BB84 Quest 🧪🔑

In quantum communication, Alice and Bob need to share a secret key to encrypt messages (using a one-time pad). The challenge is creating that key securely over a channel that might be watched.

One famous way to do this is the BB84 protocol. Alice randomly chooses a basis (➕ or ×) and a bit (0 or 1), encodes it into a qubit, and sends it to Bob.

Bob also randomly chooses a basis and measures the qubit. Later, Alice and Bob publicly compare only which bases they used. If the bases match, they keep the bit; if not, they discard it. The kept bits form the secret key.

If an eavesdropper (Eve) tries to intercept, she must guess a basis. Guessing wrong disturbs the qubit, creating errors. That means Alice and Bob can detect her.

At the end, they compare a small random sample of their kept bits. Too many mismatches means someone interfered, so they throw the key away and restart.

You are Alice. Choose a basis and a bit, send photons to Bob, and see if you can build a secure key—or detect an attack.