ECDHEPHEMERAL

ECDHEPHEMERAL, short for ephemeral Elliptic-Curve Diffie-Hellman, is a key-exchange method used to establish a secure channel in modern cryptographic protocols. It relies on elliptic-curve cryptography to perform Diffie-Hellman exchanges with temporary, per-session key material, rather than long-term keys.

In an ECDHEPHEMERAL exchange, both parties generate temporary EC key pairs for the session and share their public keys. They then combine their private key with the other party’s public key using Elliptic-Curve Diffie-Hellman to compute a shared secret. From this shared secret, session keys for encryption and integrity are derived. A defining feature is that the ephemeral private keys are discarded after the session, so the security of past communications does not depend on the security of long-term keys.

The principal security benefit of ECDHEPHEMERAL is forward secrecy: even if a server’s private key is compromised in the future, previously established sessions cannot be decrypted because the session keys were derived from ephemeral key material. This reduces the risk posed by key compromise and limit-eavesdropping threats. Potential downsides include higher computational and bandwidth costs due to generating and exchanging ephemeral keys, though modern hardware mitigates performance concerns. Proper implementation requires secure generation of random numbers, careful curve selection, and protection against side-channel attacks.

Common curves used with ECDHEPHEMERAL include NIST P-256 (prime256v1) and the Edwards curve X25519, chosen for a balance of security and performance. ECDHEPHEMERAL is a core component of secure protocols such as TLS, where it enables forward secrecy and strong authentication during handshake. See also Elliptic-curve Diffie-Hellman, Forward secrecy, and TLS.