Black-Box Composition Does Not Imply Adaptive Security

In trying to provide formal evidence that composition has security increasing properties, we ask if the composition of non-adaptively secure permutation generators necessarily produces adaptively secure generators. We show the existence of oracles relative to which there are nonadaptively secure permutation generators, but where the composition of such generators fail to achieve security against adaptive adversaries. Thus, any proof of security for such a construction would need to be non-relativizing. This result can be used to partially justify the lack of formal evidence we have that composition increases security, even though it is a belief shared by many cryptographers. Key words: Pseudo-Randomness, Function Generators, Composition, XOR, Adaptive/Non-Adaptive Security, Oracle Separation.

• Type: Conference
• Year: 2004
• Where: EUROCRYPT
• Authors: Steven Myers
• Keywords: Cryptography, EUROCRYPT 2004, Formal Evidence, Secure Permutation Generators, Security Increasing Properties