Has subquantum crypto attack been substantiated? arXiv:quant-ph/0203049v2 12 Apr 2002 Subquantum Information and Computation Antony Valentini It is argued that immense physical resources – for nonlocal communication, espionage, and exponentially-fast computation – are hidden from us by quantum noise, and that this noise is not fundamental but merely a property of an equilibrium state in which the universe happens to be at the present time. It is suggested that ‘non-quantum’ or nonequilibrium matter might exist today in the form of relic particles from the early universe. We describe how such matter could be detected and put to practical use. Nonequilibrium matter could be used to send instantaneous signals, to violate the uncertainty principle, to distinguish non-orthogonal quantum states without disturbing them, to eavesdrop on quantum key distribution, and to outpace quantum computation (solving NP-complete problems in polynomial time). ... 6 Eavesdropping on Quantum Key Distribution Alice and Bob want to share a secret sequence of bits that will be used as a key for cryptography. During distribution of the key between them, they must be able to detect any eavesdropping by Eve. Three protocols for quantum key distribution – BB84 [20], B92 [21], and E91 (or EPR) [22] – are known to be secure against classical or quantum attacks (that is, against eavesdropping based on classical or quantum physics) [23]. But these protocols are not secure against a ‘subquantum’ attack [7]. ... E91 is particularly interesting for it relies on the completeness of quantum theory – that is, on the assumption that there are no hidden ‘elements of reality’. Pairs of spin-1/2 particles in the singlet state are shared by Alice and Bob, who perform spin measurements along random axes. For coincident axes the same bit sequence is generated at each wing, by apparently random quantum outcomes. ‘The eavesdropper cannot elicit any information from the particles while in transit ..... because there is no information encoded there’ [22]. But our Eve has access to information outside the domain of quantum theory. She can measure the particle positions while in transit, without disturbing the wavefunction, and so predict the outcomes of spin measurements at the two wings (for the publicly announced axes).12 Thus Eve is able to predict the key shared by Alice and Bob.