My current version of OpenSSH :

• OpenSSH_6.0p1-hpn13v11, OpenSSL 1.0.1c 10 May 2012

And generating a key with

{{{
ssh-keygen -t ecdsa -b 521
}}}

Generates a public key with the following leading:

{{{
ecdsa-sha2-nistp521
}}}

However, the sites public key submission field rejects my public key regardless of what I do