQBP algorithm.

𝙶𝚎𝚗1^𝑘:

 (1) sample index keys 𝐾_𝑚,𝐾_𝑝←_𝑈{0,1}^𝑘, generate document

    encryption key 𝐾_𝑑←𝙴𝚂.𝙶𝚎𝚗1^𝑘

 (2) output 𝐾=𝐾_𝑚,𝐾_𝑝,𝐾_𝑑

𝚂𝚎𝚝𝚞𝚙_𝐾(𝑑):

 (1) invoke 𝙴𝙳_𝐾𝑑(𝑑) to get 𝑒 and the encrypted document 𝐷

 (2) invoke 𝙸𝚗𝚍𝚎𝚡_{(𝐾𝑚,𝐾𝑝)}(𝑑,𝑒) to get the secure index 𝐻

 (3) output 𝐷,𝐻

𝚀𝚞𝚎𝚛𝚢_𝐾(𝐰):

 (1) for each keyword 𝑤_𝑖 in 𝐰=𝑤₁,…,𝑤_𝑛, compute 𝑡_𝑖←𝜋_𝐾𝑝𝑤_𝑖

 (2) put 𝑡₁,…,𝑡_𝑛 into query 𝑞 and pad it to length 𝑊_max

 (3) output the query 𝑞

𝙲𝚘𝚖𝚙𝚞𝚝𝚎𝚂𝚌𝚘𝚛𝚎𝑞,𝐻:

 (1) let 𝑘 represent the snippet amount, unpack 𝑞 to get the queried

    tokens 𝑡=𝑡₁,…,𝑡_𝑛, set a flag 𝐹=1

 (2) select a subset of 𝑡∶𝑡^′=𝑡^′₁,…,𝑡^′_𝑚 where 𝑡^′_𝑖 is in 𝐻. If no element

    is in 𝐻, then set 𝐹=0

 (3) create the result ℎ=𝐻𝑡^′₁⊕⋯⊕𝐻𝑡^′_𝑚 if 𝐹==1, or else randomly

    select an index 𝑖 and set ℎ=𝐻[𝑖]

 (4) put 𝑡^′ into query 𝑞^′ and pad it to length 𝑊_max

 (5) output 𝑟=ℎ,𝑞^′,𝐹,𝑘

𝙳𝚎𝚌𝚂𝚌𝚘𝚛𝚎_𝐾𝐰,𝑑,𝑟:

 (1) unpack 𝑟=ℎ,𝑞^′,𝐹,𝑘 and get 𝑡^′=𝑡^′₁,…,𝑡^′_𝑚

 (2)  if  the flag 𝐹==0   then

 (3)  randomly select an index 𝑖∈[1,𝑘]

 (4)  else

 (5) according to 𝑡^′, generate the decryption key 𝑘_𝑗←𝑓_𝐾𝑚(𝑤_𝑗∣∣𝑑)

      for each matched keyword 𝑤_𝑗 in 𝐰

 (6) compute the decryption key 𝑘_𝑟=𝑘₁⊕𝑘₂⊕⋯⊕𝑘_𝑚

 (7) invoke 𝑎←𝙳𝚎𝚌𝚘𝚍𝚎_𝑘𝑟(ℎ) using Matrix-AC

 (8) choose a snippet number 𝑖 in 𝑎 with the highest score

 (9) end if 

 (10) output the snippet index 𝑖

  𝙳𝚎𝚌𝚂𝚗𝚒𝚙_𝐾𝑑(𝐷_𝑖): output the plaintext snippet 𝐷_𝑖←𝙴𝚂.𝙳𝚎𝚌_𝐾𝑑𝐷_𝑖