Encryption
Transforming plaintext into ciphertext using a key so only authorized parties can read it.
Encryption protects confidentiality both at rest (full-disk, database, file) and in transit (TLS, IPsec, VPN). Symmetric ciphers like AES are fast and used for bulk data; asymmetric ciphers like RSA and ECC are slower but solve key exchange and enable digital signatures — so real systems typically use asymmetric crypto to exchange a symmetric session key, then encrypt the data itself symmetrically.
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