26 Oct
2008
26 Oct
'08
5:03 p.m.
Hi Sergiu,
On Sun, Oct 26, 2008 at 8:20 AM, Sergiu Dumitriu <sergiu(a)xwiki.com> wrote:
Asiri Rathnayake wrote:
Well, [RFC2518 <http://www.ietf.org/rfc/rfc2518.txt>] clearly states that
all webdav servers 'MUST' support the digest authentication mechanism
(Section 17.1) :
*"Furthermore, a WebDAV server MUST NOT send Basic
authentication credentials in a WWW-Authenticate header unless the
connection is secure. Examples of secure connections include a
Transport Layer Security (TLS) connection employing a strong cipher
suite with mutual authentication of client and server, or a
connection over a network which is physically secure, for example, an
isolated network in a building with restricted access.
WebDAV applications MUST support the Digest authentication scheme
[RFC2069]. Since Digest authentication verifies that both parties to
a communication know a shared secret, a password, without having to
send that secret in the clear, Digest authentication avoids the
security problems inherent in Basic authentication while providing a
level of authentication which is useful in a wide range of scenarios."
*
Also, windows XP by default uses digest authentication and users need to
hack into their registries if they need their built-in webdav client to use
Basic Authentication instead.
There is no technical barrier for us to keep using Basic Authentication (con
: users have to do some tweaking). But it's less secure. Having said that,
even MD5 hashes are reportedly not *that* secure :
http://en.wikipedia.org/wiki/MD5
AFAIK either Cookies nor OpenID can be used because they are inherently
meant for browsers. (WebDAV clients are not browsers most of the time).
Thanks.
- Asiri
Hi Devs,
I have hit a wall trying to implement Digest Access Authentication for
the
xwiki-webdav module. I'll try to be clear as
much as possible.
*+ INTRO* : Digest Access Authentication is used to avoid the
transmission
of clear text passwords over http for
authenticating users. Instead of
the
clear text password, following hash (RESPONSE)
will be transferred to the
server by client,
HA1 = MD5(username,password,realm)
HA2 = MD5(method,digestURI)
RESPONSE = MD5(HA1,nonce,HA2)
Here the 'nonce' is some weird string token generated by the server for
that
particular client for a particular session. So
the RESPONSE instead of
the
clear text password will be transferred to the
server. For more specific
information about Digest Authentication, you may refer [1].
*+ PROBLEM* : Simply put, the way xwiki handles authentication requires
the
presentation of a clear text password by the
client (which is not
available
with Digest Authentication scheme). What we have
with xwiki (on the
server
side) is a crypted version of the original
password.
One possible solution to overcome this limitation is to store the HA1
value
in our databases (is this possible ?). This is
one of the limitations of
Digest Authentication scheme as mentioned in [1] :
*"There is an important problem with implementing Digest access
authentication. This is the requirement that either cleartext passwords
or
the HA1 hashes must be known in order to perform
client response
validation"
*
I would like to know what other developers have to say about this issue,
and
possible workarounds ... [?]
Thanks.
- Asiri
[1] http://en.wikipedia.org/wiki/Digest_access_authentication
Hi devs,
This is a serious roadblock, and it cannot be easily solved.
The main idea is that whatever data we keep in the database of the wiki,
it is accessible. Storing HA1 is as safe as storing a plaintext
password. Anybody with edit access and a bit of cracking/hacking
experience can get it out of the wiki. So I'm a strong -1 against
storing any unencrypted login information.
I can't see any simple and clean mechanism to work around this problem.
There's no way we can validate the correct password. Some hacks we could
use in the worst case are:
1. Something like Niels suggested, authenticate in a third service over
SSL and use a generated token as the password. This is cumbersome for
many reasons, like: this token should expire often, for security
reasons; the need for a certificate + HTTPS configuration; adding a new
service; increased complexity; and many others.
2. Something similar to what is done for the current password. I don't
go into further details now since I'm sleepy, and it's too ugly to be
taken into account seriously.
3. Use Basic auth, but force https to be used. This means that we must
document (or link to external documentation) how to setup https on
various containers.
4. Find the time to implement crypt password storing mechanism. This
means that the password can also be decrypted, unlike the current hash
mechanism. This involves more effort, and is less secure than what we
have now (I'd like that the user's password can never be retrieved, not
even by the wiki and server owner).
5. Try to find other ways to authenticate.
I always try to approach the problem from a different angle, since many
times a difficult technical question is actually the dead end of a wrong
solution to a different problem. So, why do you need to implement Digest
authentication? What is your scenario? What is the goal? Do you have a
link to the WebDAV authentication specification? Can we use cookies
instead? Can we use OpenID authentication?
--
Sergiu Dumitriu
http://purl.org/net/sergiu/
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