[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Inf-IT DAVcl] Blank page,with Internet Explorer


Sorry about the delay, but here's my follow-up, as promised. I'll break your reply down to the core questions/concerns, for brevity's sake.

I think in light of basic auth, digest auth looks more like fort knox
-bcrypt would be fort nox; MD5 (digest uses it exclusively https://httpd.apache.org/docs/2.4/misc/password_encryptions.html#digest) is the cryptographic equivalent of a bridge made of straws (way too fast and not salted) -"The original author of the MD5 password hash algorithm has publicly declared his software end-of-life and is "no longer considered safe" to use on commercial websites." June 2012 http://www.zdnet.com/article/md5-password-scrambler-no-longer-safe/ (sources should be linked throughout the article)

TLS only addresses "end-to-end" encryption, but does not protect you from host-related threats. -If this is truly your primary concern, you should be writing your own authentication mechanism to address the security gap (or forgo passwords http://www.cnet.com/news/google-security-exec-passwords-are-dead/). Digest's approach to only transfer and store hashes seems ideal, but it utilizes a weak hashing algorithm. Basic supports the strongest hashing algorithms, but decrypts the TLS packets before hashing and verifying the password. Basic is considered the "go to" because out of the two, stored MD5 passwords are a bigger surface for attack than user passwords stored in memory for fractions of a second (sys admins are legally bound, and you should be seriously considering other countermeasures if you think a hacker might be able to gain access to your system memory. See: SELinux).

The number of ways to break TLS connections is growing
-I'm not sure whether to say this statement is redundant or false; an updated system is really only vulnerable to zero-day exploits. While zero-days should be considered during planning, we're actually talking about a general security compromise with digest (even if it includes a shift in the attack vector), so I'm going to say this point is moot in the context of digest as a solution (and in light of what I've shared above).

Are you trying to say that Digest Auth is "unnecessarily increasing complexity/server load"? -Yes. Especially because it actually has security drawbacks (like limiting the hashing algorithm you store passwords with).

Other considerations
-exploitable via a Man-in-the-Middle attack. https://tools.ietf.org/html/rfc2617 (refer to section 4.8) -though rfc2617 also added a number of security options, a number of them are purely optional (you'll want to read through the above link for more detail on which features this affects) -based on your concerns, you should really check out that cnet article and consider implementing soft-tokens in place of passwords. They're more secure, and in the event of a compromise, they're unique and disposable.

Hopefully this is digestible (unintentional pun). I'll try to answer any other questions you have, but I'm not sure I'll have the time/energy for another email this long so you may have to keep it to a couple more straightforward questions.

---
Colin Purcell | IT Administrator

On 2016-04-05 5:59 am, Tobias Mueller wrote:
Hi.

On Mo, 2016-04-04 at 19:07 -0400, Colin Purcell wrote:
digest is widely accepted as laughably weak
Do you have any references for your claim?

I think in light of basic auth, digest auth looks more like fort knox.
So it seems only logical to prefer digest auth over basic auth whenever
possible.  InfCloud claims that it is not compatible, but I haven't
seen any instance of such an incompatibility. The documentation also
lacks pointers to said incompatibilities.

My hypothesis is that such incompatibilities do not exist.  In fact,
I'm using (admittedly an older version of) CalDAVMate successfully with
Firefox and Baikal configured to do digest auth.

For now, it seems to me that digest auth is advised against without any
substantiation.  I would like to understand why basic auth is preferred
over digest auth.


 and 
thus a generally unnecessary layer when the entire session
(including 
the authentication process) is already secured via SSL or TLS.
Fair enough, but that's not the argument that InfCloud brought up. The
argument there seems to be "Lot of browsers have wrong or buggy digest
auth support (especially if used from JavaScript)".

Also, I think it's wrong.  I agree that TLS solves many problems. But
it doesn't solve all problems that digest auth addresses.

TLS is not used for client authentication. Nobody does, unfortunately.
So TLS is only used for preventing someone on the wire to mess with
your packets.

But there are more threats than that.  You may not want your
credentials to leak to a curious sysadmin, anyone stealing the
credentials stored on the server, or a broken client implementation of
your protocol.  And mind you, things tend to be more broken than we
think. The number of ways to break TLS connections is growing.

So even if you think that TLS solves all of your problems, some people
find it valuable to have a second line of defence. But you recommend
against it with no good cause, from what I have understood so far.



I would compare Digest Authentication to requiring a second password
for login
I think this comparison is very flawed.  If only because with digest
auth, you don't leak your credentials in plain text to anyone who is
able to get their hands on your traffic.  So the additional security is
very much unlike a second password.

 you're much better off to increase the 
length of the original password (key length for our purposes) or
explore other avenues of security that don't unnecessarily increase 
complexity/server load (one-time passwords maybe? The world is your 
oyster).
Are you trying to say that Digest Auth is "unnecessarily increasing
complexity/server load"?

I agree with the sentiment of your example: It's about making the cost
of an attack much more expensive than defending against them.

And this is exactly why I don't understand that digest auth is frowned
upon.  From what I can tell it's well supported in both servers and
clients.  It costs a round trip and a few hashes. Sure, that's much
more expensive than basic auth, but the attack is much much more
expensive. Unless you convince me that it's "laughably weak", I
maintain the proposition that digest auth provides more value than
basic auth. And I think it's very easy to see.  Even when using TLS.
Combined with what I consider low cost (modulo the yet to see
incompatibilities which would weigh a lot), I don't see how you could
possibly conclude to advise against digest auth.



If you're genuinely interested in the topic, I'd be happy to
elaborate on anything unclear.
Looking forward to reading.

Cheers,
  Tobi

Follow-Ups:
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerTobias Mueller <muelli@xxxxxxxxxxxxxx>
References:
[Inf-IT DAVcl] Fwd: Blank page,with Internet ExplorerAdmin - Muskoka Auto Parts Limited <admin@xxxxxxxxxxxxxxx>
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerJán Máté <jan.mate@xxxxxxxxxx>
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerTobias Mueller <muelli@xxxxxxxxxxxxxx>
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerJán Máté <jan.mate@xxxxxxxxxx>
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerTobias Mueller <muelli@xxxxxxxxxxxxxx>
Re: [Inf-IT DAVcl] Blank page,with Internet ExplorerColin Purcell <colin@xxxxxxxxxxxxxxxxxx>