X25519
also: Curve25519, curve25519-sha256
X25519 is an elliptic curve Diffie-Hellman key exchange algorithm that uses the Curve25519 elliptic curve. It enables two parties to establish a shared secret over an insecure channel for encrypting communications.
X25519 is a modern cryptographic key exchange protocol based on the Curve25519 elliptic curve, designed by Daniel J. Bernstein. It allows two parties to derive a shared secret from their respective public keys without ever transmitting the secret itself, making it suitable for establishing encrypted connections.
The algorithm is highly favored in Linux systems because it is faster and more secure than older key exchange methods like Diffie-Hellman (DH) and ECDH. X25519 is specifically optimized for performance on general-purpose processors and resists timing attacks due to its constant-time implementation.
Common uses include SSH key exchange, TLS/HTTPS encryption, and VPN protocols like WireGuard. For example, modern SSH implementations support X25519 for key negotiation: ssh -o KexAlgorithms=curve25519-sha256 user@host
X25519 produces a 256-bit shared secret and is considered quantum-resistant relative to older elliptic curves, making it a cryptographic standard in contemporary Linux security infrastructure.