Dense-Coding Attack on Three-Party Quantum Key Distribution Protocols

Cryptanalysis is an important branch in the study of cryptography, including both the classical cryptography and the quantum one. In this paper we analyze the security of two three-party quantum key distribution protocols (QKDPs) proposed recently, and point out that they are susceptible to a simple and effective attack, i.e. the dense-coding attack. It is shown that the eavesdropper Eve can totally obtain the session key by sending entangled qubits as the fake signal to Alice and performing collective measurements after Alice's encoding. The attack process is just like a dense-coding communication between Eve and Alice, where a special measurement basis is employed. Furthermore, this attack does not introduce any errors to the transmitted information and consequently will not be discovered by Alice and Bob. The attack strategy is described in detail and a proof for its correctness is given. At last, the root of this insecurity and a possible way to improve these protocols are discussed.Comment: 6 pages, 3 figure

Quantum authentication of classical messages

Although key distribution is arguably the most studied context on which to apply quantum cryptographic techniques, message authentication, i.e., certifying the identity of the message originator and the integrity of the message sent, can also benefit from the use of quantum resources. Classically, message authentication can be performed by techniques based on hash functions. However, the security of the resulting protocols depends on the selection of appropriate hash functions, and on the use of long authentication keys. In this paper we propose a quantum authentication procedure that, making use of just one qubit as the authentication key, allows the authentication of binary classical messages in a secure manner.Comment: LaTeX, 6 page

On the optimality of individual entangling-probe attacks against BB84 quantum key distribution

It is shown that an existing method to study ideal individual attacks on the BB84 QKD protocol using error discard can be adapted to reconciliation with error correction, and that an optimal attack can be explicitly found. Moreover, this attack fills Luetkenhaus bound, independently of whether error positions are leaked to Eve, proving that it is tight. In addition, we clarify why the existence of such optimal attacks is not in contradiction with the established ``old-style'' theory of BB84 individual attacks, as incorrectly suggested recently in a news feature.Comment: 12 pages, 3 figure