18、针对安全 CKWS 方案的被动查询恢复攻击

针对安全 CKWS 方案的被动查询恢复攻击

1. CKWS 适配的精炼分数攻击算法

CKWS 适配的精炼分数攻击算法旨在预测陷门对应的关键字组合。以下是该算法的具体实现：

Algorithm 1: CKWS - adapted refined score attack.
Input: Ksimilar, Csckw, Q, Cstd, KnownQ, RefSpeed
Result: List of keyword conjunctions as predictions for trapdoors with certainty
final_pred ← [];
unknownQ ← Q;
while unknownQ ≠ ∅ do
    // Set remaining unknown queries.
    unknownQ ← {td : (td ∈ Q) ∧ (¬∃ckw ∈ Ksimilar : (td, ckw) ∈ KnownQ)};
    temp_pred ← [];
    // Propose a prediction for each unknown query.
    forall td ∈ unknownQ do
        cand ← [];
        forall ckw ∈ Ksimilar do
            s ← -ln(||Csckw[ckw] - Cstd[td]||);
            Append {"kw": ckw, "score": s } to cand;
        end
        Sort cand in descending or