Lab 03 · Applied cryptography · 30–40 minutes
PQC: The Size of Security
Quantum-resistant keys still travel on ordinary networks. Explore the bytes behind secure connections and signed messages.
Published sizes and a transmission model, not a live speed benchmark.
Quantum-resistant does not mean quantum-powered
Labs 1 and 2 explored what quantum algorithms could do to today's cryptography. Post-quantum cryptography, or PQC, is the response: new cryptographic methods designed to resist known classical and quantum attacks. They run on ordinary computers. You do not need a quantum computer to use them.
Agree on a secret: ML-KEM
Alice shares a public key. Bob uses it to create a shared secret and a small package called a ciphertext. Alice uses her private key and that ciphertext to recover the same secret. Both can then use a symmetric cipher such as AES to protect their conversation.
The KEM ciphertext is not the encrypted conversation. It is part of establishing the secret.
Verify a sender: ML-DSA
Alice signs a document with her private key. Bob checks the signature with Alice's public key. A valid signature helps detect changes and verify the signer, provided the public key really belongs to Alice.
Signing does not hide the document. Confidentiality and authenticity are different jobs.
The network still has to carry the bytes
A byte is eight bits of data. Public keys, ciphertexts, and signatures are stored as bytes. PQC objects can be larger than familiar classical alternatives, so even correct cryptography can strain small messages, slow links, or older equipment.
Imagine shipping a package: its size, the truck's capacity, and the road's speed are separate questions. Here, the package is cryptographic data, the capacity is a chosen chunk budget, and the road speed is bandwidth.
Predict before experimenting
If you double the link speed, does the key shrink? If the recipient already has a trusted public key, what can you stop sending? Compare two runs and explain what changed.