"The good news: the only affected key type is 521-bit ECDSA. That is, a key that appears in Windows PuTTYgen with ecdsa-sha2-nistp521 at the start of the 'Key fingerprint' box, or is described as 'NIST p521' when loaded into Windows Pageant, or has an id starting ecdsa-sha2-nistp521 in the SSH protocol or the key file. Other sizes of ECDSA, and other key algorithms, are unaffected. In particular, Ed25519 is not affected. "
dirksteins