Functional Converses for Private Matrix-Product Retrieval under Library-Wide Decoder-Side Correlation

arXiv:2611.07325v1 Announce Type: new Abstract: We consider private retrieval of the matrix product $A^\top B^{(\theta)}$ from replicated $P_c$-colluding servers when $B^{(\ell)}=A+N^{(\ell)}$, with the innovations mutually independent and independent of the user-held $A\in\mathbb{F}_q^{m\times m}$. The servers store the full library, correlated with $A$, which changes both the communication problem and the security definition: a secrecy condition including the stored library cannot hold, as the library itself partly reveals $A$. We therefore measure only additional leakage and require index privacy conditioned on $A$; both reduce to classical notions under independence. For $A$ of rank $k