ShieldLink: Retry‑Aware Authenticated Encryption for Secure and Reliable Chiplet Interconnects

Chiplet-based systems-in-package increasingly rely on die-to-die (D2D) links such as UCIe/CXL, where link-layer ARQ typically ensures reliability. At the same time, confidentiality and integrity are protected by higher-layer authenticated encryption (AEAD). When these layers are composed naively, the ARQ receiver can acknowledge and commit a frame based on a fast CRC/sequence check before the slower AEAD verification completes, creating a time-of-check to time-of-use (TOCTOU) window that can desynchronize state or enable denial-of-service. We introduce ShieldLink, a retry-aware link-security protocol that enforces a simple deliverability invariant: receive-side window advancement is gated on successful AEAD verification of exactly the bits that will be delivered. ShieldLink defines a fixed-payload ShieldLink frame (SLF) and two operating modes: Mode A authenticates each SLF, whereas Mode B amortizes authentication over an epoch of M frames to reduce per-frame overhead. Using Ascon-AEAD128 (based on ASCON-128a) as the representative AEAD and a Gilbert–Elliott burst-error model, we quantify wire efficiency, goodput, and tail commit latency relative to a secure “naïve stacking” baseline. Mode A eliminates the validity-before-verification race while improving goodput by approximately 2.4–2.5 percentage points at π_B ∈ {0.01, 0.05} and preserves low p99 commit latency. Mode B improves wire efficiency (e.g., 0.926 at M=32) and outperforms Mode A at low burst rates, but exhibits an epoch-retransmission cliff and crosses below Mode A near π_B≈0.035 in our default burst regime. These results provide concrete design guidance for integrating lightweight AEAD into future chiplet interconnects without sacrificing link-layer deliverability.