Security of quantum key distribution using two-mode squeezed states against optimal beam splitter attack

For the beam splitter attack strategy against quantum keydistribution using two-mode squeezed states, the analyticalexpression of the optimal beam splitter parameter is provided inthis paper by applying the Shannon information theory. Thetheoretical secret information rate after error correction andprivacy amplification is given in terms of the squeezed parameterand channel parameters. The results show that the two-mode squeezedstate quantum key distribution is secure against an optimal beamsplitter attack.