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arXiv 2402.11533cs.ITmath.IT
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达到容量的列表可译码的随机性高效构造

Randomness-Efficient Constructions of Capacity-Achieving List-Decodable Codes

Jonathan Mosheiff, Nicolas Resch, Kuo Shang, Chen Yuan

AI总结:

该研究提出两种代数构造方法,以更少的随机比特生成达到Elias界的列表可译码,其对偶码性质良好且支持拟线性编码,并证明了近似RLC的证明策略存在随机性下界。

摘要:

我们希望使用尽可能少的随机比特,在小字母表上生成列表可译码。具体而言,我们希望生成达到我们所称的Elias界的码,即它们是$(ρ,L)$-列表可译码,且码率$R \geq 1-h(ρ)-O(1/L)$。长期以来的研究表明,均匀随机线性码(RLC)能够达到Elias界:因此我们知道$O(n^2)$随机比特就足够了。此前的研究通过对低偏差码进行删余,证明仅需$O(Ln)$随机比特即可。这些近期的构造是组合式的。\n我们提出了两种新的代数构造方法。与此前的工作相比,我们的构造更简单、更直接。此外,我们所设计的码的对偶码也非常易于分析。我们的第一种构造——可视为Wozencraft系综的推广——达到了Elias界,且消耗$Ln$随机比特。此外,其对偶码以高概率达到GV界,并且原码和对偶码都支持拟线性时间编码算法。第二种构造消耗$2nL$随机比特,生成的码及其对偶码都能达到Elias界。正如我们所讨论的,对偶码的性质对于密码学应用通常至关重要。\n在上述所有情况中——包括此前达到$O(Ln)$随机性复杂度的工作——这些码都被设计为“近似”随机线性码(RLC)。也就是说,对于给定的局部性参数$L$,我们构造出与RLC具有相同$L$-局部性质的码。这使得人们可以借助已知的RLC列表可译码性结果,从而推断出近似RLC的码也能达到Elias界。作为最后一项贡献,我们指出这种证明策略本质上无法在随机比特少于$L(1-R)n\log_2(q)$的情况下,生成$\mathbb F_q$上码率为$R$的列表可译码。

英文摘要:

We wish to generate list-decodable codes over small alphabets using as little randomness as possible. Specifically, we hope to generate codes achieving what we term the Elias bound, which means that they are $(ρ,L)$-list-decodable with rate $R \geq 1-h(ρ)-O(1/L)$. A long line of work shows that uniformly random linear codes (RLCs) achieve the Elias bound: hence, we know $O(n^2)$ random bits suffice. Prior works demonstrate that just $O(Ln)$ random bits suffice, via puncturing of low-bias codes. These recent constructions are combinatorial. We provide two new constructions, which are algebraic. Compared to prior works, our constructions are simpler and more direct. Furthermore, our codes are designed in such a way that their duals are also quite easy to analyze. Our first construction -- which can be seen as a generalization of the Wozencraft ensemble -- achieves the Elias bound and consumes $Ln$ random bits. Additionally, its dual code achieves the GV-bound with high probability, and both the primal and dual admit quasilinear-time encoding algorithms. The second construction consumes $2nL$ random bits and yields a code where both it and its dual achieve the Elias bound. As we discuss, properties of a dual code are often crucial for applications in cryptography. In all of the above cases -- including the prior works achieving randomness complexity $O(Ln)$ -- the codes are designed to "approximate" RLCs. Namely, for a given locality parameter $L$ we construct codes achieving the same $L$-local properties as RLCs. This allows one to appeal to known list-decodability results for RLCs and thereby conclude that the code approximating an RLC also achieves the Elias bound. As a final contribution, we indicate that such a proof strategy is inherently unable to generate list-decodable codes of rate $R$ over $\mathbb F_q$ with less than $L(1-R)n\log_2(q)$ bits of randomness.

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