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Paper: Fine-tuning the ISO/IEC Standard LightMAC

Authors:
Soumya Chattopadhyay , Indian Statistical Institute, Kolkata, India
Ashwin Jha , CISPA Helmholtz Center for Information Security, Saarbr├╝cken, Germany
Mridul Nandi , Indian Statistical Institute, Kolkata, India
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Conference: ASIACRYPT 2021
Abstract: LightMAC, by Luykx et al., is a block cipher based message authentication code (MAC). The simplicity of design and low overhead allows it to have very compact implementations. As a result, it has been recently chosen as an ISO/IEC standard MAC for lightweight applications. LightMAC has been shown to achieve query-length independent security bound of $O(q^2/2^n)$ when instantiated with two independently keyed $n$-bit block ciphers, where $q$ denotes the number of MAC queries and the query-length is upper bounded by $(n-s)2^s$ bits for a fixed counter size $s$. In this paper, we aim to minimize the number of block cipher keys in LightMAC. First, we show that the original LightMAC instantiated with a single block cipher key, referred as 1k-LightMAC, achieves security bound of $O(q^2/2^n)$ while the query-length is at least $(n-s)$ bits and at most $(n-s)\min\{2^{n/4},2^s\}$ bits. Second, we show that a minor variant of 1k-LightMAC, dubbed as LightMAC-ds, achieves security bound of $O(q^2/2^n)$ while query-length is upper bounded by $(n-s)2^{s-1}$ bits. Of independent interest, our security proof of 1k-LightMAC employs a novel sampling approach, called the reset-sampling, as a subroutine within the H-coefficient proof setup.
BibTeX
@inproceedings{asiacrypt-2021-31493,
  title={Fine-tuning the ISO/IEC Standard LightMAC},
  publisher={Springer-Verlag},
  author={Soumya Chattopadhyay and Ashwin Jha and Mridul Nandi},
  year=2021
}