Reference
Glossary
Forty terms used across the site.
- Authentication (classical channel)
- Verifying the source and integrity of classical messages in QKD, usually with Wegman–Carter MACs.
- B92
- Two-state QKD protocol of Bennett (1992).
- BB84
- Four-state, two-basis QKD protocol of Bennett and Brassard (1984).
- Bell state
- One of four maximally entangled two-qubit states.
- Bell-state measurement (BSM)
- Joint measurement projecting two qubits onto the Bell basis; used in teleportation, swapping and MDI-QKD.
- Bit commitment
- Protocol to commit to a bit that is both hidden and binding.
- CHSH
- Bell inequality with local bound 2 and quantum bound $2\sqrt2$.
- Composable security
- Security of a key that persists when used in other protocols, quantified by $\varepsilon$.
- CV-QKD
- Continuous-variable QKD using coherent states and homodyne detection.
- Decoy state
- Pulses of different intensities used to detect PNS attacks.
- Device-independent (DI)
- Security derived from observed Bell violation without trusting devices.
- E91
- Ekert’s entanglement-based QKD protocol (1991).
- Entanglement swapping
- Creating entanglement between two systems by Bell-measuring their partners.
- Hong–Ou–Mandel effect
- Two identical photons on a beam splitter exit together.
- Holevo bound
- Upper limit on classical information extractable from quantum states.
- Information reconciliation
- Classical error correction of the sifted key (e.g. Cascade, LDPC).
- Lattice
- Regular grid of points; hard lattice problems underlie ML-KEM and ML-DSA.
- LWE / Module-LWE
- Learning-with-errors problem; basis of lattice cryptography.
- MDI-QKD
- QKD with an untrusted measurement relay.
- ML-DSA
- NIST FIPS 204 lattice signature scheme (Dilithium).
- ML-KEM
- NIST FIPS 203 lattice key-encapsulation mechanism (Kyber).
- No-cloning theorem
- Unknown quantum states cannot be perfectly copied.
- One-time pad
- Encryption with a random key as long as the message, used once; perfectly secret.
- PLOB bound
- Repeaterless secret-key capacity $-\log_2(1-\eta)$ of a pure-loss channel.
- PNS attack
- Photon-number-splitting attack on multi-photon pulses.
- Post-quantum cryptography
- Classical algorithms believed secure against quantum computers.
- Privacy amplification
- Hashing to shorten a key and remove Eve’s partial information.
- QBER
- Quantum bit error rate of the sifted key.
- Quantum memory
- Device that stores a quantum state for later retrieval.
- Quantum repeater
- Node that extends entanglement distribution using swapping, memories and purification.
- QRNG
- Quantum random number generator.
- SARG04
- BB84-state protocol with sifting that resists PNS attacks.
- Shor’s algorithm
- Quantum algorithm for factoring and discrete logarithms.
- Sifting
- Discarding positions where bases differ.
- SLH-DSA
- NIST FIPS 205 hash-based signature (SPHINCS+).
- SNSPD
- Superconducting nanowire single-photon detector.
- SPDC
- Spontaneous parametric down-conversion, a source of photon pairs.
- Teleportation
- Transferring an unknown qubit using entanglement and two classical bits.
- TF-QKD
- Twin-field QKD with $\sqrt\eta$ rate scaling.
- Trusted relay
- Intermediate node trusted with key material in a QKD network.
- Universal hashing
- Family of hash functions used for authentication and privacy amplification.