The file ~/.ssh/authorized_keys lists the public keys that are permitted
     for logging in.  When the user logs in, the ssh program tells the server
     which key pair it would like to use for authentication.  The client
     proves that it has access to the private key and the server checks that
     the corresponding public key is authorized to accept the account.
...
(id_rsa)
identity_file
             Selects a file from which the identity (private key) for public
             key authentication is read.  The default is ~/.ssh/identity for
             protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and
             ~/.ssh/id_rsa for protocol version 2.  Identity files may also be
             specified on a per-host basis in the configuration file.  It is
             possible to have multiple -i options (and multiple identities
             specified in configuration files).  ssh will also try to load
             certificate information from the filename obtained by appending
             -cert.pub to identity filenames.
...
(id_rsa.pub)
The user creates his/her key pair by running ssh-keygen(1).  This stores
     the private key in ~/.ssh/identity (protocol 1), ~/.ssh/id_dsa (protocol
     2 DSA), ~/.ssh/id_ecdsa (protocol 2 ECDSA), or ~/.ssh/id_rsa (protocol 2
     RSA) and stores the public key in ~/.ssh/identity.pub (protocol 1),
     ~/.ssh/id_dsa.pub (protocol 2 DSA), ~/.ssh/id_ecdsa.pub (protocol 2
     ECDSA), or ~/.ssh/id_rsa.pub (protocol 2 RSA) in the user's home direc‐
     tory.  The user should then copy the public key to ~/.ssh/authorized_keys
     in his/her home directory on the remote machine.  The authorized_keys
     file corresponds to the conventional ~/.rhosts file, and has one key per
     line, though the lines can be very long.  After this, the user can log in
     without giving the password.
...
(known_hosts)
ssh automatically maintains and checks a database containing identifica‐
     tion for all hosts it has ever been used with.  Host keys are stored in
     ~/.ssh/known_hosts in the user's home directory.  Additionally, the file
     /etc/ssh/ssh_known_hosts is automatically checked for known hosts.  Any
     new hosts are automatically added to the user's file.  If a host's iden‐
     tification ever changes, ssh warns about this and disables password
     authentication to prevent server spoofing or man-in-the-middle attacks,
     which could otherwise be used to circumvent the encryption.  The
     StrictHostKeyChecking option can be used to control logins to machines
     whose host key is not known or has changed.