Okp

OKP is an acronym commonly used in cryptography to refer to Octet Key Pair, a public-key key type defined for use with JSON Web Algorithms (JWA) and JSON Web Key (JWK). The OKP format represents cryptographic keys as octet (byte) sequences rather than the traditional parameterized curves of older elliptic-curve systems.

In a JWK, an OKP key is identified by the key type kty set to OKP. The curve used is indicated by the crv parameter, which can be one of Ed25519, Ed448, X25519, or X448. The public key is carried in the x parameter, encoded as base64url. The private key, when present, is carried in the d parameter and is also base64url-encoded. This encoding makes OKP keys compact and easy to transport in web-based protocols.

OKP keys are designed for two main purposes. Ed25519 and Ed448 keys are intended for digital signatures, offering high security with small key sizes and fast computation. X25519 and X448 keys are intended for public-key agreement (diffie-hellman) and are valued for their strong security properties and performance, especially in constrained environments.

The OKP scheme is contrasted with traditional elliptic-curve (EC) keys by relying on fixed-size octet representations for keys, which simplifies interoperability in JSON-based security protocols. It is part of broader standardization efforts within the JOSE family, with formal definitions appearing in relevant RFCs that cover JWK and JWA.

See also: JSON Web Key, JSON Web Algorithms, Ed25519, X25519. Note that OKP can have other, less common meanings in different contexts, but in cryptography it refers to Octet Key Pair.