Re: Which authenttication is better
From: Renaissance Man (me@my.net)
Date: 12/14/02
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From: "Renaissance Man" <me@my.net> Date: Fri, 13 Dec 2002 19:34:18 -0500
Where is good source of information for understanding the security
implications of the various openssh options. I am still personally confused
over SSH1 or SSH2, and how strong or safe each method will be.
"Per Hedeland" <per@hedeland.org> wrote in message
news:arnq6p$175o$1@hedeland.org...
> In article <3DDF2DC3.9060404@doe.carleton.ca> Shing-Fat Fred Ma
> <fma@doe.carleton.ca> writes:
> >
> >#1:
> >Using protocol 2, am I to understand from the
> >man page that public key authentication is the
> >preferred way?
>
> I don't know why you think that, and I don't know the answer, since it
> depends on what exactly you mean by "preferred": The client has a
> predefined order that it will try authentication mechanisms in, and
> order that can be changed (as well as the list shortened) with
> PreferredAuthentications in the config file or on the command line.
>
> In some sense the first mechanism listed there is the "preferred" one,
> from the 3.4p1 man page it seems it is "hostbased". Which mechanism is
> "preferred" in a "general" sense isn't possible to answer, since it
> depends on many factors, e.g. required security, convenience, and last
> but not least personal opinion, of course... If one mechanism was simply
> "best" there would be no need for any others.:-)
>
> >#2:
> >They also say that "the
> >hostbased method" of protocol 1 is tried first,
> >but there are two "host" based methods. I
> >assume the obvious, that the one using
> >*known_hosts is used because the other one
> >is not secure (the one relying only on *hosts.equiv
> >or .[rs]hosts). Is this right?
>
> The question doesn't really make sense - the server config file
> determines whether the non-key-based one is allowed at all (by default
> it isn't). If it *is* allowed, it isn't any "more secure" to try the
> key-based one first - since if it fails, the non-key-based one will be
> tried anyway. But I think the ssh(1) man page makes it pretty clear that
> the non-key-based one is tried first with protocol 1.
>
> >#3:
> >Why would "the hostbased methods" be tried
> >before public key authentication? It seems like
> >the latter is more secure.
>
> See previous question - the order in which allowed mechanisms are tried
> doesn't have any real bearing on security. Thus it is determined by
> convenience/functionality - it doesn't make much sense to ask the user
> for a password / pass phrase (perhaps multiple times) and then let him
> in without using one.
>
> >#4:
> >I was presented with the server host's RSA
> >fingerprint to say "yes" or "no" to. To check
> >this fingerprint, I tried
> >
> > $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key.pub
> > ssh_host_rsa_key.pub is not a public key file.
> > $ ssh -l -f /etc/ssh/ssh_host_key.pub
> > SPAT_OUT_A_KEY_FINGERPRINT
> >
> >Which file is right one? I presumed the 1st one.
> >The fingerprint from the 2nd one didn't match
> >what I was presented.
>
> It depends on what protocol was being used, and of course on the server
> config file, which can name these files whatever it wants. But the
> default in OpenSSH is:
>
> # HostKey for protocol version 1
> #HostKey /etc/ssh/ssh_host_key
> # HostKeys for protocol version 2
> #HostKey /etc/ssh/ssh_host_rsa_key
> #HostKey /etc/ssh/ssh_host_dsa_key
>
> (i.e. version 2 can use either RSA or DSA; version 1 is always RSA).
>
> >#5:
> >Because of the error from the 1st keygen command,
> >I assumed it was commercial ssh format and tried:
> >
> > $ ssh-keygen -i -f /etc/ssh/ssh_host_rsa_key.pub
> >
> >It turns out that the file is not readable by
> >common users. Should it be, for the
> >purposes of extracting the fingerprint, which
> >in turn is for the purpose of confirming the
> >server host?
>
> Yes, it should be readable - or at least the server admin should
> "somehow" provide users that want it with the fingerprint or even the
> whole key (for installation on their clients). For the user to log in to
> the server and extract the fingerprint there isn't obviously useful,
> since that login session may already be compromised by a man-in-the-
> middle attack - i.e. it requires that the user has an alternate "secure
> path" (basically console connection) to the server.
>
> --Per Hedeland
> per@hedeland.org
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