assumes that the polarization of photons is used as a carrier of information, so Alice defines a random key with a length Q and uses a randomly selected polarization from the alphabet as a carrier of the key.
In figure 1 we can see that at low qudit dimension (up to d ~ 16) the protocol's security against noncoherent attack is higher when d+1 bases are used (when d = 2 it corresponds as noted above to greater security of six-state protocol than BB84 protocol).
An eavesdropper can obtain more information about the encryption key in the B92 protocol than in the BB84 protocol for the given error level, however.
In practice for realisation of BB84 and six-state protocols weak coherent pulses with average photon number about 0.
The next three stages of the protocol, common to both BB84 and B92, are conducted over an unsecured public link (called the classical channel, since this can be standard IP communications).
Figure 4 shows a schematic diagram of our fiber-based BB84 QKD system, which uses a pair of our PCBs to process the data at a continuous high data rate (13) to create a shared sifted key according to the BB84 protocol.
This process separates the photons into four paths, corresponding to the four BB84 encoding states.
For brevity, we will consider the well-known scheme BB84.
BB84 protocol was proposed by Bennett and Brassard .
In contrast to the BB84 protocol, which estimates a single error rate, two error rates [e.
To implement the BB84 algorithm we chose for photon polarization the rectilinear (R) and diagonal (D) bases and the convention from Table I to represent the bits from the key.
The steps of the BB84 quantum key distribution algorithm are: