self-sifting-qkd-protocol

# Self-Sifting QKD Protocol From arXiv:2606.27299 ## Protocol Design Two-way QKD using maximally entangled Bell state: 1. Alice and Bob share one qubit of Bell pair as quantum channel 2. Alice applies scrambling operator (security mechanism) 3. Traveling qubit does NOT directly encode key information 4. All sifting and eavesdropper detection done exclusively by Bob 5. Control mode never publicly announced ## Security Advantages - Mode-dependent attacks prevented (control mode not announced) - Traveling qubit attacks limited (no direct key encoding) - Normally discarded rounds used for eavesdropper detection - Ancilla-based attacks detectable in most general form ## Attack Detection Analyzes broad class of ancilla-based attacks where Eve couples ancillary system to transmitted qubit. All such attacks detectable. ## Implementation Pattern ``` Bell State -> [Alice: Scramble] -> [Channel] -> [Bob: Detect + Sift + Key Extract] (no key info) (all processing) ``` ## When to Use - Designing two-way QKD protocols - Analyzing quantum channel security against ancilla attacks - Scenarios where public sifting announcements are risky - Long-distance quantum communication requiring robust eavesdropper detection