Matej Pivoluska

Weak randomness seriously limits the security of quantum key distribution

In usual security proofs of quantum protocols the adversary (Eve) is expected to have full control over any quantum communication between any communicating parties (Alice and Bob). Eve is also expected to have full access to an authenticated classical channel between Alice and Bob. Unconditional security against any attack by Eve can be proved even in the realistic setting of device and channel imperfection. In this Letter we show that the security of QKD protocols is ruined if one allows Eve to possess a very limited access to the random sources used by Alice. Such knowledge should always be expected in realistic experimental conditions via different side channels.

Device-independent randomness extraction for arbitrarily weak min-entropy source

In this paper we design a protocol to extract random bits with an arbitrarily low bias from a single arbitrarily weak min-entropy block source in a device independent setting. The protocol employs Mermin devices that exhibit super-classical correlations. Number of devices used scales polynomially in the length of the block n, containing entropy of at least two bits. Our protocol is robust, it can tolerate devices that malfunction with a probability dropping polynomially in n at the cost of constant increase of the number of devices used.

Device-independent randomness extraction from an arbitrarily weak min-entropy source

Expansion and amplification of weak randomness play a crucial role in many security protocols. Using quantum devices, such procedure is possible even without trusting the devices used, by utilizing correlations between outcomes of parts of the devices. We show here how to extract random bits with an arbitrarily low bias from single arbitrarily weak min-entropy block source in a device independent setting. To do this we use Mermin devices that exhibit super-classical correlations. The number of devices used scales polynomially in the length of the random sequence n. Our protocol is robust, it can tolerate devices that malfunction with probability decreasing polynomially in n at the cost of minor increase in the number of devices used.

An explicit classical strategy for winning a game

A

Measurements in two bases are sufficient for certifying high-dimensional entanglement

\mathrm{CHSH}_{q}

Tight bound on the classical value of generalized Clauser-Horne-Shimony-Holt games

game is a generalization of the standard two player

Loss of information in quantum guessing game

\mathrm{CHSH}

1-out-of-2 oblivious transfer using a flawed bit-string quantum protocol

game, having

Device-independent Randomness Extraction for Arbitrarily Weak Min-entropy Source

q

Single Min-Entropy Random Source can be Amplified

different input and output options. In contrast to the binary game, the best classical and quantum winning strategies are not known exactly. In this paper we provide a constructive classical strategy for winning a