We propose CHRONOS, a hardware-assisted framework that decouples the cryptographic setup required for private gradient aggregation from the active training phase. CHRONOS executes a once-per-epoch server-relayed Diffie-Hellman key exchange during a device's idle window. It generates ephemeral keypairs and derives PRG keys entirely within an ARM TrustZone enclave, ensuring private keys never exist in Normal World memory. Pairwise secrets are sealed in the enclave, and Shamir secret shares of the ephemeral private key are distributed to peers. During training, clients mask gradients with a single stream-cipher evaluation and transmit them in one communication round. A hardware-backed round counter enforces single-use freshness. If clients drop out mid-round, the server reconstructs their masks from peer-held Shamir shares, preserving correct aggregation without repeating the round. Evaluation on Rock Pi 4 devices using OP-TEE demonstrates that CHRONOS achieves OS-level compromise resistance and thwarts state-of-the-art gradient inversion attacks. It reduces active-phase aggregation latency by up to 74% compared to synchronous secure aggregation for 20 clients. The system maintains a persistent Secure World storage footprint of fewer than 700 bytes per device, scaling independently of model dimension.

翻译：我们提出CHRONOS——一种硬件辅助框架，将私有梯度聚合所需的密码学设置与主动训练阶段解耦。CHRONOS在设备空闲窗口期间执行每轮一次的服务端中继Diffie-Hellman密钥交换，并在ARM TrustZone可信执行环境内生成临时密钥对及派生PRG密钥，确保私钥永不出现于Normal World内存。成对秘密被密封于该环境内，同时将临时私钥的Shamir秘密共享份额分发给对等节点。训练阶段，客户端通过单次流密码计算掩盖梯度并在单轮通信中传输，硬件支持的轮次计数器强制执行单次新鲜性保障。若客户端在该轮中途掉线，服务器可从对等节点持有的Shamir份额中重构其掩码，无需重跑整轮即可保持正确聚合。基于Rock Pi 4设备与OP-TEE的评估表明：CHRONOS具备操作系统级抗攻陷能力，可抵御当前最先进的梯度逆向攻击；相较20个客户端的同步安全聚合方案，其主动阶段聚合延迟降低达74%。系统为每台设备维持小于700字节的持久化Secure World存储开销，且该规模与模型维度无关。