Indifferentiability of the Sponge Construction with a Restricted Number of Message Blocks

Authors

  • Charlotte Lefevre Digital Security Group, Radboud University, Nijmegen, The Netherlands

DOI:

https://doi.org/10.46586/tosc.v2023.i1.224-243

Keywords:

sponge, lightweight cryptography, indifferentiability

Abstract

The sponge construction is a popular method for hashing. Quickly after its introduction, the sponge was proven to be tightly indifferentiable from a random oracle up to ≈ 2c/2 queries, where c is the capacity. However, this bound is not tight when the number of message blocks absorbed is restricted to ℓ < ⌈ c / 2(bc) ⌉ + 1 (but still an arbitrary number of blocks can be squeezed). In this work, we show that this restriction leads to indifferentiability from a random oracle up to ≈ min { 2b/2, max { 2c/2, 2b−ℓ×(bc) }} queries, where b > c is the permutation size. Depending on the parameters chosen, this result allows to have enhanced security or to absorb at a larger rate for applications that require a fixed-length input hash function.

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Published

2023-03-10

Issue

Section

Articles

How to Cite

Indifferentiability of the Sponge Construction with a Restricted Number of Message Blocks. (2023). IACR Transactions on Symmetric Cryptology, 2023(1), 224-243. https://doi.org/10.46586/tosc.v2023.i1.224-243