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Security Fundamentals & Crypto · Intermediate

Ephemeral Key

A key generated for a single session or transaction and discarded afterward.

Definition

Ephemeral keys, such as those in DHE and ECDHE, ensure that compromise of a long-term key cannot decrypt past sessions. They are the mechanism behind perfect forward secrecy. Static keys, by contrast, are reused across many sessions.

Example

An ECDHE key pair is generated per TLS handshake and wiped from memory afterward.

Exam tip

Ephemeral (the E in DHE/ECDHE) means forward secrecy.

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