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Bennett et Brassard BB84

We are illustrating the Public Key Distribution Protocol that Bennett and Brassard imagined in 1984.
It consists in an exchange of qubits between Alice and Bob. Eve is likely a spy.

You can test the tool by opening the windows. Each represents one of the 3 protagonists.
It is possible to run each window on the same machine or on any computer connected to the web:
The main thing is to work on the same "group" (cf. below).
     
1. ALICE

By clicking on this image, you can open Alice's window.
To sign into the protocol, you must enter a group name, which will be the same for Eve and Bob.
Note: Avoid names like "test" that will lead you to probably an existing group. ;)

Then click on "OK".
You can see |0> and |1> expressed in two different bases.
To send any qubit to Bob, you only have to drag and drop it to the entrance of the big arrow...
A new qubit arrives in the previous place of the qubit you sent. 		 
2. EVE

Whenever Alice sends qubits, they first pass into the channel of Eve who can decide to spy or not.

To spy, you can measure the qubit in one of the two bases, by selecting the graphic object corresponding to the operator.
You just have to put this object near the unknown qubit on the right. This collapses the qubit on | 0> or | 1> in the chosen base.
Afterwards, the qubit is sent back again to Bob.

If you do not want to spy, just take the qubit and drag it to the entrance of the arrow...
  
3. BOB

You can measure the qubit that comes from Eve in a base or the other, by selecting the graphic object corresponding to the operator.
You just have to put this object near the unknown qubit on the right. This collapses the qubit on | 0> or | 1> in the chosen base.
Then the qubit disappears.

It is not necessary to notice the result because you always can access the summary.
  
4. SUMMARY

By clicking on the button "summary", Alice and Bob can see at any moment the exchanges and decide which qubits they keep.
The summary displays the qubits read by Eve. It also highlights the cases where Eve was hidden.
  


For more details on BB84 :

http://researchweb.watson.ibm.com/people/b/bennetc/bennettc198469790513.pdf
http://hal.archives-ouvertes.fr/docs/00/09/29/55/PDF/cel-29.pdf