Creating user specific authentication methods in SSH

Question

1. I have configured sshd on an Ubuntu server to use key authentication and it is working fine.
2. I had to disable password authentication for key authentication to work.
3. Server is always accessed via remote terminals or putty.

Now all user accounts are able to login with the authentication key and passphrase. But now I want to create only one new user without key authentication. So how should I go about doing this in such a way that does not hamper other users who are using key authentication.

Answer 1

You can use Match in sshd_config to select individual users to alter the PasswordAuthentication directive for. Enter these Match rules at the bottom of sshd_config file ( generally /etc/ssh/sshd_config )

Match User root,foo,bar
    PasswordAuthentication no
Match User Rishee
    PasswordAuthentication yes

This would give root, foo and bar key authentication, and Rishee password authentication.

An alternative is to match by negation, like this:

PasswordAuthentication no
Match User *,!root
    PasswordAuthentication yes

In this case, everyone except root gets password authentication.

Note: The *, syntax is necessary, as wildcard and negation syntax is only parsed in comma-separated lists.

You can also match by group:

Match Group usergroup
    PasswordAuthentication no

Reason for entering Match at the bottom of the file:

If all of the criteria on the Match line are satisfied, the keywords on the following lines override those set in the global section of the config file, until either another >Match line or the end of the file

Answer 2

You can enable password and key-authentication at the same time, they are not exclusive.