Paper 2016/851

A New Algorithm for the Unbalanced Meet-in-the-Middle Problem

Ivica Nikolic and Yu Sasaki


A collision search for a pair of $n$-bit unbalanced functions (one is $R$ times more expensive than the other) is an instance of the meet-in-the-middle problem, solved with the familiar standard algorithm that follows the tradeoff $TM=N$, where $T$ and $M$ are time and memory complexities and $N=2^n$. By combining two ideas, unbalanced interleaving and Oorschot-Wiener parallel collision search, we construct an alternative algorithm that follows $T^2 M = R^2 N$, where $M\le R$. Among others, the algorithm solves the well-known open problem: how to reduce the memory of unbalanced collision search.

Available format(s)
Publication info
Published by the IACR in ASIACRYPT 2016
meet-in-the-middletradeoffcollision search
Contact author(s)
inikolic @ ntu edu sg
sasaki yu @ lab ntt co jp
cube444 @ gmail com
2016-09-07: received
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Creative Commons Attribution


      author = {Ivica Nikolic and Yu Sasaki},
      title = {A New Algorithm for the Unbalanced Meet-in-the-Middle Problem},
      howpublished = {Cryptology ePrint Archive, Paper 2016/851},
      year = {2016},
      note = {\url{}},
      url = {}
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