Secure data handling in mission computers means protecting data at rest and in transit, managing cryptographic keys securely, and guarding against side-channel leaks that could reveal sensitive information. Encrypting data at rest ensures that any stored information—on disks, flash, or backups—remains unreadable without the proper keys, so physical access to storage doesn’t expose the data. Encrypting data in transit protects information as it moves between devices or networks, using protocols like TLS or IPsec to keep content confidential and verify integrity and authenticity of communications. Key management ties everything together. Keys should be rotated regularly to limit exposure if a key is compromised, and keys should be stored in hardware-backed secure storage rather than in plain software memory. This reduces the risk of keys being extracted if the system is breached and supports safer key lifecycle practices like revocation and re-issue. Side-channel protection addresses risks that aren’t about the data in storage or in transit but about how cryptographic operations can leak information through timing, power, or electromagnetic signatures. Implementing constant-time algorithms and other mitigations helps prevent attackers from deducing keys or plaintext from such leaks. Together, these elements form a comprehensive approach: data protection at rest and in transit, robust key management with rotation and secure storage, and defenses against side-channel leakage. Partial measures—such as encrypting only stored data or only securing transit—leave gaps, while including all these aspects provides strong, defense-in-depth security for mission-critical systems.