[cryptography] ssh-keys only and EKE for web too (Re: preventing protocol failings)

Adam Back adam at cypherspace.org
Wed Jul 13 06:49:53 EDT 2011


You know this is why you should use ssh-keys and disable password
authentication.  First thing I do when someone gives me an ssh account.

ssh-keys is the EKE(*) equivalent for ssh.  EKE for web login is decades
overdue and if implemented and deployed properly in the browser and server
could pretty much wipe out phishing attacks on passwords.

We have source code for apache, mozilla, maybe could persuade google; and
perhaps microsoft and apple could be shamed into following if that was done.

Of course one would have to disable somethings (basic auth?) and do some
education - never enter passwords outside of the browsers verifiably local
authentication dialog - but how else are we going to get progress, this is
2011, and the solution has been known for nearly 20 years - its about time
eh?  Maybe you could even tell the browser your passwords so it could detect
and prevent users typing that into other contexts.

(*) The aspect of EKE like SRP2 that fixes the phising problems is you dont
send your password to the server, the authentication token is not offline
grindable (even to the server), and the authentication token is bound to the
domain name - so login to the wrong server does not result in the phishing
server learning your password.

Adam

>I can second that with an observation made by several users of the
>German Research Network (DFN), in December 2009. Someone had registered
>a long list of typo domains, i.e. domains like tu-munchen.de instead of
>tu-muenchen.de, and then installed an SSH daemon that would respond on
>all subdomains.
>
>Some users (including a colleague and myself) noticed that they suddenly
>got a host-key-mismatch warning when accessing their machines via SSH -
>and found that they had mistyped the host name *and still got an SSH
>connection*. Neither my colleague nor me had entered our passwords yet,
>but that was only because we were sensitive to host key changes at that
>moment because we had re-installed the machines just a few days before
>the event.
>
>The server that delivered the typo domains was located in South Africa,
>BTW. I don't even know if legal persecution is possible, and I don't
>think anyone attempted. The DFN reacted in a robust way by blocking
>access to the typo domains in their DNS. Not a really good way, but
>probably effective for most users.
>
>The question, after all, is how often do you really read the SSH
>warnings? How often do you just type on or retry or press "accept"? What
>if you're the admin who encounters this maybe 2-3 times day?
>
>(Also, Ubuntu, I believe, has been known to change host keys without
>warning when doing a major update of openssh.)
>
>Ralph
>
>-- 
>Dipl.-Inform. Ralph Holz
>I8: Network Architectures and Services
>Technische Universität München
>http://www.net.in.tum.de/de/mitarbeiter/holz/
>



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