Cryptography
The practice and study of techniques for securing communication in the presence of adversaries.
Cryptography delivers confidentiality (encryption), integrity (hashing), authentication, and non-repudiation (digital signatures) — the building blocks under nearly every other control. Per Kerckhoffs’s principle, security must rest on key secrecy, not algorithm secrecy. Quantum-resistant (post-quantum) algorithms are the next frontier; NIST has standardized initial PQC schemes to survive future quantum attacks against RSA and ECC.
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