#528 ssh keys: ECDSA and ed25519 key type support

[Mikhail Yakshin]

As mentioned at SSH key info page, SF currently supports only RSA and DSA keys. However, OpenSSH upstream deprecated DSA key support since 7.0. Support for alternative key types, such as ECDSA and ed25519, has been available since OpenSSH 5.7 and 6.5 respectively, that is 2011 and 2014 - 5 years ago and 2 years ago.

All alternative key types have their benefits: lower CPU usage, smaller key length, faster handshakes, etc.

I suggest to have these new keys types to be supported at SF for auth purposes.

[Dave Brondsema]

[#479]