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Is it possible to force specific users to login with public key, while allowing other users to login with password? Since public key authentication (with passphrase) is stronger than password-only authentication, we would like to require sudoers to login with public key. However, it is less convenient to force normal users to do so. In sshd_config, I don't see any policy-related configuration. Thanks for help.

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migrated from stackoverflow.com Feb 22 '11 at 15:53

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up vote 5 down vote accepted

You have a few options. In this answer I'm going to assume you have a sudoers group defined.

Take a look at the sshd_config man page, and look for the Match directive. This lets you specify configuration blocks that apply only to a subset of your ssh connections. You could do something like this:

Match Group sudoers
PasswordAuthentication no
ChallengeResponseAuthentication no

You could in theory accomplish something similar with a PAM configuration that would simply fail authentication attempts by people in the sudoers group. This would probably involve the pam_succeed_if module...you could add something like this to your auth config for sshd:

auth        requisite     pam_succeed_if.so user notingroup sudoers quiet

This means that only people not in the sudoers group can authentication via PAM. Note that this is untested. You could also use the pam_listfile module to do something similar.

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Thanks! I must also note that the Match directive is introduced in OpenSSH 5.0. For conservative distributions like CentOS, it may not be available natively. –  Crend King Feb 23 '11 at 8:44
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