Kriptograafias

Cryptography is the study and practice of secure communication in the presence of adversaries. It encompasses techniques for concealing information, ensuring its integrity, and authenticating users and devices. The core goals are confidentiality, data integrity, authenticity, and non-repudiation.

Cryptographic systems rely on mathematical properties that make certain operations easy to perform in one direction but hard to reverse without a secret key. They are implemented as algorithms and protocols that define how data is transformed, stored, and exchanged.

There are two broad families: symmetric encryption, which uses a single key for encryption and decryption, and asymmetric (public-key) encryption, which uses a key pair. Examples include AES and ChaCha20 for symmetric; RSA and ECC (including Ed25519) for asymmetric. Key exchange protocols like Diffie-Hellman enable two parties to establish a shared secret over an insecure channel.

Cryptographic hashes produce fixed-length digests and are used for data integrity, while also supporting digital signatures and authentication. Hash properties include preimage resistance, second-preimage resistance, and collision resistance. Digital signatures, created with private keys, verify origin and integrity; common schemes include RSA, ECDSA, and Ed25519.

Security relies on computational hardness assumptions and, where possible, formal proofs. Standards bodies (such as NIST and ISO) evaluate and publish recommended algorithms. Cryptography enables secure web traffic (TLS), secure messaging, encrypted storage, and secure financial transactions; it also underpins blockchain technologies through hashes and digital signatures.