Explicit Factorization of $x^{p+1}-1$ over ${\mathbb{Z}}_{p^e}$: A Structural Approach via Dickson Polynomials

Abstract

Let $p$ be an odd prime. The factorization of the polynomial $x^{p+1}-1$ over the integer residue ring ${\mathbb{Z}}_{p^e}$ is pivotal for constructing cyclic codes with Hermitian symmetry, a critical resource for Linear Complementary Dual (LCD) codes and Entanglement-Assisted Quantum Error-Correcting Codes (EAQECC). Traditionally, lifting factorizations relies on the generic Hensel's Lemma, masking the underlying algebraic structure. In this paper, we establish a structural isomorphism between the lifting process and the roots of a special auxiliary polynomial $V(x)$, unveiling a deterministic link to Dickson polynomials. Based on this theory, we develop \texttt{Dickson-Engine}, a linear-time algorithm ($O(ep)$) that outperforms standard libraries by orders of magnitude. Applying this engine to ${\mathbb{Z}}_{169}$, we explicitly construct a family of classical LCD codes of length $n=182$ via the isometric Gray map. Our search reveals codes with parameters (e.g., $[182,1,168{]}_{13}$ and $[182,2,144{]}_{13}$) that are \textbf{near-optimal} with respect to the theoretical Griesmer Bound. Notably, we discover a ``robustness plateau'' starting from non-trivial dimensions ($k=4$), where the minimum distance remains stable ($d=120$) even as the dimension triples ($k=4\to 12$). These codes provide exceptional resources for post-quantum cryptography and quantum error correction without entanglement consumption ($c=0$).

Full and extended version of the ISIT 2026 accepted paper. Updates in this version: Algorithm 1 has been refined to reflect the optimized 'single-seed lifting' implementation; the discussion on the 'robustness plateau' of LCD codes has been updated to clarify it as an intrinsic property of cyclic codes over local rings