Cryptology ePrint Archive: Report 2020/1344

Indifferentiability of SKINNY-HASH Internal Functions

Akinori Hosoyamada and Tetsu Iwata

Abstract: We provide a formal proof for the indifferentiability of SKINNY-HASH internal function from a random oracle. SKINNY-HASH is a family of function-based sponge hash functions, and it was selected as one of the second round candidates of the NIST lightweight cryptography competition. Its internal function is constructed from the tweakable block cipher SKINNY. The construction of the internal function is very simple and the designers claim $n$-bit security, where $n$ is the block length of SKINNY. However, a formal security proof of this claim is not given in the original specification of SKINNY-HASH. In this paper, we formally prove that the internal function of SKINNY-HASH has $n$-bit security, i.e., it is indifferentiable from a random oracle up to $O(2^n)$ queries, substantiating the security claim of the designers.

Category / Keywords: secret-key cryptography / provable security, sponge construction, indifferentiability, SKINNY, SKINNY-HASH

Date: received 26 Oct 2020, last revised 1 Nov 2020

Contact author: akinori hosoyamada bh at hco ntt co jp,hosoyamada akinori@nagoya-u jp,tetsu iwata@nagoya-u jp

Available format(s): PDF | BibTeX Citation

Note: Minor revision: Some information on related works is added.

Version: 20201102:024731 (All versions of this report)

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