OS X 10.13.2 High Sierra SSH Invalid key length

Apple OS X 10.13.2 High Sierra latest update has defaulted to 2048 key length and SHA256 algorithm. This breaks all existing SSH keys that are lower e.g. 1024 or in PEM format. The error thrown by the SSH client is “Invalid key length”.

None. Generate a new key pair with ssh-keygen and update remote servers with the public key.