[Bug 2309] New: change default PreferredAuthentications order

bugzilla-daemon at mindrot.org bugzilla-daemon at mindrot.org
Sat Nov 8 10:38:42 EST 2014


            Bug ID: 2309
           Summary: change default PreferredAuthentications order
           Product: Portable OpenSSH
           Version: 6.7p1
          Hardware: Other
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: calestyo at scientia.net


As far as I understand, one cannot "improve" the security of SSH by
disabling auth methods or changing their order... on the client

- Even if one thinks e.g. password or hostbased are insecure, as long
as they're enabled on the server side, one cannot "protect" such server
by disabling it on the client side.

- Neither can one improve the security of the one's own current
session, since that is already fully set up after the KEX (both plain
KEX or GSS KEX) and thus *before* auth takes places.

Right so far?

If so, then the only sense of the default order of auth methods is
probably usability, i.e. the less interaction necessary by the user,
the better.

The current default is:

Which is IMHO already close to perfect:

keyboard-interactive,password come last, since they always require
manual user input.

publickey - may or may not require manual input (depending on whether
the identity key is encrypted or not), thus it should be before the two
with passphrase entry

But then I'd swap gssapi-with-mic with hostbased:
gssapi-with-mic: a krb ticket may not be available, if not the user
would need create one first likely requires passphrase input as
well,... but they ticket may also be already there (thus no further
interaction needed) which is why it should come before pubkey

hostkey: well AFAIU, it either works (if enabled and ssh-keysign is
activated) or not. No interaction for the user.


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