I found the instructions in this link. In profile of putty, in the username field i must not add @hostname (ex user@srv1).

Notes

We create the keys with puttygen and we add the public key in the fileĀ  ~/.ssh/authorized_keys.

if you cannot connect and you receive this mesasge:

Authentication refused: bad ownership or modes for directory /home/user

change the permissions of the file authorized_keys:

chmod go-w ~/
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Convert key for SSH android app

(… this section is under construction …)

Links