Temporary assumptions - quantum and classical

Long-term security is achieved by protocols which use computational assumptions only during the execution of the protocol and become information theoretically secure afterwards. Coin flipping protocols and zero knowledge arguments are examples for protocols achieving long-term security. In this work we consider this regime between computational security and information theoretic security. A security model for long-term security is sketched and the class K of all two argument functions which can be computed with long-term security is characterised. Furthermore it is shown that the class Q of all two argument functions which can be computed using quantum cryptography is strictly contained in K. The characterisation of K is a generalisation of a result of Kushilevitz (1992), where he characterises the two argument functions which can securely be computed in presence of an unbounded passive adversary. The result in the quantum case additionally relies on the impossibility results of (D. Mayers, 1997) , (H.-K. Lo and H. R Chau, 1996) and the impossibility of quantum coin flipping result of Kitaev which is published in (A. Ambainis et al., 2004)