Blue Flower

This was taken from

The Windows SSH client PuTTY does not support ECDSA as of March 2016. One needs a PuTTY development snapshot to connect to a server that uses only ECDSA keys.

Ed25519 was introduced in OpenSSH 6.5: "Ed25519 is an elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance". Its main strengths are its speed, its constant-time run time (and resistance against side-channel attacks), and its lack of nebulous hard-coded constants.[11] See also this blog post by a Mozilla developer on how it works.

It is already implemented in many applications and libraries and is the default key exchange algorithm (which is different from key signature) in OpenSSH.

Ed25519 key pairs can be generated with:

# ssh-keygen -t ed25519

There is no need to set the key size, as all Ed25519 keys are 256 bits. Also, they rely on a new key format which "uses a bcrypt-based key derivation function that makes brute-force attacks against stolen private keys far slower".

For those reasons, compatibility with older versions of OpenSSH or other SSH clients and servers may prove troublesome.