We consider a collision search problem (CSP), where given a parameter C, the goal is to find C collision pairs in a random function (Formula presented) (where (Formula presented) using S bits of memory. Algorithms for CSP have numerous cryptanalytic applications such as space-efficient attacks on double and triple encryption. The best known algorithm for CSP is parallel collision search (PCS) published by van Oorschot and Wiener, which achieves the time-space tradeoff (Formula presented). In this paper, we prove that any algorithm for CSP satisfies (Formula presented), hence the best known time-space tradeoff is optimal (up to poly-logarithmic factors in N). On the other hand, we give strong evidence that proving similar unconditional time-space tradeoff lower bounds on CSP applications (such as breaking double and triple encryption) may be very difficult, and would imply a breakthrough in complexity theory. Hence, we propose a new restricted model of computation and prove that under this model, the best known time-space tradeoff attack on double encryption is optimal.
CITATION STYLE
Dinur, I. (2020). Tight time-space lower bounds for finding multiple collision pairs and their applications. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 12105 LNCS, pp. 405–434). Springer. https://doi.org/10.1007/978-3-030-45721-1_15
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