The ability to use public keys to connect to SSH servers are coming with the next version.
>> "Which key exchange algos are used in the ssh implementation?"
With the current version out, the key exchange alogrithms are: diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, diffie-hellman-group-exchange-sha1
With the upcoming version, at least the following methods will be supported: diffie-hellman-group1-sha1, diffie-hellman-group14-sha1, diffie-hellman-group-exchange-sha1, diffie-hellman-group-exchange-sha256