1

As sshd service can listen on different ports is it possible to configure a key which will work only if the connection was made on one port, but not the other?

By this I mean that the key appears more than once in the authorized_keys list and the connection will be permitted if it is made on the port specified in the key.

The idea is to use the same key but with a different command= and other option to allow the same key to be used for different services.

3

Surely you can:

Port 2222
Port 3333
Match LocalPort 2222
        AuthorizedKeysFile /path/to/authorized_keys_1
Match LocalPort 3333
        AuthorizedKeysFile /path/to/authorized_keys_2

See the Match section of the sshd_config(5) manpage for more info about which criteria and directives you can use with a Match block.

  • Can the AuthorizedKeysFile contain more than key, like when multiple users are connecting to a service that port is dedicated to? Can it also be extended to a source ip address or range? – vfclists Jan 14 at 11:58
  • 1
    Yes and yes. You can use multiple conditions in the Match directive: eg. Match LocalPort 2222 Address 172.31.17.252/30 to only apply to clients which connect to the port 2222 from the 172.31.17.252-172.31.17.255 address range. Notice that you can experiment with sshd by running it as a regular user (as long as you don't bind to ports < 1024 and don't try to auth other users, you can do almost everything). – mosvy Jan 14 at 15:42
  • Whether this setup provides any additional security benefits is another question... – Mark Jan 14 at 20:19

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