Táticas de ataque a protocolos quânticos de distribuição de chaves criptográficas utilizando estratégias de discriminação de estados

Abstract

The postulates of quantum mechanics generates conditions that garantee the security of quantum key distribution (QKD) protocols, essencials to quantum cryptography. A spy that wishes to intercept the construction of a key in a QKD protocol will not be able to discriminate between two or more quantum states with certainty if they are non-orthogonal and, besides that, she will not be able to clone the states. These physical limitations compel the spy to search for different ways of attacking the protocols. Several state-discrimination strategies were created and they can be applied in the spying of QKD. Each strategy has its own purpose that fits the necessity of whom is using them, like the minimzation of the average probability of error or to attain the the maximum confidence possible in the identification of a state. All of them, however, are not capable of perfectly identifying a state and, accordingly, when they are used as tools for spying, they will create mismatches between the keys created by the protocols. The goals of this work are twofold: firstly, study the attack of QKD protocols, as the B92 and the PBC00, using discrimination of quantum states; secondly, analyze the error rate that different strategies introduce to the keys. Considering intercept-resend attacks, one shows which strategies are more advantageous to the spy so she can remain undetected and how the users of the protocol can defend themselves