Curriculum / Quantum Cryptography / Quantum Cryptography Capstone
Quantum Cryptography Capstone
Build a complete quantum-secure communication system with QKD and post-quantum fallback.
Quantum Cryptography Capstone
Build a complete quantum-secure communication system that demonstrates the key components from this track. You will implement four checkpoints, each adding a layer to the security stack.
System Overview
You are building Alice and Bob's end-to-end quantum-secure messaging system:
- 1.Checkpoint 1: BB84 QKD, Simulate the BB84 key distribution protocol and extract a sifted key
- 2.Checkpoint 2: Privacy Amplification, Compress the sifted key using a hash function to eliminate any partial information Eve may hold
- 3.Checkpoint 3: OTP Encryption, Encrypt and decrypt a secret message using the quantum-generated key
- 4.Checkpoint 4: Eavesdropping Detection, Simulate Eve's intercept-resend attack and show that it increases the QBER above the detection threshold
What You'll Demonstrate
When complete, your system will show:
- •BB84 produces a sifted key where matching-basis rounds agree
- •Privacy amplification produces a final key of appropriate length
- •OTP encryption with the quantum key produces an unreadable ciphertext
- •Eve's intercept-resend attack produces QBER near 25%, triggering abort
This integrates quantum physics (qubits, superposition, measurement), classical cryptography (XOR, hash functions), and protocol engineering (QBER threshold, privacy amplification) into a single working system.
Technical Requirements
- •N_QUBITS = 100: number of qubits Alice sends
- •DETECTION_SAMPLE = 20: bits compared for eavesdropping detection
- •PRIVACY_AMP_BITS = 16: final key length after privacy amplification
- •QBER threshold: abort if QBER > 0.11 (11%)
- •All quantum operations use the provided helper functions
This capstone demonstrates the only known end-to-end information-theoretically secure communication system: QKD for key distribution + OTP for encryption. Neither component alone provides full security, OTP needs secure key distribution; QKD provides keys but not encryption. Together they achieve unconditional security from physics, not computational hardness.
How this lesson works
A multi-step project that combines several concepts into one larger build, checked checkpoint by checkpoint as you go.
Part of: Quantum Cryptography
Master quantum key distribution, the threat quantum computers pose to classical cryptography, and post-quantum cryptographic standards.
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