SSH publickey autentication - server accepts key but auth does not succeed

Question

I'm helping a friend who has some trouble connecting using public-key authentication, to a server maintainied by me. Public-key auth works fine for a couple of other users. Of course, my friend's public key is in authorized_keys-file on the server.

debug1: Host 'xxxxx' is known and matches the RSA host key.
debug1: Found key in /home/xxx/.ssh/known_hosts:3
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found
debug1: Unspecified GSS failure.  Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found
debug1: Unspecified GSS failure.  Minor code may provide more information
debug1: Unspecified GSS failure.  Minor code may provide more information
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/xxx/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Offering RSA public key: [email protected]
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Trying private key: /home/xxx/.ssh/id_dsa
debug1: Trying private key: /home/xxx/.ssh/id_ecdsa
debug1: Next authentication method: password

The following line does not make sense to me

Server accepts key: pkalg ssh-rsa blen 279

Since it seems that the server thinks that the public-key is perfectly correct, so why does it continue to password-authentication instead of authenticating the user?

Answer 1

I believe that you are showing client-side logs/debugging output. I would look at the server-side logs as that usually gives more detail about why the server rejected a public-key authentication attempt.

E.g. insecure permissions on users home or .ssh directories.

Answer 2

In my case, the issue was that the user it was attempting to connect as was root, and I had disabled root ssh login (which probably everyone should do). So, make sure your friend is attempting to connect via the correct, non-root user account.

Answer 3

I have recently experienced this with Gerrit's SSH interface. The problem was that my local SSH agent offered up a bunch of different keys to the Gerrit server, and after some limit the server just refused to accept further keys (but still replied with the Server accepts key). I don't know if this behavior is specific to Gerrit or a generic OpenSSH thing.

The fix was to force select the right key in ~/.ssh/config:

Host gerrit.example.org
  IdentityFile ~/path/to/my_key
  IdentitiesOnly yes

After making sure that ~/path/to/my_key.pub exists (it can be created with ssh-keygen -f ~/path/to/my_key -y > ~/path/to/my_key.pub), the ssh agent could provide the key without having to re-enter the passphrase, but did not provide any other keys.