Abstract

All existing quantum cryptosystems use non-orthogonal states as the carriers of information. Non-orthogonal states cannot be cloned (duplicated) by an eavesdropper. In result, any eavesdropping attempt must introduce errors in the transmission, and therefore, can be detected by the legal users of the communication channel. Orthogonal states are not used in quantum cryptography, since they can be faithfully cloned without altering the transmitted data. In this Letter we present a cryptographic scheme based on orthogonal states, which also assures the detection of any eavesdropper. 1 A basic task in cryptography is exchanging a secret message between two users, traditionally called Alice and Bob, in a way that no other party can read it. The only known method to do this in a proven secure way is to use a ‘one-time pad’, which uses a previously shared secret information called a key. The key, a sequence of random bits, is used for encrypting the message. The encrypted message is completely confidential, even if transmitted via a public communication channel. Thus, the security of any key-based

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