Quantum key distribution
ID: quantum-key-distribution
Quantum key distribution uses a quantum channel and an authenticated public classical channel to establish matching random keys for two parties while limiting an eavesdropper's information. The public transcript is included in the adversary's information. In an ideal successful protocol, a key of length is uniform and independent of that information. Actual protocols allow small disagreement and secrecy errors and may abort. Measurement in quantum mechanics disturbance provides parameter tests, while privacy amplification removes residual knowledge after classical reconciliation. The BB84 protocol and entanglement-based protocols are examples.
Quantum Key Distribution (QKD) is a secure communication method that leverages the principles of quantum mechanics to enable two parties to share a secret key for encryption purposes. The idea behind QKD is to utilize quantum properties, such as superposition and entanglement, to ensure that the key can be exchanged safely, even in the presence of a potential eavesdropper.
Man-in-the-middle attack
quantumcomputing.stackexchange.com/questions/142/advantage-of-quantum-key-distribution-over-post-quantum-cryptography/25727#25727 Advantage of quantum key distribution over post-quantum cryptography has Ciro Santilli's comparison to classical encryption.
Long story short:
- QKD allows you to generate shared keys without public-key cryptography. You can then use thses shared keys
- QKD requires authentication on a classical channel, exactly like a classical public-key cryptography forward secrecy would. The simplest way to do this is a with a pre-shared key, just like in classical public key cryptography. If that key is compromised at any point, your future messages can get man-in-the-middle'd, exactly like in classical cryptography.
QKD uses quantum mechanics stuff to allow sharing unsnoopable keys: you can detect any snooping and abort communication. Unsnoopability is guaranteed by the known laws of physics, up only to engineering imperfections.
Furthermore, it allows this key distribution without having to physically take a box by car somewhere: once the channel is established, e.g. optical fiber, you can just keep generating perfect keys from it. Otherwise it would be pointless, as you could just drive your one-time pad key every time.
However, the keys likely have a limited rate of generation, so you can't just one-time pad the entire message, except for small text messages. What you would then do is to use the shared key with symmetric encryption.
Therefore, this setup usually ultimately relies on the idea that we believe that symmetric encryption is safer than , even though there aren't mathematical safety proofs of either as of 2020.
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