Cryptography Glossary

Scope and how to use this glossary

This article covers cryptographic objects, algorithms, services, protocols, infrastructure terms, implementation terms, and common acronyms that recur in the Knowledge Base. It is intentionally concise: an entry states what a term means and, where useful, what it does not mean. The cited sources include final NIST publications and an IETF proposed standard. Their terminology is authoritative within their stated documents, but it should not be treated as context-free across every standard. NIST SP 800-57 Part 1 Rev. 5 says that its glossary definitions are defined as used in that document and that the same terms may be defined differently elsewhere.1

Read the entries in conceptual order: security services describe the protection sought; algorithms and keys provide mechanisms and parameters; key management governs key life cycles; certificates and PKI bind public-key information to identities; TLS applies authenticated key exchange and session protection at the protocol level. For broader background, see the Knowledge Base articles on cryptography, symmetric versus asymmetric cryptography, PKI, and cryptographic algorithms.12

Security services

Authentication is a security service addressed by cryptographic mechanisms. In practice, distinguish identity authentication from source authentication: the former concerns the identity of an entity, while the latter concerns the source of information. The cited NIST material lists confidentiality, data integrity, authentication, authorization, and nonrepudiation among services provided or supported by cryptography.12

Confidentiality is protection against unauthorized disclosure. Encryption is commonly used to provide it, but confidentiality depends on more than selecting an algorithm: the associated keying material and its protection are also central. NIST states that the security of information protected by cryptography directly depends on protection afforded to key information.2

Data integrity is assurance that data has not been changed in an unauthorized or undetected way. A secure hash digest can help detect whether a message changed after the digest was generated, while an authenticated construction can additionally provide assurance about an authorized source. Integrity and confidentiality are therefore different properties.3

Authorization concerns whether an entity is permitted to perform an action or access a resource. It should not be used as a synonym for authentication: authentication addresses identity or source, whereas authorization addresses permission. Nonrepudiation is listed by NIST as a security service supported by cryptographic mechanisms; its interpretation depends on the governing system, policy, and evidence requirements.1

Keys, keying material, and key management

Cryptographic key: a parameter used with a cryptographic algorithm that determines the algorithm’s operation so that an entity with knowledge of the key can use the algorithm as intended by the scheme. A key is not the same thing as a password, certificate, algorithm, or encrypted data object, even though those objects can be related operationally.1

Keying material: information associated with cryptographic keys and their use. The cited NIST guidance emphasizes that keys and associated secret metadata need protection against unauthorized disclosure. Key management is the discipline covering the secure generation, storage, distribution or establishment, use, and destruction of keys across the key’s life.2

Cryptographic key management system (CKMS): a system required to manage keys and information associated with them. The term describes management functionality and controls, not a particular product. A CKMS must be considered alongside algorithm selection, key size, policy, access control, backup, recovery, replacement, and destruction; the cited evidence identifies these as related key-management topics but does not prescribe one universal architecture.2

Cryptoperiod: the period during which a key is authorized for a specified use. NIST notes that a cryptoperiod may be shortened to limit how long a key-management system maintains status information, while longer periods can be justified in circumstances where replacing many distributed keys is especially costly. For an asymmetric key pair, the two keys can have separate periods: an originator-usage period for applying protection, such as creating a signature, and a recipient-usage period for processing protected information, such as verifying that signature.1

Algorithms and cryptographic primitives

Cryptographic algorithm: a specified computational procedure used to provide a cryptographic function, such as encryption, digital signatures, hashing, key establishment, or random bit generation. Algorithm choice is not interchangeable with key management: NIST treats algorithms, infrastructures, protocols, implementations, applications, and management as related but distinct parts of cryptographic protection.1

Symmetric-key algorithm: an algorithm category using related secret keying material for the communicating or processing parties. Asymmetric-key algorithm: an algorithm category using a key pair, with separate key roles such as applying and processing cryptographic protection. These category labels describe key relationships; they do not, alone, specify a protocol, security service, or acceptable deployment.1

Block cipher: a family of permutations of fixed-size data blocks parameterized by a bit sequence called the key. The Advanced Encryption Standard (AES) is specified in FIPS 197 Update 1 as AES-128, AES-192, and AES-256. Each transforms 128-bit data blocks, and the suffix indicates the associated key length. AES is therefore a standardized block-cipher family, not a synonym for all encryption or all symmetric cryptography.5

Hash function and message digest: FIPS 180-4 specifies Secure Hash Algorithms (SHA) for generating digests of messages. The digest is a condensed representation used to detect whether a message has changed since the digest was generated. A digest is not a reversible encryption of the message, and the cited passage does not say that an unkeyed digest authenticates its source.3

Digital signature: a cryptographic operation in which one asymmetric key is used to apply protection, such as creating a signature, and the corresponding key is used to process that protected information, such as verifying the signature. A signature should not be described simply as encryption: its role and security properties are different.1

Random bit generation: the generation of random bits for cryptographic use. NIST SP 800-175B identifies random bit generation as part of cryptographic guidance and places it alongside key-establishment mechanisms and key-management systems. The cited evidence does not provide a complete definition of randomness, entropy estimation, or a specific generator design.2

PKI, certificates, and revocation

Public key infrastructure (PKI): the infrastructure and associated components used to support public-key applications. The cited NIST material identifies SP 800-32 as an introduction to PKI, while IETF RFC 5280 defines a profile for Internet X.509 PKI certificates and certificate revocation lists. This glossary therefore uses PKI as an infrastructure concept rather than equating it with a single certificate, algorithm, or product.

Certificate: an object in the X.509 PKI ecosystem used with public-key infrastructure. RFC 5280 defines certificate and certificate-revocation-list profiles and specifies representations, extensions, and identifiers used by conforming PKI components. A certificate is not itself a secret key; it is associated with public-key and identity-related information in the PKI profile.

Certification authority (CA): an authority in the PKI context that issues certificates and can publish certificate status information. RFC 5280 states that a CRL issuer is either the CA or an entity authorized by the CA to issue CRLs; a CA may delegate that responsibility.

Certificate revocation list (CRL): a published object providing status information about certificates issued by a CA. RFC 5280 describes a CRL as having a defined scope—the set of certificates that could appear on that CRL—and permits other revocation or certificate-status mechanisms in environments where CRLs are not issued. A CRL is therefore not identical to the certificate it describes.

Online Certificate Status Protocol (OCSP): a certificate-status mechanism referenced by TLS 1.3, which updates how OCSP messages are carried. The cited evidence does not provide a full OCSP definition, so this entry should be read as a contextual distinction from CRLs rather than a protocol specification.

Protocols, modules, validation, and approval status

Transport Layer Security (TLS): a protocol in which the handshake is an authenticated key exchange intended to support one-way authenticated or mutually authenticated functionality. At handshake completion, each side obtains session keys, cryptographic parameters, and the identities of the communicating parties. TLS is therefore a protocol that coordinates cryptographic mechanisms; it is not itself a hash function, key, or certificate.

Handshake: in TLS terminology, the initial negotiation between client and server that establishes parameters for subsequent interactions. A client initiates the TLS connection; a server is the other endpoint in the cited TLS terminology. An endpoint is either client or server, while a peer refers to the endpoint that is not the primary subject of discussion.

Cryptographic module: a module containing cryptographic algorithms and used in products or systems to provide services such as confidentiality, integrity, and authentication. FIPS 140-3 covers secure design, implementation, and operation of cryptographic modules, including interfaces, roles, services, authentication, software or firmware security, physical security, sensitive security parameter management, self-tests, lifecycle assurance, and attack mitigation.

Validation: an assurance activity associated with testing implementations against established standards. NIST identifies the Cryptographic Algorithm Validation Program (CAVP) and Cryptographic Module Validation Program (CMVP) as programs for validating approved algorithm implementations and cryptographic modules. Validation is not the same as claiming that every deployment is secure: the cited evidence also warns that poor design or weak algorithms can render a product insecure.

Acceptable, deprecated, legacy use, and disallowed: approval-status terms used in NIST SP 800-131A Rev. 2. The status of an algorithm can depend on key length, domain parameters, and the mode or manner of use. These labels must not be treated as properties of an algorithm name in isolation.

Federal Information Processing Standard (FIPS) and Special Publication (SP): FIPS is expanded in FIPS 180-4 as Federal Information Processing Standard; NIST publications use SP for Special Publication. The cited sources include FIPS 197 Update 1, FIPS 180-4, FIPS 140-3, and NIST SP 800-series recommendations. Document status and version matter: for example, FIPS 197 was published November 26, 2001 and updated May 9, 2023, while RFC 5280 is identified as a proposed standard and RFC 8446 as an IETF standards-track document in the cited bundle.

Conclusion

A useful cryptography vocabulary keeps services, algorithms, keys, protocols, and governance distinct. Start by naming the property required—confidentiality, integrity, authentication, authorization, or another service—then identify the algorithm and key relationship, account for key management and security strength, and finally place the mechanism in its PKI, TLS, module, validation, and approval-status context. Always check the governing document and version because terminology and approval status can be document-specific. claim-02claim-0912