Mitigating collision and preimage attacks against the generalized MDC-2 mode of operation

This paper proposes a set of mechanisms for enhancing the security of the generalized MDC-2 mode of operation. The MDC-2 mode is used for constructing a double length hash function, using block cipher building blocks, and is believed to provide some collision resistance. Recently, several attacks on MDC-2 have been published - collision, first and second pre-image attacks, with complexity below the ideal. In this paper we analyze the root-cause of these attacks, as applied to the generalized MDC-2 mode, and propose techniques for mitigating them. By mitigating we mean that with our amendments the attacks are either not applicable, or their complexity is pushed to ideal.