Qiskit QKD Lab

cryptography
ecosystem-member
A BB84 QKD protocol simulator built directly on Qiskit primitives
Published

August 8, 2026

STATUS · Qiskit Ecosystem Member · Application · MIT license · on PyPI (v0.2.0)

What it does

A BB84 quantum key distribution simulator where the eavesdropper is real circuit structure, not a shortcut. Eve’s intercept-resend attack is implemented as genuine mid-circuit measurement, reset, and conditional re-preparation — the same circuits run unchanged on AerSimulator or on real IBM Quantum hardware.

pip install qiskit-qkd-lab

Requires Qiskit 2.0 or later.

from qiskit_qkd_lab.protocols import bb84
from qiskit_qkd_lab.channel.eavesdrop import InterceptResend
from qiskit_qkd_lab.diagnostics.qber import estimate_qber, key_rate_report

examples/demo_bb84.py is self-contained and prints a QBER report for clean, fully-intercepted, and partially-intercepted channels. Full API reference and a runnable end-to-end example live in docs/api.md.

Important: not a secure key yet

Reconciliation and privacy amplification aren’t implemented. The “final key” this package produces today is a sifted, QBER-estimated bit string — not a cryptographically secure key. It’s a faithful simulator of BB84’s quantum layer and QBER-based eavesdropping detection, useful for teaching and prototyping. Treat it accordingly until those pieces land.

Status

Implemented:

  • BB84 prepare/measure circuits (Z/X basis)
  • Intercept-resend eavesdropper, circuit-level (mid-circuit measurement)
  • Sifting
  • QBER estimation via public sample comparison
  • Basic key-rate / Eve-detection report
  • Test suite + CI (Python 3.10–3.13)

Not yet implemented:

  • E91 (entanglement-based) protocol
  • Beam-splitting eavesdropper
  • Cascade error reconciliation
  • Privacy amplification (universal hashing)
  • Realistic channel noise model (fiber loss, detector dark counts)
  • Live diagnostics dashboard (QBER vs. sample size, key rate vs. distance) — reusing patterns from qiskit-sqd-dashboard

Design notes

  • Eve’s classical register (eve) is entirely separate from Alice and Bob’s shared register (c) — Bob’s measurement pipeline never touches it. That separation is what makes “Eve is undetectable except through QBER” a faithful model rather than an accidental information leak in the simulation itself.
  • InterceptResend(p_intercept=...) sweeps partial interception, reproducing the textbook QBER-vs-intercept-rate curve rather than only the full-intercept extreme.
  • n_qubits in the demo represents independent single-photon sends batched into one circuit for simulation speed — no entangling gates between them — so it maps directly onto real hardware qubit-count budgets.