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A short-term key pair used with a public-key (asymmetric-key) algorithm that is generated when needed; the public key of an ephemeral key pair is not provided in a public key certificate, unlike static public keys which are often included in a certificate.
NIST SP 800-175B Rev. 1
A key pair, consisting of a public key (i.e., an ephemeral public key) and a private key (i.e., an ephemeral private key) that is intended for a very short period of use. The key pair is ordinarily used in exactly one transaction of a cryptographic scheme; an exception to this is when the ephemeral key pair is used in multiple transactions for a key-transport broadcast. Contrast with a static key pair.
NIST SP 800-56A Rev. 2 [Superseded]