Cryptology ePrint Archive: Report 2018/784

Tweakable Block Ciphers Secure Beyond the Birthday Bound in the Ideal Cipher Model

ByeongHak Lee and Jooyoung Lee

Abstract: We propose a new construction of tweakable block ciphers from standard block ciphers. Our construction, dubbed XHX2, is the cascade of two independent XHX block ciphers, so it makes two call to the underlying block cipher using tweak-dependent keys. We prove the security of XHX2 up to min{2^{2(n+m)/3},2^{n+m/2}} queries (ignoring logarithmic factors) in the ideal cipher model, when the block cipher operates on n-bit blocks using m-bit keys. The XHX2 tweakable block cipher is the first construction that achieves beyond-birthday-bound security with respect to the input size of the underlying block cipher in the ideal cipher model.

Category / Keywords: tweakale block cipher, beyond-birthday-bound security, ideal cipher model

Original Publication (in the same form): IACR-ASIACRYPT-2018

Date: received 27 Aug 2018

Contact author: lbh0307 at kaist ac kr, hicalf@kaist ac kr

Available format(s): PDF | BibTeX Citation

Version: 20180901:024147 (All versions of this report)

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