# What is Cryptography?

> Cryptography is the discipline of designing, analyzing, and applying mathematical techniques to protect information and communications against defined adversaries.

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## Content

It supplies primitives and constructions for properties such as confidentiality, integrity, origin authentication, entity authentication, and evidence that may support non-repudiation, then combines them within protocols and systems whose security depends on explicit assumptions, keys, parameters, and operating conditions.

Its tools include encryption, cryptographic hash functions, message authentication codes, digital signatures, key-establishment methods, and secure random-bit generation. Selecting an approved primitive is only one part of engineering a secure implementation and lifecycle.

### Key points

- **Purpose and model:** State the required security property, protected assets, adversary capabilities, trust boundaries, acceptable algorithms and parameters, and the protocol context in which a primitive will be used.
- **Keys and randomness:** Generate unpredictable values, protect private or secret keys, bind keys to authorized purposes, distribute them securely, rotate or replace them when required, and destroy them appropriately.
- **Implementation and maintenance:** Use reviewed constructions and libraries, avoid unsafe composition, test interoperability and failure handling, reduce side-channel exposure, and migrate before algorithms or parameter sizes become unsuitable.
- **Important limitation:** Cryptography does not make an entire system secure. Correct primitives can be defeated by weak randomness, key theft, protocol mistakes, vulnerable endpoints, metadata leakage, implementation defects, obsolete parameters, or misuse by an authorized party.

### Related terms

[Encryption](<https://yellowcube.eu/glossary/encryption/>) · [Message authentication code (MAC)](<https://yellowcube.eu/glossary/message-authentication-code/>) · [Public key infrastructure (PKI)](<https://yellowcube.eu/glossary/public-key-infrastructure/>) · [Post-quantum cryptography (PQC)](<https://yellowcube.eu/glossary/post-quantum-cryptography/>) · [Homomorphic encryption](<https://yellowcube.eu/glossary/homomorphic-encryption/>) · [Cryptographic hashing](<https://yellowcube.eu/glossary/cryptographic-hashing/>) · [Transport Layer Security (TLS)](<https://yellowcube.eu/glossary/transport-layer-security/>)

### Sources

[NIST Cryptographic Standards and Guidelines](https://csrc.nist.gov/Projects/cryptographic-standards-and-guidelines) · [NIST SP 800-175B Rev. 1: Guideline for Using Cryptographic Standards](https://csrc.nist.gov/pubs/sp/800/175/b/r1/final) · [NIST SP 800-57 Part 1 Rev. 5: Recommendation for Key Management](https://csrc.nist.gov/pubs/sp/800/57/pt1/r5/final)

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