self-sifting-qkd-protocol

name	self-sifting-qkd-protocol
description	Self-Sifting Quantum Key Distribution protocol using two-way entangled Bell state qubits with scrambling operator security. All sifting and eavesdropper detection postponed to Bob. Use when designing QKD protocols, quantum communication security, or analyzing ancilla-based attacks on quantum channels.

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