New Preimage Attack on MDC-4

In this paper, we provide some cryptanalytic results for double-blocklength (DBL) hash modes of block ciphers, MDC-4. Our preimage attacks follow the framework of Knudsen et al.’s time/memory tradeoff preimage attack on MDC-2. We find how to apply it to our objects. When the block length of the underlying block cipher is n bits, the most efficient preimage attack on MDC-4 requires time and space about 2, which is to be compared to the previous best known preimage attack having time complexity of 2. Additionally, we propose an enhanced version of MDC-4, MDC-4∗ based on a simple idea. It is secure against our preimage attack and previous attacks and has the same efficiency as MDC-4.