A long standing open question is whether the distinguisher of high rate alternant codes or Goppa codes \cite{FGOPT11} can be turned into an algorithm recovering the algebraic structure of such codes from the mere knowledge of an arbitrary generator matrix of it. This would allow to break the McEliece scheme as soon as the code rate is large enough and would break all instances of the CFS signature scheme. We give for the first time a positive answer for this problem when the code is {\em a generic alternant code} and when the code field size $q$ is small : $q \in \{2,3\}$ and for {\em all} regime of other parameters for which the aforementioned distinguisher works. This breakthrough has been obtained by two different ingredients : (i) a way of using code shortening and the component-wise product of codes to derive from the original alternant code a sequence of alternant codes of decreasing degree up to getting an alternant code of degree $3$ (with a multiplier and support related to those of the original alternant code); (ii) an original Gr\"obner basis approach which takes into account the non standard constraints on the multiplier and support of an alternant code which recovers in polynomial time the relevant algebraic structure of an alternant code of degree $3$ from the mere knowledge of a basis for it.

翻译：一个长期悬而未决的问题是：高码率交替码或Goppa码的区分器 \cite{FGOPT11} 能否转化为一种算法，仅通过该码的任意生成矩阵知识便恢复其代数结构。这将使得只要码率足够大就能破解McEliece方案，并摧毁CFS签名方案的所有实例。我们首次对该问题给出了肯定回答，条件是码为{\em 一般交替码}，且码域大小$q$较小：$q \in \{2,3\}$，并针对前述区分器有效的{\em 所有}其他参数范围。这一突破通过两种不同的要素实现：(i) 利用码缩短和逐分量乘积，从原始交替码导出一系列度数递减的交替码，直至得到度数为$3$的交替码（其乘子与支撑与原始交替码相关）；(ii) 一种原创的Gröbner基方法，该方法考虑了交替码乘子与支撑的非标准约束，仅通过其基的知识即可在多项式时间内恢复度数为$3$的交替码的相关代数结构。